Vegetation

Control on

Railway

Tracks and

Grounds

BUNDESAMT FÜR VERKEHROFFICE FÉDÉRAL DES TRANSPORTSUFFICIO FEDERALE DEI TRASPORTIFEDERAL OFFICE OF TRANSPORT

Swiss Agency forthe Environment,Forests and Land-scape (SAEFL)

1

Strategy, Solutions and Limitations 3

Things We Should Know About Plants... 4

Requirements of the Different Track Areas 6

Weighing of Interests 8

Environmentally Favourable Vegetation Control 10

Prevention of Undesired Vegetation 11

Constructional Measures 12

Biological Measures 14

Mechanical Measures 16

Chemical Measures 18

Thermal Measures 20

Selection Criteria 21

Comparison of Different Measures 22

Common Weeds in the Track Area 24

Possibilities and Limits of Vegetation Control 26

Annex: Bibliography, Glossary 30-32

Basic and further education possibilities, Information 33

ContentsImprint

PublisherSwiss Federal Railways (SBB/CFF/FFS),Swiss Agency for the Environment,Forests and Landscape (SAEFL),Federal Transport Office (BAV)

This brochure is based on the reportentitled «Ausgewählte Verfahren zurVegetationskotrolle auf Bahnanlagen» ,by Christian Müller, Swiss Agency for the Environment, Forests and Landscape,1999, in No. 108 of its publication«Umwelt-Materialien» .

Editorial teamChristian Müller, Grossaffoltern;Helmut Kuppelwieser, SBB;Roland von Arx, SAEFL;Rolf Beyeler, Olten

Associated Working Party Federal Transport Office (BAV),Swiss Federal Railways (SBB),Public Transport Union (VöV),Swiss Federal Research Station for Fruit-Growing, Viticulture and Horticulture,Wädenswil (FAW),Swiss Agency for the Environment, Forestsand Landscape (SAEFL)Swiss Federal Roads Office (FEDRO),Swiss Federal Office for Public Health(SFOPH)

Design and layoutTextext Olten

Translated from German by Hans Bamert

PhotographsChristian Müller, SBB DocumentationService, Helmut Kuppelwieser,Jean-Pierre Mettraux, Barbara Bott

Source of supplySBB AG, BernRail Environmental CenterParkterrasse 14CH-3000 Bern 65, SwitzerlandTel +41 512 20 58 19Fax +41 512 20 44 75E-Mail umwelt@sbb.ch

German and French versions of thisdocument are available from the sameaddress.

© BAV/SAEFL/SBB 2001

4.2001 800 52446

2 3

Just how free of weeds the trackarea must be will depend above

all on the operationalrequirements the line must meet.The control measures described in

this brochure are designed toguarantee productive efficiency

and operating safety of therailway in the long term, whilst

ensuring the best possibleprotection for the environment.

Overgrowing vegetation in thetrack area can be a danger to

railway operation. Weeds must becontrolled with measures

appropriate to the location, and to the type and

extent of line use.

Strategy,

Solutions and

Limitations

Modern train operation makes very highdemands on railway tracks. Thesedemands can only be met if the ballastbed is as much as possible free ofvegetation. In earlier years, soil herbicideswere used to achieve this goal. However,the chemicals used (such as Atrazine) hada low degradability. This and the highpermeability of the track sub-structure ledto pollution of ground- and drinkingwater. A working party comprisingrepresentatives from SBB, privaterailways, agricultural research centres, theFederal Transport Office (BAV), the SwissFederal Office for Public Health (SFOPH)and the Swiss Agency for theEnvironment, Forests and Landscape(SAEFL) was set up to take a new look atvegetation control on railway tracks andgrounds.

The working party, chaired by SBB,investigated other methods of vegetationcontrol in an effort to find alternatives tochemicals. Particular attention was givento constructional, biological, mechanicaland thermal measures.

Target Group

To optimise vegetation control from aneconomical and ecological point of view,it is essential for all the technicaldepartments of a railway company to beaware of the problems associated withrailway vegetation and to have somebasic knowledge of the subject. If, forexample, the question of vegetationcontrol is already taken into accountduring the planning and projecting phaseof a new line construction or renewalscheme, this will help to reduce the timeand money spent later by the mainte-nance services. This brochure is thereforedirected to all those responsible for

➠ planning

➠ project work

➠ execution

➠ maintenance

➠ renewal

➠ regeneration

associated with railway installations, or tothose involved in the related activities.

The main concern today is to bringvegetation under control through theuse of a combination of differentmeasures appropriate to the specificsituation. More specifically, thismeans that preventive measuresshould already be addressed in theplanning and projecting phase, andthat the periodical maintenance ofthe lines must be guaranteed. Tocomplement this, existing vegetationis removed using measures thatcombat the symptoms.

This brochure is designed as a basic guidefor anyone involved in vegetation controlon railway tracks and grounds. Itspurpose is to make people aware of thepossible options and problems whilst alsodescribing the current methods and howthey can be combined.

4 5

Things We

Should Know

About Plants...

A basic knowledge of plant growth isa prerequisite for effective vegeta-tion control. This can lead to a betterunderstanding of the interactionsbetween the measures taken andplant behaviour. It can also helpavoid inappropriate applications thatare not effective, or whose effect iseven counter-productive. Reference isalso made in this connection to theoverview of common problem plantson pages 24 and 25.

To grow, plants need light, nutrients, andabove all, water. The less water there isavailable to a plant, the less it grows.

To survive periods of little precipitation,plants depend on the water-holdingcapacity of the soil, which on its part is afunction of the soil structure. Humus, fine-grained silt and clay can hold largequantities of water, whilst coarse-grainedmaterials like washed sand, stonechippings, ballast and boulders do nothave this ability. They repress plantgrowth. A thin separating layer of coarse-grained material is usually sufficient tocut off the roots from the water supply.

Humus also contains many nutrients thatplants also need in order to grow.

The installation of coarse-grainedseparating layers without humus, siltand clay has an extremely stuntingeffect on the settlement and growthof most types of plants.

In principle, three main groups of plantspecies are of importance in track-bedmaintenance. These are described in moredetail below.

Plants are excellent indicators ofthe state of the soil. The rich

growth of horsetail in the pictureshows that the ground in this

area is damp and thereforeunstable. Here, the result has

been track subsidence.

Basic principles of plant growth

Seed dispersionspecies

Most plants propagate and spreadthrough seed dispersion. These types canefficiently be controlled throughconstructional measures designed toinhibit growth.

Seeds normally germinate at the surfaceof the soil and their roots then growdown in search of water. If the roots canlocate neither water nor nutrients – inother words if the ballast bed and vergeare free of dirt able to store water andnutrients – the young plants will simplydie.

For this reason, new verges should bebuilt up with a coarse-grained layer(e.g. gravel, ballast), and in the idealcase should be covered with fine-grained materials such as stonechippings, and should be periodicallymaintained (cf. SBB Regulations211.1). For older verges, a periodicalmaintenance is recommended.

Species propagatingabove ground

Problem plants like brambles or traveller’sjoy propagate by sending out runnersabove the surface. Where a runner comesinto contact with the soil, new rootsform, from which runners are again sentout. If however the runners arecontinually cut back, the plants areunable to propagate further.

Plants that propagate in the trackarea by sending out runners aboveground can be kept under control byregular cutting back and mowing inthe bank area (see «Mowing» p. 15).

Species propagatingfrom below ground

Plants that penetrate the track areaunderground, such as horsetail or reeds,are the hardest to control. These speciesstart by pushing their roots horizontallyout into the damp natural subsoil beforeforming new shoots at the surface, whichthen grow into new plants that send outtheir own suckers. Their roots or shootscan even penetrate heaps of dry gravel,drainage concrete or scree material.

In this way, a whole network of rootsdevelops. This root system can bebetween 1 and 2 metres below thesurface, with extensive, interlinkedramifications spread over a considerablearea, helping the plants to obtain waterand nutrients, even in dry periods. Thesespecies are most common in damp, clayor silty soils.

