Road Design Aspect

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ROAD DESIGN ASPECTSFOR TRAFFIC SAFETY

Dr. Ir. Sigit Priyanto, M.ScJan 2008

Master Program in Transportation System and Engineering

Gadjah Mada University


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Aspect to Road Design

1. Road Geometry

adequate sight distance

adequate road lamp

2. Pavement and Drainage

good skid resistance texture

adequate drainage ditch


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Design Process


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When roads are rehabilitated or new road are

being built, specific effort are made to

minimize the disbenefits to communities

along the road so that through traffic as it

passes through the community, does notcause problems or dangers to pedestrians

and local traffic

Problem:

1. Traffic conflict between mayor

road and minor road2. Conflict between pedestrian

and vehicle, caused by high

speed

High speed interurban traffic causes

danger to pedestrians and local traffic

as it passes through small

communities

Existing interurban road results in

considerable conflict between

through traffic and local traffic


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Solution:BYPASS


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SPEED DESIGN

Involved by:

1. Vehicle Type and Condition2. Driver Characteristic

3. Road Geometry

4. Other vehicle speed

5. Speed Control

Problem:

Relationship between speed, geometry and accidentsare generally poorly understood, and the effects of

intersection between different design features is difficultto predict: e.g. is a straight narrow road more or lesssafe than a tortuous but wide road?


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Design class standards are used

which link road function, traffic flow

and geometry in order to develop an

economic design. Consistency is

ensured by comparing estimates of

actual speeds with those inherent in

each of the design class standards.

If the design is found to be

inadequate on the basis of this

comparison, a new alignment is

adopted and the process repeated

Schematic relationship betweenspeed horizontal curvature


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Solution

1. Use comprehensive

design standard

2. Estimate the

reduction of free flow

speed which is

caused by road wide,

type, and road

condition


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Design to Sight Distance

Sight distance involved by:

1. Vehicle speed2. Assume drivers eye

3. Object height

- Poor sight distance

- Note also U-type drain whichposes potential hazard


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Solution

Good sight

distance in Kenya


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Horizontal Curvature

Horizontal Curvature Design :

1. Radius Curve

2. Speed

3. Road Marking

4. Warning Device

Design Speed / curvature relationshipDesign speed and friction factors


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- There are two type of vertical curve: sag curve and crest curve

sag curve

crest curve

- Design of vertical curve based on

sight distance for comfort and

parabolic function which is used

to connect the gradient

- Poor visibility due to sag curve in

Papua New Guinea

Vertical Curves


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Roller Coaster Road

in Papua New Guinea

Solution:

Determine the minimum

value based on design

speed and the number of

lane


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Horizontal and vertical

alignments should not beconsidered

independently

Examples of bad

combinations of

horizontal and vertical

curvature

Combination of Horizontal/Vertical Curves


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Good coordination

between vertical and

horizontal alignment

Example:Good coordination between

vertical and horizontal

alignment in Korea

(adequate sight distance and

consistent)


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Simple circular horizontal curve are normally used for

road design. In order to facilitate the gradual transitionof steering from straight section of road to the curves,

transition curves are often provided. The characteristic

of a transition curve is that it has a constantly reducing

radius, as in a spiral

Super elevation is often applied over the length of a

circular curve to reduce a sideway frictional

requirement between the tyres and road surface andto increase comfort. In such situations, the transition

curve length may be used to introduce the super

elevation

The widening of traffic lane is often necessary on

lower radius curves o allow for the offset of the rear

axles of heavy vehicles following a smaller radiuscurve than the steering axle

Superelevation design curve

Transition Curve, Superelevation and Pavement Widening

Horizontal Curve

Vertical Curve


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Solutions:

- A maximum superelevation of 8 or 10 %

will generally eliminate overturning and

sliding problem

- The length of a translation curve should

be the sum of the length required to

remove adverse chamber and the

length needed to increase this crossfall

to the full superelevation requirement

- Drainage conditions should be checkedto ensure that combinations of fall along

and across the road are adequate to

remove water from potential flat areas

- Increase width over a complete section

to offer a more consistent aspect todriver

Superelevation on road in Papua New

Guinea


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Gradient and Criteria for Climbing Lanes

- Danger for heavy vehicle

- Ineffective and not economical

- Gradient Design

- Estimate speed increase with

climbing lane


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Solution:

Clear signal, marking and barrier

Climbing lane start before thegradient and end after it

Consider the contra flow

Additional climbing lane in Papua

New Guinea


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Generally, consist of shoulder or kerbs, carriageway,

drainage features, and earthwork profile May also include facilities for pedestrians, cyclists or

other specialist user groups

Cross sections types in urban area

Cross Section


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Not uniform (danger for accident and

erosion)

Drainage facility is not available

Problem

Solutions

Uniform elevation

Clear marking

Use the barrier to separate drainage and

shoulder

Slope is less than :6 (1:10 in flat to rolling

terrain and 1:4 in mountainous terrain) Adequate space in shoulder to turning,

parking, or maneuver

Severe unprotected side

slopes being surveyed

Road with shallow slide slope


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Drainage

Drainage ditches must, first and foremost,

be design to accommodate the expected

rainfall and run-off and are required toprevent structural damage to the road

Problem

- Pedestrian facility is not available, causepedestrian walk in drainage ditch as

shown in figure 1

- Separated block is not available between

road and drainage ditch cause vehicle

cause potential hazards for traffic as

shown in figure 2

- In adequate drainage ditch

Figure 1

Figure 2


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Solutions:

- Hydrological study must be made using

all available data, including discussions

with local inhabitants, aerial photographsof areas upstream and personal

reconnaissance

- Culvert are required to reduce the risk of

flow damaging the roadside ditches

- Use drainage type I and J than U and V

Note:

- Picture 1. Shallow slope to drainagechannel gives room for recovery in Kenya

- Picture 2. Covering drainage channels as

in Thailand can reduce the risk of

accidents

Picture 1

Picture 2


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Overtaking Zones

Overtaking is an inherently dangerous maneuver, especially on single

carriageway roads where it creates the potential for head on collisions

Problem in developing countries:

- In adequate space to overtaking

- Unclear marking

- Sign is not provided

- Not well maintained

Dangerous overtaking on a steep

winding in Indonesia with many

HGVs and buses but no clawler

lane


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Solution:

- Adequate space for overtaking (such as:

more lane in overtaking area as shown in

Figure 2- Clear marking

- Traffic sign installation

- Adequate road length for overtaking as

shown in Figure 1

Figure 1 Figure 2


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Skidding is a contributory factor in

many accidents, particularly on wetroads on the approach to intersection

Problem:

There is frequently a lack of standardslaid down for road surface texture.

Often good quality aggregates and

binders are not readily available and

inadequate materials are used

Even where abrasion and resistance topolishing criteria have been considered

in the design procedure, they are often

not give the importance they deserve in

maintenance activities

Aggregate Texture

Pavement Aspect

Rough

Rough

Smooth

Smooth

Harsh

Harst

Poli

shed

Poli

shed

A

B

C

D


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Solution:

- Choose good skid resistance texture

- Skid resistance measurement in field


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Road Construction Aspects

1. Sign and MarkingUsed to show that this area is under constructing

2. Sign Lampif must available, sign used must clear

3. Other Equipment

Special clothes for worker, traffic cone, etc.

Safer Road Works Ahead Video
http://localhost/var/www/apps/conversion/releases/20121107221618/tmp/scratch_5/geometri%20thdp%20keselamatan.DAT


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THANK YOU

Road Design Aspect

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