Geometric Design

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 gt60
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

9
(No Transcript)
10
(No Transcript)
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
CULDE- 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, 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 No of Persons/Hr Required Width of footpath (m)
All in one direction In both direction Required Width of footpath (m)
1200 800 1.5
2400 1600 2.0
3600 2400 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 gt 200 separate cycle track for
  cycle traafic of 100 is sufficient.

24
Median

• Width of Median Depends on
• 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 - 2.5 ( 1 in 50 to 1 in 40)
3 Bituminous Surfacing or Cement Concrete surfacing 1.7 - 2.0
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 DRIVERS 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 ONPIEV THEORY

• PERCEPTION
• INTELLECTION
• EMOTION
• VOLIATION

36
Perception-Reaction Process

• Perception
• Identification
• Emotion
• Reaction (volition)

PIEV Used for Signal Design and Braking Distance
36
37
Perception-Reaction Process

• Perception
• 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
38
Typical Perception-Reaction time range
0.5 to 7 seconds
Affected by a number of factors.
38
39
Perception-Reaction Time Factors

• Environment
• Urban vs. Rural
• Night vs. Day
• Wet vs. Dry
• Age
• Physical Condition
• Fatigue
• Drugs/Alcohol
• Distractions

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
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
42
Alcohol

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

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 1000 x t
• 60 x 60
• 0.278 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 2fg

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

49
(No Transcript)
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
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
• 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
• 61 Wednesday, December 04, 2013

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
• Determine elevation to ensure
• Proper drainage
• Acceptable level of safety
• Primary challenge
• Transition between two grades
• Vertical curves

Sag Vertical Curve
G1
G2
G2
G1
Crest Vertical Curve
68
Coordination of vertical and horizontal alignments
69
(No Transcript)
70
Outline

• Concepts
• Vertical Alignment
• Fundamentals
• Crest Vertical Curves
• Sag Vertical Curves
• Examples
• Horizontal Alignment
• Fundamentals
• 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
• 1200 1,200 ft.

Piilani Highway on Maui
72
Stationing
Horizontal Alignment
Vertical Alignment
73
From Perteet Engineering
74
Vertical Alignment
75
Vertical Alignment

• Objective
• Determine elevation to ensure
• Proper drainage
• Acceptable level of safety
• Primary challenge
• Transition between two grades
• Vertical curves

Sag Vertical Curve
G1
G2
G2
G1
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
d
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

79
Example
A 400 ft. equal tangent crest vertical curve has
a PVC station of 10000 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
G12.0
G2 - 4.5
PVC STA 10000 EL 59 ft.
80
PVI
PVT
G12.0
PVC STA 10000 EL 59 ft.
G2 -4.5
81
Other Properties

• G1, G2 in percent
• L in feet

G1
x
PVT
PVC
Y
Ym
G2
PVI
Yf
82
Other Properties

• K-Value (defines vertical curvature)
• The number of horizontal feet needed for a 1
  change in slope

83
Crest Vertical Curves
SSD
PVI
Line of Sight
PVC
G2
PVT
G1
h2
h1
L
For SSD lt L
For SSD gt L
84
Crest Vertical Curves

• Assumptions for design
• h1 drivers eye height 3.5 ft.
• h2 tail light height 2.0 ft.
• Simplified Equations

For SSD lt L
For SSD gt L
85
Crest Vertical Curves

• Assuming L gt SSD

86
Design Controls for Crest Vertical Curves
from AASHTOs A Policy on Geometric Design of
Highways and Streets 2001
87
Design Controls for Crest Vertical Curves
from AASHTOs A Policy on Geometric Design of
Highways and Streets 2001
88
Sag Vertical Curves
Light Beam Distance (SSD)
G1
headlight beam (diverging from LOS by ß degrees)
G2
PVT
PVC
h1
PVI
h20
L
For SSD lt L
For SSD gt L
89
Sag Vertical Curves

• Assumptions for design
• h1 headlight height 2.0 ft.
• ß 1 degree
• Simplified Equations

For SSD lt L
For SSD gt L
90
Sag Vertical Curves

• Assuming L gt SSD

91
Design Controls for Sag Vertical Curves
from AASHTOs A Policy on Geometric Design of
Highways and Streets 2001
92
Design Controls for Sag Vertical Curves
from AASHTOs 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?
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?
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?
96
Horizontal Alignment
97
Horizontal Alignment

• Objective
• Geometry of directional transition to ensure
• Safety
• Comfort
• Primary challenge
• Transition between two directions
• Horizontal curves
• Fundamentals
• Circular curves
• Superelevation

?
98
Horizontal Curve Fundamentals
PI
T
?
E
M
L
?/2
PT
PC
R
R
?/2
?/2
99
Horizontal Curve Fundamentals
PI
T
?
E
M
L
?/2
PT
PC
R
R
?/2
?/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 2000. What are the PI and PT
stations?
101
Superelevation

Rv
Fc
a
Fcn
Fcp
a
e
W
1 ft
Wn
Ff
Wp
Ff
a
102
Superelevation
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

104
Side Friction Factor
New Graph
from AASHTOs A Policy on Geometric Design of
Highways and Streets 2004
105
Minimum Radius Tables
New Table
106
WSDOT Design Side Friction Factors
New Table
For Open Highways and Ramps
from the 2005 WSDOT Design Manual, M 22-01