1. Geometric Design It deals with visible elements of a highway.
It is influenced by:
Nature of terrain.
Type
Composition and hourly volume / capacity of traffic
Traffic Factors
Operating speed (Design Speed)
Landuse characteristics (Topography)
Environmental Factors (Aesthetics).

2. TERRAIN CLASSIFICATION
Terrain type
Percentage cross slope
of the country
Plain
0-10
Rolling
10-25
Mountainous
25-60
Steep
>60

3. goals of geometric design
Maximize the comfort
Safety,
Economy of facilities
Sustainable Transportation Planning.

4. FUNDAMENTALS OF GEOMETRIC DESIGN
geometric cross section
vertical alignment
horizontal alignment
super elevation
intersections
various design details.

5. HIGHWAY GEOMETRIC DESIGN
Cross sectional elements
Sight distance
Horizontal curves
Vertical curves

6. Comparision of Urban and Rural Roads
Section Capacity
Peak Hour flow
Traffic fluctuations
Design Based on ADT
Speed

7. Urban Road Classification
ARTERIAL ROADS
SUB ARTERIAL
COLLECTOR
LOCAL STREET
CUL-DE-SAC
PATHWAY
DRIVEWAY

8. Urban Road Classification
ARTERIAL ROADS
SUB ARTERIAL
COLECTOR
LOCAL STREET
CUL-DE-SAC
PATHWAY
DRIVEWAY

11. ARTERIAL
No frontage access, no standing vehicle, very little cross traffic.
Design Speed : 80km/hr
Land width : 50 – 60m
Spacing 1.5km in CBD & 8km or more in sparsely developed areas.
Divided roads with full or partial parking
Pedestrian allowed to walk only at intersection

12. SUB ARTERIAL Bus stops but no standing vehicle.
Less mobility than arterial.
Spacing for CBD : 0.5km
Sub-urban fringes : 3.5km
Design speed : 60 km/hr
Land width : 30 – 40 m

13. Collector Street Collects and distributes traffic from local streets
Provides access to arterial roads
Located in residential, business and industrial areas.
Full access allowed.
Parking permitted.
Design speed : 50km/hr
Land Width : 20-30m

14. Local Street Design Speed : 30km/hr. Land Width : 10 – 20m.
Primary access to residence, business or other abutting property
Less volume of traffic at slow speed
Origin and termination of trips.
Unrestricted parking, pedestrian movements. (with frontage access, parked vehicle, bus stops and no waiting restrictions)

15. CUL–DE- SAC
Dead End Street with only one entry access for entry and exit.
Recommended in Residential areas

16. HIGHWAY CROSS SECTIONAL ELEMENTS
1.Carriage way (Pavement width)
2.Camber
3.Kerb
4.Traffic Separators
5.Width of road way or formation width
6.Right of way (Land Width)
7.Road margins
8.Pavement Surface
(Ref: IRC 86 – 1983)

17. GEOMETRIC CROSS SECTION
The primary consideration in the design of cross sections is drainage.
Highway cross sections consist of traveled way, shoulders (or parking lanes), and drainage channels.
Shoulders are intended primarily as a safety feature.
Shoulders provide:
accommodation of stopped vehicles
emergency use,
and lateral support of the pavement.
Shoulders may be either paved or unpaved.
Drainage channels may consist of ditches (usually grassed swales) or of paved shoulders with berms of curbs and gutters.

18. Two-lane highway cross section, with ditches.
Two-lane highway cross section, curbed.
Two-lane highway cross section, with ditches.
Two-lane highway cross section, curbed.

19. Divided highway cross section, depressed median, with ditches.

20. Geometric cross section cont..
Standard lane widths are 3.6 m (12 ft).
Shoulders or parking lanes for heavily traveled roads are 2.4 to 3.6 m (8 to 12 ft) in width.
narrower shoulders used on lightly traveled road.

21. CARRIAGE WAY (IRC RECOMMENDATIONS)
Single lane without Kerbs = 3.50m
Two lane without kerbs = 7m
Two lane with kerbs = 7.5m
3 lane with or without kerbs = 10.5 /11.0
4 lane with or without kerbs = 14.0m
6 lane with or without kerbs = 21.0 m
Intermediate carriage way = 5.5m
Multilane pavement = 3.5m/lane

22. Footpath (Side walk) No of Persons/Hr Required Width of footpath (m)
All in one direction
In both direction
1200
800
1.5
2400
1600
2.0
3600
2.5
4800
3200
3.0
6000
4000
4.0

23. Cycle Track Minimum = 2m Each addln lane = 1m
Separate Cycle Track for peak hour cycle traffic more than 400 with motor vehicle of traffic 100 – 200 vehicles/Hr.
Motor Vehicles > 200; separate cycle track for cycle traafic of 100 is sufficient.