In the long term, plants propagatingfrom below ground can only becontrolled through renewal of thesubstructure.

A typical seed-dispersion plant iscranesbill.

Bramble is a typical plant thatpropagates above ground.

Reed – a typical problem plant,propagating from below ground.

Zone of intensive maintenance Zone of extensive maintenance

Track area Transistion band Bank

Maintenance goals ✓ ballast bed stability ✓ stability of bank and vegetation✓ durability of materials and verge ✓ protection from projecting

✓ unhindered access or falling wood✓ unobstructed view ✓ protection from the forces of nature

✓ unobstructed view✓ vegetation barrier ✓ vegetation barrier

Vegetation ✓ none ✓ thick grass ✓ various vegetation types✓ no shrubs or trees

Measures prevention and promotion and care ofremoval of vegetation: non propagating plants:

✓ constructional measures ✓ biological measures ✓ Keeping the clearance gauge free✓ chemical measures ✓ Maintenace based on ecological principles ✓ thermal measures including aesthetic considerations

✓ mechanical measures

Factors to consider ✓ Prevention of water pollution ✓ Preservation of nature and the landscape✓ Cost-effectiveness ✓ Cost-effectiveness

6 7

Requirements

of the

Different

Track Areas

Before combating plant growth inand around the track area, two basicquestions must be answered:

➠ Where should or must the track befree of vegetation?

➠ Where is a certain amount ofvegetation to be tolerated, giventhe age, constructional condition,traffic density and time to nextrenewal of the installations?

To be able to answer these questions,it is necessary to know the impor-tance of the different track areas.

The trackbed construction can be dividedinto the ballast bed, the verge and thebank. Each of these areas has a differentrole to play and therefore has specificrequirements on vegetation control. Thisinformation is set out in detail in theSwiss standard «SN 671 560».

Beside a differentiation according toconstruction elements, to differen-tiate between intensive and exten-sive maintenance zones is also impor-tant. Special attention must be givento the 1 to 2 m wide transition bandbetween verge and bank, situated inthe zone of intensive maintenance.

Within the zone of intensive mainte-nance, safety is the paramount consider-ation. While no growth is permitted in theactual track area (the ballast bed), regularmowing of the area between the vergeand the bank should ensure that a thickband of grass forms there to preventweeds from propagating into the trackarea.

Within the zone of extensive mainte-nance, ecological and economical aspectshave to be considered, besides those ofsafety. This can be achieved by regularmaintenance. In particular, the use ofherbicides is forbidden here.

Maintenance zones

Zone of intensivemaintenance

approx. 5 m (from track centre)

Zone of extensivemaintenance

approx. 10 m

track area

transi-

tion

band

1-2m

bank

abso

lute

lim

it f

or t

rees

and

shr

ubs

appro

x. 45

˚

ballast bed verge

8 9

Ballast bed

With the high speeds and loads ofmodern rail traffic, operating safety dic-tates that the ballast bed be virtuallyclear of plant growth.

➠ A dirty or overgrown ballast bed losesthe resiliency that is essential for highoperating speeds.

➠ Plant roots and dirt store water thatcan freeze and expand in winter. Thisleads to a change in track geometrywhich in the worst case can lead toderailments.

➠ Plants that grow over the rails canreduce adhesion essential to powertransmission and braking.

Verges

The verge can fulfill several functions invegetation control depending on thesituation. It can serve:

➠ as an element in the drainage of thetrack;

➠ as a barrier to stop plant incursionreaching the ballast bed;

➠ as a walkway for inspections andmaintenance work.

Good quality verges are also importantfor work to be performed in the ballastarea.

When used as a walkway, it is sufficientto keep the verge free of plants likebrambles, traveller’s joy and shrubberythat might make people stumble overthem. More vegetation can be toleratedon open lines than in marshalling yardsand stations where walkways are usedevery day.

Banks

Professional maintenance of the railwaybanks protects the track area againstlateral plant incursions.

For reasons of operating safety andvegetation control, no trees or shrubs areallowed to grow in the vicinity of thetrack (about 5 metres from the trackcentre). Potential hazards include fallingtrees, lack of visibility, excess shadow,falling leaves and the added humus thatsuch growth would bring.

In Switzerland this protection is ensuredthrough regular attention to the banks inaccordance with Swiss standard «SN 671560».

Weighing of

InterestsWhen maintaining railway installa-tions or carrying out vegetation con-trol, a number of different aspectsmust be considered. Apart from pur-suing the goals of a long-term safetyguarantee, also functional efficiencyand cost-effectiveness of railwayinstallations, the protection of theenvironment, the preservation of thecountryside, and the prevention ofwater pollution, have at any rate tobe taken into consideration. Theessential obligations to be observedare set down in the environment pro-tection law, the law on the protectionof regional values and traditions, thelandscape preservation law, as wellas the water protection law.

Basically, more vegetation can be toler-ated on sidings or lightly used connectinglines. Neglecting maintenance on lightlyused secondary lines will however lead toa rapid deterioration in their condition,with the result that speed restrictionshave to be imposed. The lines may evenhave to be closed.

The distinction between zones of inten-sive and extensive maintenance gives aclear indication of where the vegetationmust be controlled on railway tracks andgrounds and with what kind of measures.These requirements can be applied byanalogy to those areas that are visible tothe eye – the ballast bed, verge andbank. Depending on the characteristics ofthe landscape and the age of a line, theindividual areas can vary considerably insize and condition. The width of the tran-sition band between intensive and exten-sive maintenance zones (i.e. between theverge and the bank) is particularly vari-able, but should be around 2 metreswherever possible.

Transition band

Regular mowing of the transition bandpromotes a dense grassy vegetation. Thisis a good barrier against problem plantsgrowing into the track area from thebank.

The extent to which ballast mustbe free of vegetation depends

above all on the number of trainsand their speeds.

Verges built according toaccepted standards, and in

combination with a grass-coveredand regularly mown transition

band can be an ideal vegetationbarrier against weed incursions.

Regular mowing of the bankkeeps trees and shrubs at bay andprevents weeds from propagating

into the track area.

10 11

Environmental-

ly Favourable

Vegetation

Control

The methods of vegetation controlcurrently used by SBB can be dividedinto two main groups: procedures forremoving or repressing existing vege-tation, and measures directed to thecauses of plant growth. In practice, itis usually an optimal combination ofa variety of measures that is the mosteffective.

In principle, constructional and biologicalmeasures are the most effective when aline is built or renewed (bituminous weedbarriers, porous concrete barriers, lateralbarriers and green bands with selectedvegetation). These measures preventplant growth by reducing the amount ofwater in the substructure and serving asa barrier against plant incursion.

The methods of vegetationcontrol used by SBB today. In

practice only an optimumcombination of measures will

generally deliver a sustainableand cost-effective result.

In the longer term however, these effectswill decrease, which is why it is soimportant to maintain the lines (mowingof the bank in the track vicinity, cleaningout of drains). Even though vegetationcontrol is not the primary objective ofsome maintenance works such as ballastcleaning, these often have a salutary andwished-for side effect.

Where vegetation persists in the trackarea in spite of constructional measuresand regular maintenance, plants can beremoved mechanically, chemically orthermally, depending on what ispermitted.

Prevention of

Undesired

Vegetation

Plant incursion into the track areacan best be prevented or discouragedby ensuring that conditions of growthin the verge are as unfavourable aspossible (reducing the amount ofwater, nutrients and light). However,the success of a given method willdepend on the type of vegetationand the site in question. To combatsome so-called problem plants (see p. 24 and p. 25), other methods thanthose used for normal weeds arerequired.

‘Problem plants’present

The best way to deprive problem plants(e.g. those that propagate from under-ground) of water they need for survival, isto build deep-set drainage systems, andat the same time to replace the wholelayer of soil interspersed with roots. Butmostly, this procedure is possible only inconnection with a renovation of thesubstructure, and it is the most cost-effective if the verge is to be renovatedfor operational reasons.

