70676 Transport Engineering
CIV3703 Transport Engineering
Source: Austroads
Module 3, Part 2 Geometric design of roads
Part 2: 3.7 Width of Traffic Lanes and Carriageway
3.7.1 Factors Affecting Lane Width Lane width based on: Traffic volume Vehicle dimensions Combination of speed and traffic volume
Desirable lane width: 3.5m May use widths as low as 3.0m for low traffic.
3.7.2 Factors Affecting Shoulder Width Shoulder width = edge of traffic lane to edge of usable carriageway. Advantages of wide shoulders: Space for stationary vehicles Emergency are for errant vehicles Driver comfort increased Sight distance improved across horizontal curves
Minimum 1.0m;
Desirable: up to 3m
3.8 Cross Sections ELEMENTS OF A ROAD CROSS SECTION
Catch Drain
Formation Verge
Verge Carriageway Cut Batter
Shoulder
Shoulder Traffic Lanes
Table Drain
Centreline
Fill Batter
3.8.2 Crossfalls - Pavements Type of Pavement
Crossfall %
Earth, Loam
5
Gravel
4
Bituminous Seal Coat
3
Asphalt Portland Cement Concrete
2.5 – 3 2-3
Crossfalls - Shoulders Type of Shoulder
Crossfall %
Earth, Loam
5 to 6
Gravel
4 to 5
Seal, asphalt or concrete
3 to 4 (same as traffic lanes)
3.8.3 Drains – Table Drains Located on outside of shoulders in cuttings Invert level below pavement subgrade level Longitudinal grade > 5% lining necessary (scour) Longitudinal grade < 0.5% - lining (siltation) Side slope – desirable max. 6 to 1
Catch Drains Located on high side of cutting batters 2m behind edge of batter
3.8.4 Batters Cuts Shallow cuts: flatten batters Rock cuts: max 0.25 horizontal to 1 vertical Other cuts: generally 1.5 or 2 to 1
Fills Generally max 1.5 to 1 Steep slopes may be used with rock facing To account for out of control vehicles use slopes less than 4 to 1.
3.9 Sight Distance Driver should be able to see any possible road hazard in time to take evasive action. This forms basis of sight distance considerations.
Sight distance based on number of assumptions.
Sight Distance
Sight Distance Assumptions Height of Eye - Car 1.05 m - Truck 2.4 m Height of Object - Approaching vehicle 1.25 m - Object on road 0.2 m - Tail light / stop light 0.6~0.8 m Reaction time 2.5 seconds
3.9.2 Stopping Sight Distance Driver travelling at design speed sees object and decides to stop. During decision time, travel distance: = Rt.v where Rt = reaction time (2.5 sec) v = initial speed of vehicle (m/s)
Driver then brakes and decelerates from design speed to zero.
Travel distances: v2 / 2g(d + 0.01a) Where: v = initial speed of vehicle (m/s) g = acceleration due to gravity d = coefficient of longitudinal deceleration a = longitudinal grade (% + for upgrade and – for downgrades)
Stopping Sight Distance Formula
Stopping Sight Distances for cars Design Speed (kph)
Stopping Sight Distance (d = 0.36, a = 0%) Normal Design (2.5 secs)
(2.0 secs)
Restricted (1.5 secs)
60
81
73
65
80
126
114
100
179
120
241
130
275
3.9.3 Overtaking Requirements Overtaking action – large number of vehicles: Judgment of overtaking driver Risks driver is willing to take Speed of vehicles Size of vehicles Actions of driver being overtaken Actions of other drivers not involved in overtaking.
Basic Needs for Sight Distance Establishment Sight Distance Certain sight distance needed to compete an overtaking manoeuvre feasible.
Continuation Sight Distance Once commenced, a certain sight distance needed to continue overtaking.
Assumptions in Deriving Values Sight distance derived from time gap which driver will accept. Overtaking and oncoming vehicles both at operating speed. Overtaken vehicle at a less speed taken as mean speed of its direction of travel. Height of eye & object both 1.05 m.