24. Median Width of Median Depends on: Mim Width of Median: Available ROW
Terrain
Turn Lanes
Drainage.
Mim Width of Median:
Pedestrian Refuge =1.2m
To protect vehicle making Right turn = 4.0m (Recc – 7.0m)
To protect vehicle crossing at grade = 9 – 12m.
For Urban area 1.2 to 5m

25. KERBS Road kerbs serve a number of purposes:
- retaining the carriageway edge to prevent 'spreading' and loss of structural integrity
- acting as a barrier or demarcation between road traffic and pedestrians or verges
- providing physical 'check' to prevent vehicles leaving the carriageway
- forming a channel along which surface water can be drained

26. KERBS
Low or mountable kerbs : height = 10 cm provided at medians and channelization schemes and also helps in longitudinal drainage.
Semi-barrier type kerbs : When the pedestrian traffic is high.
Height is 15 cm above the pavement edge.
Prevents encroachment of parking vehicles, but at acute emergency it is possible to drive over this kerb with some difficulty.
Barrier type kerbs : Designed to discourage vehicles from leaving the pavement. They are provided when there is considerable amount of pedestrian traffic.
Height of 20 cm above the pavement edge with a steep batter.
Submerged kerbs :
They are used in rural roads.
The kerbs are provided at pavement edges between the pavement edge and shoulders.
They provide lateral confinement and stability to the pavement.

27. CAMBER (OR) CROSS FALL S. No Type of Surface
% of camber in rainfall range Heavy to light 1
Gravelled or WBM surface
2.5 % - 3 %
( 1 in 40 to 1 in 33) 2
Thin bituminous Surface
2.0 % %
( 1 in 50 to 1 in 40) 3
Bituminous Surfacing or Cement Concrete surfacing
1.7 % % 4
Earth
4 % - 3 %

28. Types of Camber Parabolic or Elliptic Straight Line
Straight and Parabolic

29. Sight Distances
The actual distance along the road surface up to which the driver of a vehicle sitting at a specified height has visibility of any obstacle.
The visibility ahead of the driver at any instance. 29

30. SIGHT DISTANCE
THE SIGHT DISTANCE AVAILABLE ON A ROAD TO A DRIVER DEPENDS ON
FEATURE OF ROAD AHEAD
HEIGHT OF THE DRIVER’S EYE ABOVE THE ROAD SURFACE

31. Sight Distances 1. Stopping Sight distance
2. Over Taking Sight distance
3. Passing
4. Intermediate 31

32. Sight Distance in Design
Stopping Sight Distance (SSD) – object in roadway
Passing Sight Distance (PSD) – pass slow vehicle 32

33. Stopping Sight Distance (SSD)
THE DISTANCE WITHIN WHICH A MOTOR VEHICLE CAN BE STOPPED DEPENDS ON
Total reaction time of driver
Speed of vehicles
Efficiency of brakes
Gradient of road
Frictional resistance

34. TOTAL REACTION TIME
PERCEPTION TIME
BRAKE REACTION TIME

35. TOTAL REACTION TIME DEPENDS ON PIEV THEORY
PERCEPTION
INTELLECTION
EMOTION
VOLIATION

36. Perception-Reaction Process
Identification
Emotion
Reaction (volition)
PIEV
Used for Signal Design and Braking Distance 36 36

37. Perception-Reaction Process
Sees or hears situation (sees deer)
Identification
Identify situation (realizes deer is in road)
Emotion
Decides on course of action (swerve, stop, change lanes, etc)
Reaction (volition)
Acts (time to start events in motion but not actually do action)
Foot begins to hit brake, not actual deceleration 37 37

38. 0.5 to 7 seconds Affected by a number of factors.
Typical Perception-Reaction
time range
0.5 to 7 seconds
Affected by a number of factors. 38 38

39. Perception-Reaction Time Factors
Environment
Urban vs. Rural
Night vs. Day
Wet vs. Dry
Age
Physical Condition
Fatigue
Drugs/Alcohol
Distractions 39 39