A cheaper method is to insert foils intothe verge. These foils should be resistantto root growth, degradation and weatherinfluences (see page 13). A preconditionfor this is that water run-off is providedand that sufficiently strong competitionvegetation is stimulated in the adjoiningtransition band. This helps to limit lateralincursions by problem plants (compare«Mowing», p. 15).

‘Problem plants’absent

Seed plants, and plants propagatingabove ground can best be combated byplant- inhibiting construction measures(substructure materials without clay, siltor humus). A sufficiently thick (confor-ming to SBB Regulation R 211.1) andclean ballast bed will be especially effec-tive in durably depriving seed plants oftheir necessary basis of existence. Afterrainfall or other forms of precipitation, itis important for the ballast to dry out asfast as possible – the track should there-fore not be overshadowed by trees. Thelateral drainage of the substructure andthe ballast bed also has to beguaranteed.

Plants usually start to grow at the base ofthe ballast shoulder, where the ballastlayer is the thinnest. Ensuring that a suffi-ciently thick layer of ballast reaches as faras the verge can therefore also helpprevent plant growth.

Well placed and solid cable trenches,concrete border elements, covered porousconcrete barriers and solidly-built vergesare suitable as lateral barriers againstplant incursion into the track area.

As experience shows, a substructuremade of sand and gravel without a bitu-minous layer does not meet the require-ments of a plant-inhibiting constructiondesign. The sand and gravel mix alonecannot ensure complete dryness.

The absence of shade trees tendsto discourage plant growth in the

track area.

Sustainable, environmentallyfavourable vegetation control onrailway tracks and grounds ispossible if the following prioritiesare observed:➠ prevention of plant growth

through appropriate con-structional and biologicalmeasures;

➠ preservation of the growth-inhibiting state throughregular maintenance;

➠ removal of vegetation bymechanical, chemical andthermal means as and whennecessary.

Preventionof undesired vegetation(combating the causes)

Removal and repressionof undesired vegetation

(combating the symptoms)

constructionally

see page 12

biologically

see page 14

mechanically

see page 16

chemically

see page 18

thermally

see page 20

Combination of methods tailored to the situation in hand

Environmentally favourable vegetation control

12 13

Lateral barriers

Verges that are built with a plant inhibi-ting construction, already constitute ef-fective barriers against plant incursion.With the addition of cable trenches, barsand step blocks as lateral barriers, theoverall effect is even enhanced. Whereverges are lacking or need to be raised,concrete slabs in upright position are alsosuitable. However, a proper drainage ofthe track structure must always beensured.

Cost: 300 - 800 sfr./metre

Verge design

Verges with a compacted, wear-resistanttop layer of a finer material will inhibitmost forms of plant growth. A smoothverge surface that slopes towards theoutside has the additional advantage thatalmost no organic matter can settle on it.With time, though, some unpretentiousplants will grow here. To keep the vergefree of vegetation for a longer time,extremely growth-inhibiting materials canbe used for the verge (gravel made ofcalcium-free silicate). Bear in mind thatthis measure on its own will not deterplants that propagate from beneath thesurface.

If the verge and transition band are givenregular care, verges built in this way inareas that are largely free of problemplants (e.g. reed and horsetail) should lastfor anything up to 30 years (except forvery steep banks without shoulders andnarrow cuttings).

Providing the underlying drainage layerand barrier have a proper effect, areplacement of the overgrown, humus-rich layer of gravel on existing verges,provides for a new growth-inhibitingeffect for several years against wild seedplants. The new surface material, selectedfor its grain size properties, willnonetheless need to be compacted.

Verges built on new lines are nowcomposed of ballast because of its betterpermeability. Since in this case vegetationcan only be removed at substantial cost,the verge must be kept free of plantgrowth by regular and professional maintenance (see «Biological Measures»,p. 14).

Cost: 20 - 30 sfr./metre

Insertion of foils

Integrating foils in the construction of theverge is a simple way of preventing plantincursion. These foils must however beundegradable, resistant to atmosphericcorrosion, and must resist root growth ofhorsetail and reeds (e.g. fleece is notsuitable, as plants can grow through it).If, however, problem plants are alreadypresent, then also the foils will not beable to stop them.When the foils are built in, attentionshould be paid to ensuring that waterrun-off from the sides of the ballast bedis guaranteed and that the foil reachesaround 50 cm under the ballast. It mustslope sufficiently outwards, which meansthat the verge surface must previously berenovated. The foil must also be securedagainst the wind using gravel or a similarmaterial.The costs indicated below result from atrial scheme and are therefore ratherhigh. Were the foils to be laid concur-rently with rebuilding work, substantialsavings would result.

Cost: 100 to 150 sfr./metre

Constructional

Measures

Constructional measures designed toreduce the amount of available waterin the track area have proven to havethe best preventive effect againstweeds. However, because of the highcosts involved in the constructionwork and the disruption of opera-tions, measures of this type are notcost-effective if their sole purpose isvegetation control. It is thereforenecessary always to take due accountof vegetation control aspects whenengineering works are planned foroperational reasons. The basicrequirements for constructionalmeasures are set out in SBB Regu-lation R 211.1.

Bituminous weedbarriers

A sufficiently robust and compact layer ofbitumen beneath the ballast is a solidbarrier against rising soil moisture andalso prevents pollution and softening ofthe substructure due to precipitationsoaking into the ground.

Bituminous weed barriers that conform toSwiss standard «SN 640 431b» stop thepropagation of problem plants frombelow almost entirely.

Cost: 20 - 80 sfr./metre

Porous concretebarriers

The porous concrete barriers that SBB hasbuilt in the verges of existing lines sincethe late 1980s are a good barrier againstplant incursion. They can be built quicklyand easily and at reasonable cost, andare therefore particularly suited when ex-isting lines are reconstructed. Concretebarriers for drainage must however notimpede the mowing of the adjacent bandof grass.

Requirements governing the installationof porous concrete barriers are set out inAnnex 9 to SBB Regulation R 211.1. Cov-ering the concrete barriers with a layer offiner material can help to efficiently filterout humus and nutrients.

Cost: 150 - 300 sfr./metre

Where the foil ends, thevegetation spreads.

Solid cable trenches form goodbarriers to the incursion of plants.

Properly built and maintainedverges can repress undesired

vegetation for up to 30 years.

This gap in a porous concretebarrier illustrates the

effectiveness of this technique.

Bituminous weed barriers todayare standard procedure for SBB,

among other constructionalmeasures.

Greening

The deliberate sowing of desired plantswill generally follow after completion ofthe engineering work and focus on thetransition band in the track vicinity. SBBexperience shows that the transition bandshould ideally be sown with seeds adap-ted to local conditions as soon as possi-ble after completion of the engineeringwork (preferably in the spring). Leavingthese areas for spontaneous plant cov-erage will often result in a large propor-tion of problem species. This can happenespecially where new earth containingseeds and particles of plants able togerminate is spread in the area borderingon the bank. On the other hand, sponta-neous natural plant coverage shouldgenerally be encouraged in the zone ofextensive maintenance. Banks that areliable to erosion and subsidence shouldhowever be planted quickly (see SBBhandbook «Grünflächen bei Bahn-anlagen, Projektierung», chapter D«Begrünung»).

Cost: approx. 5 sfr./square metre

Without regular attention, vegetation willdevelop into woodland in most cases. It istherefore important to mow the grass inthe zone of extensive maintenance atleast once a year. Longer intervals willlead to the growth of wooden plants anda higher proportion of wood in the plantmaterial that the mower encounters. Thelatter results in a higher consumption ofenergy, and a lower performance persurface unit. Problem plants like Japaneseknotgrass, brambles and reeds tend tospread far more quickly if mowingintervals are longer.