Overtaking Sight Distances Establishment
Continuation
S.D. (m)
S.D. (m)
50
490
260
80
59
610
320
90
67
740
370
100
76
890
450
110
84
1070
540
Design Speed (kph)
Overt. Speed (kph)
70
3.10 Vertical Curves Longitudinal Profile: section along centreline of road. Straight grades joined by vertical curves. Curves used to smooth passage of vehicles from one grade to the next. Also to provide appropriate sight distance. Convex: summit or crest; concave or sag
Length of Vertical Curves Crest curves Stopping sight distance, or Appearance
Sag curves Comfort for vertical acceleration Appearance Other: drainage; headlight performance; overhead restrictions.
Curve Forms: Various – parabola common.
Notations
Calculation of Points on a Vertical Curve
𝑀𝑖𝑑 − 𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒, 𝑒 = y= 𝐾=
𝑒 𝑋2 𝐿 2 2 𝐿 𝐴
𝐿 (𝑔1 800
− 𝑔2 )
where: A = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑔𝑟𝑎𝑑𝑒 % = (𝑔1 − 𝑔2 )
Calculation of Vertical Curve Length Governing value is K where K = Length of Vertical curve for 1% change in grade i.e. K = L / A where L = length of vertical curve A = algebraic change of grade
Minimum length of crest vertical curves
Minimum length of sag vertical curves
3.11 Grades High speed roads – grades up to 3% good. More modest design speeds – grades up to 6% usually cause little problem. Gradients >10% create problems of slow climbing speeds, and potentially high downhill speeds.
General Maximum Grades Design Speed (kph)
Terrain Flat
Rolling
Mountain.
60
7
8
10*
80
5
6
8
100
4
5
7
120
4
5
* Grades over 10% should be used with caution.
Grades Steeper Than General Maximum Used: Relatively short sections Difficult terrain where general maximums not practicable Number of heavy vehicles low.
Low volume roads: 12 to 15% No commercial vehicles: up to 33%
3.12 Design Form Traditional road design – series of two dimensional views. Gives poor results if each view considered independently. Need to design road from user’s perspective.
Design Points Horizontal and vertical sight distances must be considered together. Each may be adequate but in combination they may be deficient. Horizontal and vertical curves should be kept in phase. Vertical curves contained in horizontal.
End of Module 3, Part 2
Source: Austroads
Module 3, Part 2 Geometric design of roads
Part 2: 3.7 Width of Traffic Lanes and Carriageway
3.7.1 Factors Affecting Lane Width Lane width based on: Traffic volume Vehicle dimensions Combination of speed and traffic volume
Desirable lane width: 3.5m May use widths as low as 3.0m for low traffic.
3.7.2 Factors Affecting Shoulder Width Shoulder width = edge of traffic lane to edge of usable carriageway. Advantages of wide shoulders: Space for stationary vehicles Emergency are for errant vehicles Driver comfort increased Sight distance improved across horizontal curves
Minimum 1.0m;
Desirable: up to 3m
3.8 Cross Sections ELEMENTS OF A ROAD CROSS SECTION
Catch Drain
Formation Verge
Verge Carriageway Cut Batter
Shoulder
Shoulder Traffic Lanes
Table Drain
Centreline
Fill Batter
3.8.2 Crossfalls - Pavements Type of Pavement
Crossfall %
Earth, Loam
5
Gravel
4
Bituminous Seal Coat
3
Asphalt Portland Cement Concrete
2.5 – 3 2-3
Crossfalls - Shoulders Type of Shoulder
Crossfall %
Earth, Loam
5 to 6
Gravel
4 to 5
Seal, asphalt or concrete
3 to 4 (same as traffic lanes)
3.8.3 Drains – Table Drains Located on outside of shoulders in cuttings Invert level below pavement subgrade level Longitudinal grade > 5% lining necessary (scour) Longitudinal grade < 0.5% - lining (siltation) Side slope – desirable max. 6 to 1
Catch Drains Located on high side of cutting batters 2m behind edge of batter
3.8.4 Batters Cuts Shallow cuts: flatten batters Rock cuts: max 0.25 horizontal to 1 vertical Other cuts: generally 1.5 or 2 to 1
Fills Generally max 1.5 to 1 Steep slopes may be used with rock facing To account for out of control vehicles use slopes less than 4 to 1.
3.9 Sight Distance Driver should be able to see any possible road hazard in time to take evasive action. This forms basis of sight distance considerations.