40. Age
Older drivers
May perceive something as a hazard but not act quickly enough
More difficulty seeing, hearing, reacting
Drive slower
Less flexible 40 40

41. Age
Younger drivers
Quick Response but not have experience to recognize things as a hazard or be able to decide what to do
Drive faster
Are unfamiliar with driving experience
Are less apt to drive safely after a few drinks
Are easily distracted by conversation and others inside the vehicle
May be more likely to operate faulty equipment.
Poorly developed risk perception
Feel invincible, the "Superman Syndrome” 41 41

42. Alcohol Affects each person differently Slows reaction time
Increases risk taking
Dulls judgment
Slows decision-making
Presents peripheral vision difficulties 42 42

43. Stopping Sight Distance (SSD)
Required for every point along alignment (horizontal and vertical) – Design for it, or sign for lower, safe speed.
Available SSD = f(roadway alignment, objects off the alignment, object on road)
SSD = LD + BD
Lag distance
Braking Distance 43

44. Lag Distance Speed of the vehicle = v m/sec
Reaction Time of Driver = t sec ; (2.5 sec)
Lag Distance = v t m
If the design speed is V kmph,
Lag Distance = V x x t
60 x 60
= V t m

45. Braking Distance
Kinetic Energy at the design speed of v m/sec= ½ m v2
= W v2 ; m = W/g 2g
W = weight of the Vehicle
G = acceleration due to gravity (9.9 m/sec2)
Work done in stopping the vehicle = F x l
F = Frictional force
L = braking distance
F = coeff of friction = 0.35
Wv2 = fWl ; l = v2
2g fg

46. SSD Equation SSD,m = 0.278V t + _____V2_____ 254f SSD in meter
V = speed in kmph
T = perception/reaction time (in seconds)
f = design coefficient of friction 46

47. STOPPING SIGHT DISTANCE FOR ASCENDING GRADIENT AND DESCENDING GRADIENT
SSD = 0.278vt v2
2g(f+ (n/100))
(or)
SSD = 0.278Vt V2
254(f - n/100)

48. Passing Distance Applied to rural two-lane roads
The distance required for a vehicle to safely overtake another vehicle on a two lane, two-way roadway and return to the original lane without interference with opposing vehicles
Designers assume single vehicle passing
Several assumptions are considered (vehicle being passed s traveling at a uniform speed, and others)
Normally use car passing car
Passing distance increased by type of vehicle
Minimum passing distance currently used are conservative

50. Geometric Design of Highways
Highway Alignment is a three-dimensional problem
Design & Construction would be difficult in 3-D so highway alignment is split into two 2-D problems

51. Horizontal Alignment Components of the horizontal alignment.
Properties of a simple circular curve.

52. Horizontal Alignment
Tangents
Curves

53. Tangents & Curves Tangent Curve Tangent to Circular Curve Tangent to
Spiral Curve to
Circular Curve

54. TWO CURVES
HORIZONTAL CURVES
VERTICAL CURVES

55. Stationing Horizontal Alignment Vertical Alignment
Therefore, roads will almost always be a bit longer than their stationing because of the vertical alignment
Draw in stationing on each of these curves and explain it

56. Alignment Design Definition of alignment:
Definitions from a dictionary
In a highway design manual: a series of straight lines called tangents connected by circular curves or transition or spiral curves in modern practice
Definition of alignment design: also geometric design, the configuration of horizontal, vertical and cross-sectional elements (first treated separately and finally coordinated to form a continuous whole facility)
Horizontal alignment design
Components of horizontal alignment
Tangents (segments of straight lines)
Circular/simple curves
Spiral or transition curves

57. Alignment Design Horizontal curves Simple curves
This consists of a single arc of uniform radius connecting two tangents
Compound curves
A compound curve is formed by joining a series of two or more simple curves of different radius which turn in same direction..

58. Simple curve elements

59. Simple curve in full superelevation

60. Compound curve

61. Alignment Design Horizontal curves TRANSITION CURVE Reverse curves
A curve having its radius varying gradually from a radius equal to infinity to a finite value equal to that of a circular curve
Reverse curves
A circular curve consistings of two simple curves of same or different radii and turn in the opposite direction is called reverse curve
Saturday, March 25, 2017

62. Reverse curves

63. VERTICAL ALIGNMENT
The vertical alignment of a transportation facility consists of
tangent grades (straight line in the vertical plane)
vertical curves. Vertical alignment is documented by the profile.