Mowing is effective for up to a yearagainst growth of brambles, traveller’sjoy, bushes or trees on a soil favourableto meadow plants. Regarding horsetailand reeds, this effectiveness lasts roughlyhalf as long. For this reason, during thegrowth period at least one to twomowing operations a year will be neededon the transition band.

With a greened verge (see page 28),note that this indication applies onlyif no herbicides are used in the areabeing mowed, as herbicides willdestroy the plants that competenaturally with horsetail and reeds.Horsetail, which is resistant toGlyphosate, will even benefit fromthe operation.

In this connection it is mandatory topay attention to the fact that the useof herbicides with few exceptions isforbidden in the bank area!

Below, an overview is given on the mostcommon mowing methods used by therailways:

ScythePurely manual work, noiseless, but withlow surface area coverage.

14 15

Biological

Measures

Biological measures are used toshape and treat the transition bandand the bank so that only such plantscan grow on them as do not interferewith railway operation and mainte-nance.While constructional measures mostlymean a change of the soil structure,shaping work means the sowing orplanting of non-interfering species,appropriate maintenance, selectiveweeding of the bank, removal ofshrubs and trees and regular mowingor grazing. All of these works requireadequately trained specialists.

Influencing the composition of the plantspecies requires knowledge in the fieldsof:

➠ soil quality;➠ habitat requirements and the ability

of single plant species to competewith others;

➠ plant reactions to specific treatmentmethods.

For example, the different competitiveabilities of plants can skilfully be used togood effect. Since regular mowing isharmful to those plants that send outrunners, these species will be supersededby others less or not at all affected bysuch a measure. To ensure that this oust-ing mechanism functions properly, thelocal conditions (particularly the soil com-position) must be such as to encouragethe growth of the favoured plant species.

Wet, clayish and compacted soils, whichfavour the growth of problem plantspenetrating underground into the ballastbed like horsetail and reeds, should eitherbe replaced to a sufficient depth near thetrack, or drained, or improved. Only inthis way, problem plants can be super-seded. A welcome advantage here is the

fact that at specific places, the replace-ment of unsuitable, loamy soil has alwaysbeen a tried method of the railways toimprove track stability.

Knowledge of the biological interactionsbetween the soil, the competitive strate-gies of plants and their reaction to speci-fic types of treatment is also useful fornew line constructions, where, dependingon the situation, measures to preventerosion are necessary.

Apart from constructional measures thatare unavoidable in problem areas in the long term, biological maintenanceremains a standard activity for railwaycompanies. To perform it optimally, it iswise to work with an official green areacadaster.

With the exception of mowing, thecosts of biological measures cannotbe stated with any accuracy becauseof the big differences between thelocal conditions.

Loose vegetation and notsufficiently frequent mowing

promotes the growth ofunwanted plant species in thetransition band (e.g. thistles).

Motor scytheBest used to mow around obstacles andin areas that are difficult of access or notsuited to larger equipment.

Motor mowerUsed mostly on smaller or sloping areasand to protect valuable plant stands.

Rotary mowerMowing device mounted on a tractor. Thecuttings are usually left on the ground asmulch. It is important that the cuttingsshould not be spread onto the ballast orverge. A newly-developed bank mowercaters to this requirement by blowing thecuttings out into the bank area.

Self-propelled rotary mowerAll-terrain, 4-wheel drive vehicle with afront-mounted mowing device. Possiblesideways slippage can damage the bank.

Rotary mower with suction deviceThis is similar to a standard rotary mower,but fitted with a suction device to collectthe cuttings in a mobile container. Toprevent further enrichment of the humuscontent of ballast and verge, use ofsuction equipment is recommendedabove all in cuttings and on the mountainside of sloping terrain. Usually, onlycuttings from the band of greeneryimmediately adjacent to the ballast areremoved by suction. However, to protectanimal life in the bank, this procedure isnot recommended in the zone ofextensive maintenance.

Cost: 0.2 - 0.7 sfr./square metre

Selectivemaintenance

Outside the area of intensive mainte-nance, a low-maintenance vegetationsuited to local conditions can be achievedby selective thinning out of trees andshrubs in compliance with Swiss standard«SN 671 560». Preference is given hereto slow-growing and small species.

Particularly undesirable plants can beremoved by selective weeding by hand,hoeing or cutting. Especially in shadyplaces such as wooded recesses, seed-lings of trees or bushes are often to befound, which should be removed inautumn and winter.

The production of a green area map orcadaster can be extremely helpful forplanning and implementing specialenvironment-friendly measures such asthese.

Cost: 1 - 3 sfr./square metre

The picture clearly shows thedifferent control methods used

for areas of intensive and ofextensive maintenance.

Mowing

16 17

Mechanical

Measures

Plants are removed from the trackarea by mechanical measures.Therefore these measures belong tothose attacking the symptoms. Withballast cleaning and suction devices,not only the plants themselves areremoved, but also the dirt which isthe basis of their existence. As suchthere is also a preventive dimensionto this kind of work. Although boththese procedures are used first andforemost to guarantee track stability,they fulfill also an essential role invegetation control.

Ballast cleaning

If the ballast bed is to remain free ofweeds in the long term, then ballastcleaning is an important measure. Aballast bed that is clean and dry through-out will not permit plant growth, thoughpropagation of problem plants frombelow ground is still possible.

The ballast cleaning machines used onthe SBB network pick up the dirty ballastwith a conveyor scoop or an excavatorbelt. The material thus extracted is passedthrough a mechanical cleaning system inwhich the fine particles are sifted out. Thecleaned ballast is then spread backbeneath the track.

A good ballast cleaning can be effectivefrom 20 up to 40 years, depending onlocal circumstances and traffic density, ifthe adjacent verges and banks have beenbuilt and planted in compliance with therules, and are properly maintained.

Cost: 300 - 500 sfr./metre

Mechanical weeding

There exist a few machines that can weedand clean the verge, but none of themhas been heavily tested as yet. Bymechanical peeling of plants from thesurface during dry summer weather, it ispossible to defer the constructionalrenewal of the verge by several years. It ishowever important that the materialremoved, which is rich in humus, is notleft lying on the inspection walkway orthe ballast bed. This procedure can onlybe used on gravel verges and surfaces.Daily performance is 1 to 2 km.

Cost: with machine operator, butwithout lookout man

approx. 1 sfr./square metre

There are several manual weedingmethods. For example, the plants can becut off or hoed out level to the groundwith a sharp implement. Either all plantsare torn out, or particularly undesirablespecies only (with the roots if possible).This produces more or less loose hollowsin the verge which can further encourageseed germination. Some weeded areasare therefore treated with Glyphosatewhen the new plant cover has reached aheight of 5 to 10 cm.

A weeding experiment on a limited area(eradication of common cranesbill inballast) showed that the hourly perfor-mance per person was approximately 30square metres. A thick growth of horsetailwas removed from the ballast shoulder,and the performance was about 33square meters. On larger areas however,it will not be possible to achieve this levelof performance.

Suction method

A suction device mounted onto a road-rail vehicle removes unwanted material(cigarette ends, organic waste, leaves,humus, sand, etc.) from the surface of theballast bed. This operation thus contri-butes to the prevention of weeds onrailway tracks. Since the vehicles movevery slowly and therefore occupy the linefor a long time, they are only used in andaround stations and on lines with littletraffic. For operational safety, it is alsovery important that compacted ballastdoes not become loose as a consequenceof this kind of treatment.

Cost: 4 - 5 sfr./metre

A ballast bed that is clean fromtop to bottom, largely prevents

plant growth.

Manual weeding is comparativelycostly, but it allows a selective

approach. Its effect varies quitemuch. Especially in the case of the horsetail, the effect

does not last long.

By removing dirt and rubbishfrom the ballast, a preventive

contribution is made tovegetation control.

Weeding machines for vergeshave not yet been tested on a

large scale. Their use is onlysuitable if combined with other

measures in the track area.