Sight distance based on number of assumptions.
Sight Distance
Sight Distance Assumptions Height of Eye - Car 1.05 m - Truck 2.4 m Height of Object - Approaching vehicle 1.25 m - Object on road 0.2 m - Tail light / stop light 0.6~0.8 m Reaction time 2.5 seconds
3.9.2 Stopping Sight Distance Driver travelling at design speed sees object and decides to stop. During decision time, travel distance: = Rt.v where Rt = reaction time (2.5 sec) v = initial speed of vehicle (m/s)
Driver then brakes and decelerates from design speed to zero.
Travel distances: v2 / 2g(d + 0.01a) Where: v = initial speed of vehicle (m/s) g = acceleration due to gravity d = coefficient of longitudinal deceleration a = longitudinal grade (% + for upgrade and – for downgrades)
Stopping Sight Distance Formula
Stopping Sight Distances for cars Design Speed (kph)
Stopping Sight Distance (d = 0.36, a = 0%) Normal Design (2.5 secs)
(2.0 secs)
Restricted (1.5 secs)
60
81
73
65
80
126
114
100
179
120
241
130
275
3.9.3 Overtaking Requirements Overtaking action – large number of vehicles: Judgment of overtaking driver Risks driver is willing to take Speed of vehicles Size of vehicles Actions of driver being overtaken Actions of other drivers not involved in overtaking.
Basic Needs for Sight Distance Establishment Sight Distance Certain sight distance needed to compete an overtaking manoeuvre feasible.
Continuation Sight Distance Once commenced, a certain sight distance needed to continue overtaking.
Assumptions in Deriving Values Sight distance derived from time gap which driver will accept. Overtaking and oncoming vehicles both at operating speed. Overtaken vehicle at a less speed taken as mean speed of its direction of travel. Height of eye & object both 1.05 m.
Overtaking Sight Distances Establishment
Continuation
S.D. (m)
S.D. (m)
50
490
260
80
59
610
320
90
67
740
370
100
76
890
450
110
84
1070
540
Design Speed (kph)
Overt. Speed (kph)
70
3.10 Vertical Curves Longitudinal Profile: section along centreline of road. Straight grades joined by vertical curves. Curves used to smooth passage of vehicles from one grade to the next. Also to provide appropriate sight distance. Convex: summit or crest; concave or sag
Length of Vertical Curves Crest curves Stopping sight distance, or Appearance
Sag curves Comfort for vertical acceleration Appearance Other: drainage; headlight performance; overhead restrictions.
Curve Forms: Various – parabola common.
Notations
Calculation of Points on a Vertical Curve
𝑀𝑖𝑑 − 𝑜𝑟𝑑𝑖𝑛𝑎𝑡𝑒, 𝑒 = y= 𝐾=
𝑒 𝑋2 𝐿 2 2 𝐿 𝐴
𝐿 (𝑔1 800
− 𝑔2 )
where: A = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑔𝑟𝑎𝑑𝑒 % = (𝑔1 − 𝑔2 )
Calculation of Vertical Curve Length Governing value is K where K = Length of Vertical curve for 1% change in grade i.e. K = L / A where L = length of vertical curve A = algebraic change of grade
Minimum length of crest vertical curves
Minimum length of sag vertical curves
3.11 Grades High speed roads – grades up to 3% good. More modest design speeds – grades up to 6% usually cause little problem. Gradients >10% create problems of slow climbing speeds, and potentially high downhill speeds.
General Maximum Grades Design Speed (kph)
Terrain Flat
Rolling
Mountain.
60
7
8
10*
80
5
6
8
100
4
5
7
120
4
5
* Grades over 10% should be used with caution.
Grades Steeper Than General Maximum Used: Relatively short sections Difficult terrain where general maximums not practicable Number of heavy vehicles low.
Low volume roads: 12 to 15% No commercial vehicles: up to 33%
3.12 Design Form Traditional road design – series of two dimensional views. Gives poor results if each view considered independently. Need to design road from user’s perspective.
Design Points Horizontal and vertical sight distances must be considered together. Each may be adequate but in combination they may be deficient. Horizontal and vertical curves should be kept in phase. Vertical curves contained in horizontal.
End of Module 3, Part 2