64. Vertical Alignment

65. Vertical curves

66. Convex and concave curves

67. Vertical Alignment Objective: Primary challenge
Determine elevation to ensure
Proper drainage
Acceptable level of safety
Primary challenge
Transition between two grades
Vertical curves
Sag Vertical Curve G1 G2 G1 G2
Crest Vertical Curve

68. Coordination of vertical and horizontal alignments

70. Outline Concepts Vertical Alignment Horizontal Alignment
Fundamentals
Crest Vertical Curves
Sag Vertical Curves
Examples
Horizontal Alignment
Superelevation
Other Non-Testable Stuff

71. Concepts Alignment is a 3D problem broken down into two 2D problems
Horizontal Alignment (plan view)
Vertical Alignment (profile view)
Stationing
Along horizontal alignment
12+00 = 1,200 ft.
Piilani Highway on Maui

72. Stationing Horizontal Alignment Vertical Alignment
Therefore, roads will almost always be a bit longer than their stationing because of the vertical alignment
Draw in stationing on each of these curves and explain it

73. From Perteet Engineering
Typical set of road plans – one page only
From Perteet Engineering

74. Vertical Alignment

75. Vertical Alignment Objective: Primary challenge
Determine elevation to ensure
Proper drainage
Acceptable level of safety
Primary challenge
Transition between two grades
Vertical curves
Sag Vertical Curve G1 G2 G1 G2
Crest Vertical Curve

76. Vertical Curve Fundamentals
Parabolic function
Constant rate of change of slope
Implies equal curve tangents
y is the roadway elevation x stations (or feet) from the beginning of the curve

77. Vertical Curve Fundamentals
PVI G1 δ
PVC G2
PVT
L/2 L x
Choose Either:
G1, G2 in decimal form, L in feet
G1, G2 in percent, L in stations

78. Relationships Choose Either: G1, G2 in decimal form, L in feet
G1, G2 in percent, L in stations
Relationships

79. Example
A 400 ft. equal tangent crest vertical curve has a PVC station of at 59 ft. elevation. The initial grade is 2.0 percent and the final grade is -4.5 percent. Determine the elevation and stationing of PVI, PVT, and the high point of the curve.
PVI
PVT
G1=2.0%
G2= - 4.5%
PVC: STA
EL 59 ft.

80. PVI G1=2.0% PVT G2= -4.5% PVC: STA 100+00 EL 59 ft.
400 ft. vertical curve, therefore:
PVI is at STA and PVT is at STA
Elevation of the PVI is 59’ (200) = 63 ft.
Elevation of the PVT is 63’ – 0.045(200) = 54 ft.
High point elevation requires figuring out the equation for a vertical curve
At x = 0, y = c => c=59 ft.
At x = 0, dY/dx = b = G1 = +2.0%
a = (G2 – G1)/2L = (-4.5 – 2)/(2(4)) =
y = x2 + 2x + 59
High point is where dy/dx = 0
dy/dx = x + 2 = 0
x = 1.23 stations
Find elevation at x = 1.23 stations
y = (1.23)2 + 2(1.23) + 59
y = ft

81. Other Properties G1, G2 in percent L in feet G1 x PVT PVC Y Ym G2 PVIYf
Last slide we found x = 1.23 stations

82. Other Properties K-Value (defines vertical curvature)
The number of horizontal feet needed for a 1% change in slope
G is in percent, x is in feet
G is in decimal, x is in stations

83. Crest Vertical Curves For SSD < L For SSD > L SSD h2 h1 L
PVI
Line of Sight
PVC G1
PVT G2 h2 h1 L
For SSD < L
For SSD > L

84. Crest Vertical Curves Assumptions for design Simplified Equations
h1 = driver’s eye height = 3.5 ft.
h2 = tail light height = 2.0 ft.
Simplified Equations
Minimum lengths are about 100 to 300 ft.
Another way to get min length is 3 x (design speed in mph)
For SSD < L
For SSD > L

85. Crest Vertical Curves
Assuming L > SSD…

86. Design Controls for Crest Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

87. Design Controls for Crest Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

88. Light Beam Distance (SSD)
Sag Vertical Curves
Light Beam Distance (SSD) G1
headlight beam (diverging from LOS by β degrees) G2
PVC
PVT h1
PVI
h2=0 L
For SSD < L
For SSD > L