The effect of weeding will depend verymuch on the plant species, the thicknessof the plant cover, the time of year, thelocal growth conditions, the weather andthe seed reservoir in the soil.

Cost: 4 - 5 sfr./metre

Manual weeding

18 19

Chemical

Measures

Use of chemicals to remove individualplants from the track area is a deli-cate matter, considering their impacton nature and the environment. Theoperators must therefore be expertsand act responsibly. For this reason,use of chemicals on SBB is governedby instructions «Chemische Vegeta-tionskontrolle bei den SBB», in whichdetailed, binding rules are set out.One specific requirement limits theworking with herbicides to staff inpossession of a valid authorisation,or acting under the guidance of anauthorised person. Apart from furtherrestrictions, the use of herbicidesoutside the track area (ballast andverge), in the vicinity of rivers andlakes, and in ground water protectionzones S1 and S2, is forbidden.

The restrictions and bans on herbicides,necessary to protect human health andthe environment, are determined everyyear by the Federal Transport Office (BAV)in directives for all railways holding afederal licence (BAV, 2001).

Back-pack spraying

Some 80 – 90% of all spraying on SBB isdone using back-pack sprayers.

With a constant spray pressure of 2 barsand an average walking speed of approx.1 m/s, about 50 litres of fluid will beneeded per hectare.

Because of the fine spray mist, there is aconsiderable risk of the sprayedsubstance being blown away by the wind.Work should therefore be stopped duringstrong winds.

It is essential that the fluid be applied tothe plants only, as otherwise thetreatment will not be effective and cancause damage to adjacent property. Thedirection of the spray nozzle musttherefore constantly be adjusted to thearea being treated – standard practice fordecades in viticulture and horticulture. Itis also important that the spray always bedirected towards the ballast bed from theexterior.

An SBB back-pack spray team will treatan average of 11 track kilometres perday.

Equipment investments (not includingvehicle and training) amount to around2000 sfr. per team.

Cost: 0.2 sfr./metre

Spraying train

Only a few motorised spraying units arestill in use on SBB. These units aremounted on small wagons («Sputniks» )and pushed by a light rail motor tractor.They are designed for an operationalspraying speed of 15 km/h. A dosagedevice (Dosatron) provides a constantmixture of concentrate and spray water,which avoids leftover fluids and meansthat work can be stopped and startedagain at any time. The risk of waterpollution from spillage is very low.

Cost: 0.25 sfr./metre

Leaf herbicides like Glyphosatecannot be used preventively, butare applied directly to plants ofexisting vegetation. The effect ofGlyphosate depends on thegrowth conditions, the presence ofproblem plants with undergroundpropagation, the seed stored inthe soil and the number of seedsbrought in by the wind. This effec-tiveness can last for anythingbetween 10 days and 2 years.

In conditions that are not favou-rable to growth, with treatmentcarried out at the right time andproper tending of the adjacentland, Glyphosate-based weedcontrol can be successful over alonger period. It is recommendedthat the intervals between appli-cations are varied (see SBBinstructions «Chemische Vegeta-tionskontrolle bei den SBB») toensure that the vegetation doesnot have a chance to adapt to thechanged conditions.

Compared to the soil herbicide Atrazinethat was in regular use on the railwaysup to 1989, the leaf herbicides containingthe agents Glyphosate and Sulfosate, thatare permitted today, bind better with theballast and verge material where theydegrade relatively quickly. Unlike with thesoil herbicides, only small quantities ofleaf herbicides are used now. These areabsorbed by the plants through theirgreen parts only and therefore cannot beused preventively.

In principle, the use of herbicides isbanned in the banks alongside the tracks.An exception is the treatment ofindividual problem plants where thesecannot be controlled by other measures,such as regular mowing.

Use of Glyphosate has been optimised forrailway needs, including back-packspraying devices and spraying trains.

An operation that lookscomparatively easy but makes

heavy demands on the expertiseof the staff.

Correct and responsible spraying of leaf herbicides requires in-depth training.

For further information, please refer tothe SBB instructions «ChemischeVegetationskontrolle bei den SBB».Track sections

● ground water protection zonesS1 and S2

● areas with protection statussimilar to ground waterprotection zones S1 and S2 (private drinking water sources,seepage and drainage installations)

● in a buffer zone of 3 m alongsidesurface waters

● bridges

● track to be renewed before theend of June of the current year

Other railway ground

● trackside and roadside banks

● forecourts, parking and storageareas

● platforms

● loading platforms

● roadways and paths

● roofs

● terraces

● directly in and in a buffer zoneof 3 m alongside hedges orsmall woodlands

Areas in which the use of herbicides is prohibited

20 21

Thermal

Measures

Thermal methods of vegetationcontrol such as infra-red (IR), burning,hot steaming and hot water treat-ment destroy plant cells through theeffects of heat. Apart from the highenergy consumption with the atten-dant financial and environmentalconsequences, also the generallyshort effect of these measures makethem highly questionable.

Basically, only those parts of plants thatlie above ground can be damaged bythermal measures. Their effect is thereforemostly short-lived and for plants thatform runners or have strong roots, theimpact is particularly slight, as was clearlyshown in several trials.

Ecological audits have shown that toobtain with thermal measures the samedegree of vegetation absence as withchemical measures, 5 to 14 times moreenergy is consumed (a satisfactory resultfrom thermal measures requires severalapplications). This is also the main reasonwhy this method has hardly been used inSwitzerland to date.

Apart from the methods presented here,there are others which for railway appli-cation are as yet only in a trial stage (e.g.hot steaming).

Burning

Burning of plants with a propane burnersimilar to those used as point heater onSBB is admittedly effective at the begin-ning, but this tends to be short-lived sincewithout a supply of heat to convert theliquid propane into gas, the pressure soonsubsides.

The coverage achieved in an experimentreached 0.6 square metre/minute withpropane consumption of around 222 gper square metre.

Infra-red devices

Combustible gases like propane arecurrently the cheapest source of energyfor producing the type of infra-red thatcan be used to destroy plants. As theheated plates that radiate the infra-redrays need to be placed as close aspossible to the surface, the area must beflat and free of obstacles for the mobileequipment to pass.

The models on the market include deviceswith a constant surface coverage (such asThermflex) and others whose coveragediminishes after a short period of usedepending on the temperature (such asPuzzy Boy).

The costs associated with thermal methods cannot currently be determinedto any degree of accuracy. Once the ongoing SBB test with hot steaming iscompleted, the corresponding figures should become available.

Particularly young plants with asyet only a few leaves can

relatively easily be eliminatedwith thermal methods and

corresponding expense of energy,however the duration of effect isvery short. And the real problem

plants such as horsetail cannot beeliminated in this way.

Selection

Criteria

The overview given on the followingpages shows the benefits and draw-backs of different vegetation controlmeasures in regular use on railwaygrounds today. When deciding on thebest procedures, not only the tech-nical pros and cons should be takeninto consideration, but also thelonger-term consequences in regardto costs and environmental impact.

Although the constructional measureshave clear benefits, they can, for reasonsof cost, normally be applied in tandemwith scheduled renewal work only. This iswhy, in order not to discontinue railwayoperation, recourse must be taken toother measures that tend to attack thesymptoms only. It is precisely with thesemethods that particular attention must bepaid to environmental considerations. Sowhilst grasses and herbs can be success-fully treated with the comparativelycheap herbicide Glyphosate, the samesubstance can under certain circumstan-ces encourage the spread of horsetail.

Environment factor

In vegetation control today, not onlycheap, but also environment-friendlymeasures with a lasting effect are requi-red. This is why priority is given toconstructional and maintenance-relatedmeasures having a preventive effect. Thisdoes not mean, however, that the properuse of permitted leaf herbicides to elimi-nate existing vegetation is fundamentallyless environmentally friendly than non-chemical procedures. Ecological auditshave shown that many measures thatmay appear environmentally-friendly atfirst sight are in fact more damagingbecause of their high energy consump-tion, than the carefully targeted use ofthe leaf herbicide Glyphosate.

