Chapter 3: Width for Turning Roadways at Chapter 3: Width for Turning Roadways at Intersections and Sight Distance on H-Intersections and Sight Distance on H-

Curves (p. 3-97 - 3-112)Curves (p. 3-97 - 3-112)

Be able to explain the differences among the three Be able to explain the differences among the three cases used for determining turning roadway width cases used for determining turning roadway width at intersectionsat intersectionsBe able to explain the differences among the three Be able to explain the differences among the three different traffic conditions used for adjusting turning different traffic conditions used for adjusting turning roadway widthroadway widthBe able to determine turning roadway width for Be able to determine turning roadway width for different case and traffic condition combinations different case and traffic condition combinations and know how to adjust the width for different types and know how to adjust the width for different types of shouldersof shouldersBe able to determine whether SSD is available on Be able to determine whether SSD is available on horizontal curveshorizontal curves

Objectives:

Moark Junction RT roadways?Moark Junction RT roadways?

Determine the width of the right turn roadway.

Width for Turning Roadways at Width for Turning Roadways at Intersections (p.3-97)Intersections (p.3-97)

The width of turning roadways at The width of turning roadways at intersections are governed by intersections are governed by the types of the types of vehiclesvehicles to be accommodated, to be accommodated, the radius of the radius of curvaturecurvature, and , and the expected speedthe expected speed..

The radius of curvature in combination with The radius of curvature in combination with the track width of the design vehicle the track width of the design vehicle determine the width of a turning roadway. determine the width of a turning roadway. (Then, where does the expected speed come in for determining the (Then, where does the expected speed come in for determining the width?)width?)

3.3.11 Three Operational Cases of Turning 3.3.11 Three Operational Cases of Turning RoadwaysRoadways

Case ICase I: One-lane, one-way operation with no provision : One-lane, one-way operation with no provision for passing a stalled vehicle for passing a stalled vehicle Appropriate for minor Appropriate for minor turning movements and moderate turning volumesturning movements and moderate turning volumes

Three Operational Cases of Three Operational Cases of Turning Roadways (2)Turning Roadways (2)

Case IICase II: One-lane, one-way operation with provision for passing a : One-lane, one-way operation with provision for passing a stalled vehicle stalled vehicle Typical case for ramps and connections at Typical case for ramps and connections at channelized intersections. Note that the Case II widths for large channelized intersections. Note that the Case II widths for large design vehicles are large; hence Case I widths may be used if the design vehicles are large; hence Case I widths may be used if the number of large vehicles is low.number of large vehicles is low.

Three Operational Cases of Three Operational Cases of Turning Roadways (3)Turning Roadways (3)

Case IIICase III: Two-lane operation, either one- : Two-lane operation, either one- or two-way or two-way

Case I and Case IICase I and Case II

Figure 3-21

Case IIICase III

Figure 3-21

Table 3-28b

GB2011:Table 3-28B, p.3-101GB2011:Table 3-28B, p.3-101(Note: WB-50 does not exist in this table anymore)(Note: WB-50 does not exist in this table anymore)

Design Values (p.3-101 ~ 3.104)Design Values (p.3-101 ~ 3.104)

Width values in Table 3-Width values in Table 3-28B) are adjusted for 28B) are adjusted for various traffic conditions various traffic conditions because practically no because practically no turning roadway will serve turning roadway will serve only one type of vehicle. So only one type of vehicle. So traffic condition factor is traffic condition factor is introduced.introduced.

– Traffic condition A: Traffic condition A: Consists of predominantly Consists of predominantly of P vehicles, but some of P vehicles, but some consideration is given to consideration is given to SU (SU-30) trucksSU (SU-30) trucks

– Traffic condition B: Traffic condition B: Sufficient SU (SU-30) Sufficient SU (SU-30) trucks to govern design, trucks to govern design, but some consideration is but some consideration is given to tractor-semitrailer given to tractor-semitrailer combination trucks. 5 to combination trucks. 5 to 10% trucks.10% trucks.

– Traffic condition C: Traffic condition C: Sufficient tractor-semitrailer Sufficient tractor-semitrailer combination trucks, WB-40 combination trucks, WB-40 or WB-50 (WB-40), to or WB-50 (WB-40), to govern design. More trucks govern design. More trucks than condition B.than condition B.

The combination of letters, such as P-SU means that the design width in this example allows a P design vehicle to pass a stalled SU design truck or vice versa.

Larger vehicles that can be accommodated by the widths meant for the combinations in the first table are shown in this table. Safety is maintained as long as they travel at lower speed and the drivers are more cautious and skilled.

+-----+-----

Example (p.3-105): Case II and the traffic volume includes 10 to 12% trucks with an occasional large semitrailer combination for which Traffic Condition C is applicable. With a radius of 165 ft for the inner edge of the traveled way, what would be the width of this turning roadway? With a 4-ft stabilized shoulder? With a vertical curb?

Tab. 3-29

Widths Outside Traveled Way (p.3-105)Widths Outside Traveled Way (p.3-105)

The roadway width for a turning roadway includes the shoulders or equivalent lateral The roadway width for a turning roadway includes the shoulders or equivalent lateral clearance outside the traveled way.clearance outside the traveled way.