89. Sag Vertical Curves Assumptions for design Simplified Equations
h1 = headlight height = 2.0 ft.
β = 1 degree
Simplified Equations
What can you do if you need a shorter sag vertical curve than calculated? Provide fixed-source street lighting
Minimum lengths are about 100 to 300 ft.
Another way to get min length is 3 x design speed in mph
For SSD < L
For SSD > L

90. Sag Vertical Curves
Assuming L > SSD…

91. Design Controls for Sag Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

92. Design Controls for Sag Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001

93. Example 1
A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long sag vertical curve. The entering grade is -2.4 percent and the exiting grade is 4.0 percent. A tree has fallen across the road at approximately the PVT. Assuming the driver cannot see the tree until it is lit by her headlights, is it reasonable to expect the driver to be able to stop before hitting the tree?
Assume that S>L (it usually is not but for example we’ll do it this way), therefore S = ft. which is less than L
Must use S<L equation, it’s a quadratic with roots of ft and ft.
The driver will see the tree when it is feet in front of her.
Available SSD is ft.
Required SSD = (1.47 x 30)2/2(32.2)( ) + 2.5(1.47 x 30) = ft.
Therefore, she’s not going to stop in time. OR
L/A = K = 150/6.4 = 23.43, which is less than the required K of 37 for a 30 mph design speed
Stopping sight distance on level ground at 30 mph is approximately 200 ft.

94. Example 2 Similar to Example 1 but for a crest curve.
A car is traveling at 30 mph in the country at night on a wet road through a 150 ft. long crest vertical curve. The entering grade is 3.0 percent and the exiting grade is -3.4 percent. A tree has fallen across the road at approximately the PVT. Is it reasonable to expect the driver to be able to stop before hitting the tree?
Assume that S>L (it usually is), therefore SSD = ft. which is greater than L
The driver will see the tree when it is feet in front of her.
Available SSD = ft.
Required SSD = (1.47 x 30)2/2(32.2)( ) + 2.5(1.47 x 30) = ft.
Therefore, she will be able to stop in time. OR
L/A = K = 150/6.4 = 23.43, which is greater than the required K of 19 for a 30 mph design speed on a crest vertical curve
Stopping sight distance on level ground at 30 mph is approximately 200 ft.

95. Example 3
A roadway is being designed using a 45 mph design speed. One section of the roadway must go up and over a small hill with an entering grade of 3.2 percent and an exiting grade of -2.0 percent. How long must the vertical curve be?
For 45 mph we get K=61, therefore L = KA = (61)(5.2) = ft.

96. Trinity Road between Sonoma and Napa valleys
Horizontal Alignment

97. Horizontal Alignment Objective: Primary challenge Fundamentals
Geometry of directional transition to ensure:
Safety
Comfort
Primary challenge
Transition between two directions
Horizontal curves
Fundamentals
Circular curves
Superelevation Δ

98. Horizontal Curve FundamentalsPI T Δ E M L PC
Δ/2 PT
D = degree of curvature (angle subtended by a 100’ arc) R R
Δ/2
Δ/2

99. Horizontal Curve FundamentalsPI T Δ E M L PC
Δ/2 PT R R
Δ/2
Δ/2

100. Example 4
A horizontal curve is designed with a 1500 ft. radius. The tangent length is 400 ft. and the PT station is What are the PI and PT stations?
Since we know R and T we can use T = Rtan(delta/2) to get delta = degrees
D = /R. Therefore D = 3.82
L = 100(delta)/D = 100(29.86)/3.82 = 781 ft.
PC = PT – PI = 2000 – 781 =
PI = PC +T = =
Note: cannot find PI by subtracting T from PT!

101. Superelevation Rv ≈ Fc α
Fcn
Fcp α e W
1 ft Wn Ff Wp Ff α

102. Superelevation Divide both sides by Wcos(α)
Assume fse is small and can be neglected – it is the normal component of centripetal acceleration

103. Selection of e and fs Practical limits on superelevation (e)
Climate
Constructability
Adjacent land use
Side friction factor (fs) variations
Vehicle speed
Pavement texture
Tire condition
The maximum side friction factor is the point at which the tires begin to skid
Design values of fs are chosen somewhat below this maximum value so there is a margin of safety

104. Side Friction Factor New Graph
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2004

105. New Table
Minimum Radius Tables

106. WSDOT Design Side Friction Factors
New Table
WSDOT Design Side Friction Factors
For Open Highways and Ramps
from the 2005 WSDOT Design Manual, M 22-01