Methods attacking the symptoms are byno means a panacea that can meet allthe financial, operational and environ-mental requirements imposed on vege-tation control. Quite the contrary – withthe increasing age of the railway installa-tions, also the number of treatmentsneeded each year to clear the track areaof vegetation increases. This means thatthe most energy is expended on surfaceswith the best growth conditions. The ratiobetween energy use (high environmentalimpact) and benefits obtained, constantlydeteriorates. However, in the interests ofrailway operations, we have no optionbut to resort to these measures. At thesame time, it might be worth consideringwhere a certain amount of growth can betolerated until the next renewaloperation.

Cost factor

From a financial point of view, it is thelong-term cost-effectiveness of thevarious procedures that is of primeinterest. Constructional measures forexample are extremely expensive but alsoeffective and have a long-time effect. Inmost cases, they also have other, positiveside-effects at operational level.

For vegetation control, top priority goesto preventive measures. For this reason,the corresponding requirements need tobe included into the planning and project-ing phases of construction projects.Incorporating vegetation-specific con-cerns in the planning phases can bringsubstantial cost savings, and later savecosts for direct action in vegetationcontrol.

The same goes in many respects for themaintenance work needed for all types ofrailway installations. On a well-main-tained line, the time and money neededto remove unwanted plants will be con-siderably less than on a line whereupkeep is poor.

Before deciding on one measureor another, the situation shouldbe carefully considered and theimpact of the various optionsanalysed. What is supposed to bethe direct path does not alwaysproduce the desired result.

22 23

Comparison of Different Measures

Procedure Benefits

Constructional measures Bituminous weed barriers Optimal for keeping vegetation away from the ballastbed and the verge; stops underground incursions byproblem plants

Verge design Ballast bed lastingly free of vegetation; reducesmower cuttings in the verge; herbicide use can bedrastically reduced

Lateral barriers Ballast bed lastingly free of vegetation; reducesmower cuttings in the verge; herbicide use can bedrastically reduced

Porous concrete barriers Ballast bed lastingly free of vegetation; reducesmower cuttings in the verge; herbicide use can bereduced; cheap!

Insertion of foils Long-lasting barrier to plant growth; reduces mowercuttings in the verge; herbicide use can be drasticallyreduced

Biological measures Greening Suppresses problem plants, prevents rapid spread ofplants with runners; protects against erosion

Mowing Suppresses problem plants, prevents bush growth andrunner incursions; protects against erosion

Selective embankment maintenance Treatment suitable to local conditions; flexibleapplication, not subject to weather conditions

Mechanical measures Ballast cleaning Lasting effect against seed-dispersion weeds

Suction method Slows the formation of humus; specially effectiveagainst seed-dispersion weeds

Mechanical weeding Longer absence of vegetation in the ballast; reducesmower cuttings on the verge; use of herbicidedrastically reduced

Manual weeding Flexible application, not dependent on weatherconditions, energy-saving, low environmental impact

Chemical measures Back-pack spraying Cheap, line possession not necessary, energy saving,targeted application

Spraying train High surface area coverage

Thermal measures Burning Easy to implement

Infrared devices Small, lightweight equipment

Line must be closed during installation Best installed during construction or completerenewal

Protects substructure and the natural subsoilfrom water penetration, giving longer life as aresult; cost-effective construction method

Line possession or hindrance Everywhere between the ballast bed and thebank

Protects substructure and the natural subsoilfrom water penetration, giving longer life as aresult; cost-effective construction method

Line possession or hindrance Everywhere between the ballast bed and thebank

Easier access to inspection walkways; lateraldrainage of the ballast bed, depending onlocation and structure

Line possession or hindrance; possibleclogging of drainage systems as lime iswashed away

During the renovation of existing railway lines;dams where space is confined

Drainage, leading also to better trackbedstability, stable bank shoulders with littleavailable space; inspection walkway

Line possession or hindrance; can hinderlateral drainage

In the verge (especially at the renewal of existinglines and in ground water protection zones)

Easier access to inspection walkways

Line possession required where access fromoutside not possible

In meadowland and poorly-stocked areas; in thetransition band and adjacent bank

Protection of nature and countryside; well-tended bank (image); protection againsterosion

Line possession required; cost-intensive Necessary throughout to ensure longevity fortracks

Gives an opportunity to make minoradjustments of the track level; elasticpositioning of rail surface

Requires knowledge of existing vegetation Wherever necessary, in the extensivemaintenance area, in areas with bushes andhedges

Protection of nature and countryside (protec-tion of rare plant species possible); stabilisesthe bank and improves operating safety

Line possession required where access fromoutside not possible

After construction work, when plant cover in thetransition band is patchy or absent; in bank areasprone to erosion and slippage

Protection of nature and countryside; well-maintained bank (image); protection againsterosion

Line possession necessary; no depth action;cost-intensive

Removal of surface material (humus, cigaretteends, rubbish, leaves, etc.) especially in stationareas and on lines through forests

Removal of dirt in station areas (image)

Line possession necessary, cannot be appliedeverywhere; cost-intensive

In the presence of humus on compacted gravelverges (cuttings, slopes, ground water protectionzones)

Easier to walk on inspection walkway

cost-intensive; often short-lived effect only Selective removal of individual plants, clearing ofsmall areas (e.g. in ground water protectionzones)

Easier to walk on inspection walkway; removalof plants reduces humus formation

Line possession necessary, cost-intensive;dependent on weather conditions

Big trackyards with little traffic (e.g. shuntingyards)

None

Requires specialist knowledge; effect dependson location and weather; encourages growthof resistant horsetail

On ballast shoulder and verges; no preventiveeffect

None

Poor propane consumption to effect ratio;destruction of plastic components; danger offire; air pollution

Application not recommended None

Limited impact on luxuriant growth; danger offire; risk for plastic components; air pollution

For minor growth (seedlings) on easily-accessible,level surfaces free of obstacles

None

Drawbacks Optimum range of use Synergy effects

24 25

Common

Weeds in the

Track AreaMost of the plants to be found in thetrack area propagate by seed disper-sion. Many are perennials and diffi-cult to control from the second yearonward (e.g. creeping thistle). For thisreason alone, measures that preventplant growth (by taking away theirsupplies of water and nutrients, or bysetting up competition with other,comparatively harmless species)should be given particular considera-tion. Furthermore, many problemplants grow on soil structures thatare also bad for railway operation,and in areas where soil replacementwould be recommended anyway. Thefollowing overview looks at five typi-cal problem plants commonly foundin the track area and outlines thebest way to deal with them.

Horsetail Cranesbill, Herb Robert

Japanese Knotgrass

Reeds Brambles

Equisetum arvensePerennial, with much-branched, extensiveroot system reaching down to a depth of1 or 2 metres. Propagates through rhizo-mes and sprouts. Penetrates the trackarea from below. Sandy or gravelly cover-ings and old ballast dumps encourage itsgrowth.

Control: Complete removal can only beachieved by constructional remediation ofballast and verge. If this is not possibleand the growth is problematic, horsetailgrowing in the ballast can be torn out byhand. This is expensive and must be re-peated several times a year, as the rootsgenerally remain in the ground and theplant regrows quickly.

Treatment with Glyphosate should beavoided by all means! It has no effecton horsetail and even encourages itsgrowth by eliminating competing plantspecies. A thick growth of grass adjacentto the verge to compete with the horse-tail will stop its spreading quite effectiv-ely.

Deep-seated drains and compactasphalt layers are the most effectivemeasures against horsetail.

Geranium sp.Annual or biennial, with a thin taproot,grows to a hight of 10 to 50 cm; hasreddish flowers and produces seeds fromApril to October; propagation with largenumbers of seeds. Spreads rapidly especi-ally in the ballast of shunting and mar-shalling yards. Hardy, germinates in latesummer where damp persists in fine-grained matter and impurities of ballast.It spends the winter there as a hardlyperceptible seedling that grows up fast inthe spring. Growth of cranesbill willincrease the humus content of the ballast.