– Within a channelized intersection, shoulders for turning roadways are usually unnecessary (often Within a channelized intersection, shoulders for turning roadways are usually unnecessary (often the lanes may be defined by curbs)the lanes may be defined by curbs)

– When there is a separate roadway for right turns, Its left edgeWhen there is a separate roadway for right turns, Its left edge defines one side of the triangular defines one side of the triangular island when the turning radius is small. The side of the island may be defined by other delineators island when the turning radius is small. The side of the island may be defined by other delineators when the turning radius is large. Hence, a developed left shoulder is not necessary.when the turning radius is large. Hence, a developed left shoulder is not necessary.

– A shoulder usually provided on the right side of a right-turning roadway in A shoulder usually provided on the right side of a right-turning roadway in rural areasrural areas. In urban . In urban areas, the right edge may be defined by curbs (because of low speeds). But recommended to areas, the right edge may be defined by curbs (because of low speeds). But recommended to avoid curbs near high-speed highways.avoid curbs near high-speed highways.

– When a turning roadway has large curvature and length and away from other roadways, it is When a turning roadway has large curvature and length and away from other roadways, it is recommended to have a shoulder on both sides.recommended to have a shoulder on both sides.

Tab. 3-30

3.3.12 Sight Distance on Horizontal Curves 3.3.12 Sight Distance on Horizontal Curves (p.3-106)(p.3-106)Where there are sight Where there are sight

obstructions on the inside of obstructions on the inside of curves or the inside of the curves or the inside of the median lane on divided median lane on divided highways, a design may need highways, a design may need adjustment in the normal adjustment in the normal highway cross section or highway cross section or change in the alignment if change in the alignment if removal of the obstruction is removal of the obstruction is impractical.impractical.

The sight line is a chord of the The sight line is a chord of the curve, and the stopping sight curve, and the stopping sight distance is measured along the distance is measured along the centerline of the inside lane centerline of the inside lane around the curve.around the curve.

R

S

R

s

65.281802

Figure 3-23

ɵR

s

22

360

Criteria for Measuring Sight DistanceCriteria for Measuring Sight Distance

Height of driver’s eyeHeight of driver’s eye– 3.5 ft from the pavement 3.5 ft from the pavement

surfacesurface

Height of objectHeight of object– For SSD = 2.0 ftFor SSD = 2.0 ft– For PSD = 3.5 ftFor PSD = 3.5 ft

Sight obstructionsSight obstructions– On horizontal curves On horizontal curves the the

road surface on a crest road surface on a crest curve, or something curve, or something outside the traveled way, outside the traveled way, such as a longitudinal such as a longitudinal barrier, the backslope of a barrier, the backslope of a curve section, a tree, etc.curve section, a tree, etc.

2.75 ft for SSD

3.5 ft for PSD Figure 3-22b

3.3.13 General Controls for Horizontal Alignment 3.3.13 General Controls for Horizontal Alignment (p.3-111): Read this page carefully. (p.3-111): Read this page carefully.

Alignment should be as directional as practical.Alignment should be as directional as practical.

The minimum radius of curvature for that should be avoided wherever The minimum radius of curvature for that should be avoided wherever practical.practical.

Consistent alignment should always be sought. Sharp curves should Consistent alignment should always be sought. Sharp curves should not be introduced at the ends of long tangents.not be introduced at the ends of long tangents.

For small deflection angles, curves should be sufficiently long to avoid For small deflection angles, curves should be sufficiently long to avoid the appearance of a kink.the appearance of a kink.

Sharp curvature should be avoided on long, high fills.Sharp curvature should be avoided on long, high fills.

Caution should be exercised in the use of compound circular curves.Caution should be exercised in the use of compound circular curves.

Abrupt reversals in alignment should be avoided.Abrupt reversals in alignment should be avoided.

The “broken-back” or “flat-back” arrangement of curves should be The “broken-back” or “flat-back” arrangement of curves should be avoided unless absolutely needed.avoided unless absolutely needed.

To avoid the appearance of inconsistent distortion, the horizontal To avoid the appearance of inconsistent distortion, the horizontal alignment should be coordinated carefully with the profile design.alignment should be coordinated carefully with the profile design.

Changing median widths on tangent alignment should be avoided, Changing median widths on tangent alignment should be avoided, where practical, so as not to introduce a distorted appearance.where practical, so as not to introduce a distorted appearance.

Do You Remember? Do You Remember? Geometry of horizontal curves (Review Geometry of horizontal curves (Review what you learned in the survey class.)what you learned in the survey class.)

1

2cos

1

2sec

2sin2

2tan

R

RRE

RLC

RT

2cos1

2cos

R

RRM

DL

RD

D

R

RL

100

6.57293602

'100180

Setting out of a simple horizontal curveSetting out of a simple horizontal curve

Usually PI is given:

First find the station of PC Subtract T from the station of PI

Then find the next whole station from PC. Compute l1 to find 1.

Then find D for L = 100 ft

Then find the left over of the curve length l2 to determine the station of PT

T

2

2

1

1

lLl

2

sin2

2sin2

2sin2

22

11

RC

DRC

RC

D

l1 & l2 are along the curve.

You need the chord length to place stakes.

2tan

RT