Control: Glyphosate treatment, afterlocal inspection, must take place withoutfail before plant reaches seeding maturityin the spring (approx. late April). At thisperiod, only areas where cranesbill pre-dominates should be sprayed, as Glypho-sate has as yet no effect on some otherplants. In cases of thick growth, a secondtreatment is recommended before thenext generation goes to seed.

Treatment after seeding maturity willactually encourage the spread ofcranesbill!

Reynoutria japonicaPerennial, thin-walled stems up to morethan 3 metres tall and 4 cm across, vulner-able to frost. The rapid growth stops endof May. The root system, serves to storenutrients and from its buds, stems growabove the ground. It spreads out belowthe surrounding vegetation at a rate of upto 2 metres per year. Reproduction takesplace mainly via the rhizomes, and also(though rarely) via the stems. In poorlymaintained banks and also on gravel andold ballast areas, it will supersede thesmaller, established vegetation and growinto the track area from below.

Control: Must be cut back to nearground level in early August. In Septem-ber, when the stems are around 40 cmhigh, they are treated with Glyphosate,and the following year, when the newgrowth has reached about the sameheight, mow it or treat it again withGlyphosate. Further propagation can beprevented by regular mowing (five to sixtimes a year) and adjusting the soil condi-tions (possibly in combination with lateralbarriers).

To achieve sustainable elimination,specialist advice must be sought.

Phragmites sp.Grows up to 4 metres in height;perennial, with long underground suckersover a metre deep. Spreads throughrhizomes and suckers, to a lesser extentby seeds. In soils with a poor load-bear-ing quality, damp and generally rich innutrients, reeds will penetrate into thetrack area below ground from untendedbanks.

Control: Annual mowing of greenedverges and adjacent transition bands inJune/July (and again in mid-September ifnecessary). Subsequent growth in theverge should be treated with Glyphosatewhen knee-high from the end of August.Good drainage of the track area (possiblyin combination with lateral barriers).

Mowing is necessary in June/July, asby this time, the larger part of thewinter reserves has been taken upfrom the roots and is not availablefor lateral propagation.

Rubus sp.Perennial; runners up to 7 metres longgrow out from the rootstock. From earlyAugust, their ends grow back into theground and form new rootstocks. Propa-gation by runners growing into the soil,root pieces, also to some extent by seeds.Incursion into the track area by spreadingfrom unmaintained banks above thesurface.

Control: Annual mowing of greenedverges and adjacent transition bands, inJune/July (optimal time), and again if nec-essary in mid-September. Subsequentgrowth in the verge can be treated withGlyphosate from late August.

Mowing in June/July is necessary, asby this time, the larger part of thewinter reserves has been taken upfrom the roots and the subsequentgrowth is much less strong. Glypho-sate treatment alone will seldom befully effective.

26 27

Possibilities

and Limits of

Vegetation

Control

How long any of these measures willbe effective depends very much ongrowth conditions and local climate.In some cases, the effect can be veryshort, and it is here that the watersupply to the soil, and the weather,play a central role.

Without first making a site evaluation, itis virtually impossible to predict how longthe measures of attacking the symptomswill last. At most, a certain timeframe canbe estimated. Constructional measures torepress plant growth, adapted to localconditions, can prolong the effect of othermethods.

In most cases, the best solution is acombination of various measures, as theuse of a single method generally has aselective effect: one species is beingrepressed, while another is encouraged.

The best approach is generally acombination of methods, toensure that gaps left in the

vegetation are not taken up byother unwanted plant species.

The example in the picture showsthat a one-sided treatment withherbicides extremely favours the

propagation of horsetail!

Most vegetation control measures have amore or less selective effect. In otherwords, whilst a given method kills a givenplant, other species have more room tospread. Armed with this knowledge, wehave the possibility to take carefullytargeted action to favour individualspecies and repress others.

Regular tending will always lead to ashift of the composition of the floratowards species that are not much or notat all harmed by the measures taken. Byregular mowing, for instance, we promotegrasses, while species that form runners,bushes and trees, are repressed. If we usethermal methods to combat vulnerableannual or perennial plants with noparticular storage capacities, we therebyencourage plants with undergroundreproductive systems (dandelion) orproblem plants with underground suckerssuch as horsetail.

If Glyphosate is used only once a year,new plants can grow on the treated areain the meantime, given favourableconditions. This new vegetation willcompete with and/or hinder the growthof horsetail, which is resistant toGlyphosate. If Glyphosate is used severaltimes per year, on the other hand, thegrowth of this seasonal rival vegetation isrepressed and the way is clear forincursions by horsetail. To createcompetition for undesired weeds, aregularly mowed and maintained plantcover should be tolerated on older ordirtier verges.

Selective impact

Plants that are relatively harmlessin railway operating terms can

provide competition in thetransition band against lateral

weed incursions.

This last example shows clearlythat caution and circumspectionare required in the choice ofcontrol measures, if we do notwant to effect the opposite ofwhat we originally intended.

Long lastingvegetation control

In vegetation control, constructional growth-inhibiting measures are especiallyeffective. In the longer term however, ourclimate will always tend to create newhabitats for plant growth as a result oferosion, frost, accumulation of dust, plantmaterial, seeds and nutrients, and in theballast bed additionally with fine attritionparticles.

Aside from problem plants growing intothe area below ground, the soil, after aphase without plant growth, is firstsettled by unpretentious plants. These willconsume the little amount of water avail-able in the soil, so that at first, no othervegetation will be able to compete. Withongoing formation of humus, other moredemanding species will establish them-selves, provided there is sufficient supplyof water and nutrients.

Today, there is no cost-effective andenvironmentally-friendly method ofensuring that an area remains free ofvegetation in the long term, if conditionsare favourable to plant growth. Properlyexecuted constructional measures torepress plant growth, and adequatemaintenance, however will prolong theperiod during which plant cover is at anacceptable level by several years.

Combined measures

Given that every measure has a more orless selective effect, the gaps that are leftwill soon be populated by other planttypes if the growth conditions are right.The situation is different if severalmeasures are combined. For instance,mechanically scraping away of a surfacelayer of humus in the verge will createfavourable conditions for Glyphosatetreatment in subsequent years, becausenewly germinating plants are deprived ofnutrients. An even more lasting impactcould of course be achieved by recon-structing a good verge, fitting an effectivedrainage system or even installing acovered porous concrete bar.

Glyphosate treatment of seed dispersingweeds in the verge is an ideal comple-ment to mowing in the adjacent land tocombat lateral incursions of plants suchas brambles, traveller’s joy and reeds. Thetwo measures must however be properlystaggered or co-ordinated to ensure theireffect is properly felt.

It is precisely when combining differentmeasures that a green areas map orcadaster will prove particularly useful.

28 29

The image of therailway

Last but by no means least, it is worthconsidering the railways’ image in theeyes of their customers. The attentiongiven to the maintenance of the banks,respectively the state of the banks itselfand their appearance, are things thatpassengers notice. This in turn influencestheir opinion of the railway - an opinionthat should matter to us!

Benefitting fromsynergy effects

Vegetation control measures, if properlyapplied, can generate synergiesbenefitting other railway activities.

Porous concrete barriers, for instance,bring a whole string of advantages forrailway operations:

➠ greater firmness for the subgrade;

➠ more durable construction;

➠ greater stability for embankmentshoulders;

➠ improved safety for staff (goodinspection walkways);

➠ ballast shoulder stays free ofvegetation for a longer time;

➠ less mower cuttings on the verge;

➠ effective barrier against plants (ifproperly maintained);

➠ low maintenance costs;

➠ low use of herbicides.

Monitoring resultsis important

Monitoring of results is of centralimportance and requires a wholisticconsideration of local conditions by aspecialist – someone who can examinethe vegetation present in the individualparts of the track, and draw conclusionsas to the maintenance carried out so far,and the local properties of the soil.

Well-maintained banks can have a positive influence

on passengers’ opinions on the railway.

A plant cover maintained in such a wayconsumes and evaporates also vastquantities of water and protects the soilfrom erosion at the same time. The fineroots also act as a filter preventing veryfine particles of soil from entering thedrainage system. What is vital, however,is that the verge really is maintainedregularly and that the cuttings are notleft to lie on the verge, so that no plantscan grow into the ballast.

Older, naturally greened andwell-maintained verges can make

an excellent contribution tovegetation control, thanks to

their manifold functions.

Wherever plants can grow, and have beenremoved, new ones will soon replacethem. However we have the possibility tochange the frame conditions for them(e.g. the soil properties). As not all plantsfavour the same conditions, we can thusexert an influence on the range of speciesgrowing in an area. This is a way ofensuring that eventually, we will onlyhave species that do not pose problemsfor railway operation and maintenance.

The extent of annual growth is dependenton local conditions, and on the watersupply first and foremost. As long as thetrackbed is clean from top to bottom,there is no risk of vegetation taking holdin the ballast. If there is proper lateraldrainage of the ballast bed, then until thenext remediation of the verge, it willsuffice to simply maintain the green verge(regular mowing to prevent the spread ofrunner-forming weeds, or resistant seedplants).

Green verges

The example of porous concretebarriers shows how vegetationcontrol measures - above allthose related to construction andmaintenance - can also have apositive effect on operations.Conversely, measures designed tolimit plant growth can often beeasily and cheaply incorporatedinto construction projects thathave their own operationalnecessity.

30 31

Bibliography

SBB Instructions

● Chemische Vegetationskontrolle beiden SBB (W Bau GD 24/96), Bau GD,Bern 1996

● Unterhalt der Grünflächen: Gräser undGebüsche (W BT 38/97), Bau GD, Bern1997

● Bepflanzungsraum (Wuchsraum) (W BT 13/89), Bau GD, Bern 1989

BAV Instructions

● Weisung betreffend chemischeVegetationskontrolle im Gleisbereichder Eisenbahnen in den Jahren 2001-2005, BAV, Bern 2001

SBB Regulations

● R 211.1 «Unterbau und Schotter»,Bau GD, Bern 1997

SBB Manuals

● Grünflächen bei Bahnanlagen,Handbuch für die Projektierung,Baudirektion SBB, Bern 1994

● Grünflächen bei Bahnanlangen,Handbuch für den Unterhalt, SBB AG,I-AM-EB-U, Bern 2001

VSS standards

● SN 640 431b – Asphaltbetonbeläge,VSS, Zürich 1997

● SN 671 560 – Unterhalt derGrünflächen an Bahnanlagen,VSS, Zürich 1998

SAEFL environment literature

● Christian Müller, AusgewählteVerfahren zur Vegetationskontrolle aufBahnanlagen, Umwelt-Materialien no. 108, BUWAL, Bern 1999

Glossary

Ballast/ballast bed Small blocks of stone made from unweathered and extremely hard rock that is crushed andscreened. Provides an elastic basis for the track panel and allows adjustments of the track levelto be made during maintenance work.

Bank Bank is the term used to describe the areas of greenery along tracks outside the track area.

Bituminous weed barrier Weed barrier made of bitumen or related material as a sub ballast layer. Prime function is toseal off water.

Clay Smallest grain fraction of minerals (grain size < 0.002 mm).

Drainage System/installations to drain water from the bearing layers of the sub- and superstructure.

Embankment shoulder Interface between verge and bank.

Environmental audit Assessment of the environmental impacts and compatibility of a given product.

Environmental compatibility Assessment of the environmental consequences of any action.

Extensive maintenance zone Area more than 5 metres from the track centre, where maintenance measures are determinedaccording to the type of vegetation present or desired (as well as according to safetyconsiderations). Roughly equivalent to the bank.

Glyphosate Systemic leaf herbicide with excellent effect against most plant species.

Gravel sand Frost-proof, compressible mineral material consisting of fine grains of stone of varying sizes,evenly distributed. SBB uses grade 1, SBB or 125 gravel sand.

Green area map Map or cadastre of the green areas on SBB property along the track, containing data onlocation, existing and preferred condition of vegetation, and applicable maintenance methods.

Groundwater protection zones Areas where ground water is stored and/or drawn, protected by law.

Herbicide Plant-killing substance.

Humus Sum of all dead and mineralised organic matter in the soil.

Intensive maintenance zone Area up to 5 metres from the track centre, where safety aspects prevail in the choice ofmaintenance methods. Comprises the track area (including verge) and a 1-2 metres widetransition band between verge and bank.

Leaf herbicide Weed killer, absorbed mainly through the leaves, and designed to eliminate the plant.

Local conditions All the environmental conditions characteristic of a plant growth site (weather, situation, soil,etc.).

Minerals Compact or loose rock that forms the solid part of the soil (as opposed to humus).

Mulching Use of mowing machines fitted with a device to spread cuttings thinly over the surface.

Plant families Groups of plants indicative of specific site conditions.

Porous concrete bars Solid verge construction of porous concrete to stabilise the inspection walkway andembankment shoulder whilst preventing plants from growing into the track area from the bank.

Preventive measures Preventive action against undesired vegetation.

Regenerative elements Parts of plants that in favourable conditions can grow up again into complete plants.

Rhizome Perennial, constantly growing root system storing nutrients and producing buds that each yearsend new shoots above ground.

Silicate Mineral from which mineral nutrients are washed out through weathering (e.g. mica, feldspar).

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Silt (coarse clay) Second-smallest grain fraction of minerals (grain size 0.002 - 0.06 mm).

Soil herbicide Weed-killer. The agents that are toxic for the plants are taken up via the soil through the roots.

Spray solution Ready-to-use dilution of weed killer with water.

Stone chippings Broken up mineral matter with a grain size range according to load requirements and conditionof the subgrade.

Storage system Plant parts like beets, tubers, bulbs, rhizomes and the cotyledons of seeds that are used for thetemporary storage of nutrients such as carbohydrates, fats, proteins, etc.

Substructure Bearing layers between the ballast bed and the surface of natural subsoil.

Sulphosate Leaf herbicide with almost the same effect as Glyphosate.

Symptoms, treatment of Removal of existing undesired vegetation.

Synergies Reinforcement of the effect of a single measure through a joint effect of two or severalvegetation control methods.

Transition band Part of the bank adjacent to the verge in the intensive maintenance area.

Tuber see storage systems

Vegetation type Division of vegetation according to structural features and plant composition (woodland,meadow, etc.).

Vegetation control Control of vegetation growing on or near the railway tracks using a combination of differentmethods.

Verge Lateral stabilisation structure adjacent to the ballast bed. It serves the staff as inspectionwalkway. The minimum width of an accessible verge is generally between 0.6 and 0.9 metres. Toensure good drainage, it must be built using permeable, large-grained material (SBB regulationsR 211.1).

Woodland Woody vegetation, as opposed to grassland.

Basic and further education possibilities

Specialist licence for the use of plant treatment substancesin the maintenance of railway tracks and grounds.Regular courses given by the Swiss Training Centre for nature and the protection of theenvironment (SANU) in Biel Switzerland, commissioned by the Swiss Agency for theEnvironment, Forests and Landscape. The objective of the course is to issue thecorresponding licence.

Further information:Telephone: 032 322 14 33Fax: 032 322 13 20E-Mail: sanu@sanu.chInternet: www.sanu.ch

Information

SBB AG, Bern (Swiss Federal Railways)Rail Environmental CenterParkterrasse 14CH-3000 Bern 65, SwitzerlandTelephone ++41 (0)512 20 58 19Fax ++41 (0)512 20 44 75E-Mail umwelt@sbb.chInternet www.sbb.ch

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