it deals with visible elements of a highway. it is influenced by: nature of terrain. type...
TRANSCRIPT
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).
TERRAIN CLASSIFICATION
Terrain type Percentage cross slope
of the country
Plain 0-10
Rolling 10-25
Mountainous 25-60
Steep >60
• Maximize the comfort
• Safety,
• Economy of facilities
• Sustainable Transportation Planning.
• geometric cross section
• vertical alignment
• horizontal alignment
• super elevation
• intersections
• various design details.
HIGHWAY GEOMETRIC DESIGN
• Cross sectional elements
• Sight distance
• Horizontal curves
• Vertical curves
Comparision of Urban and Rural Roads
Section Capacity
Peak Hour flow
Traffic fluctuations
Design Based on ADT
Speed
Urban Road Classification
• ARTERIAL ROADS• SUB ARTERIAL• COLLECTOR• LOCAL STREET• CUL-DE-SAC• PATHWAY • DRIVEWAY
Urban Road Classification
• ARTERIAL ROADS
• SUB ARTERIAL• COLECTOR• LOCAL STREET• CUL-DE-SAC• PATHWAY • DRIVEWAY
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
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
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
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)
CUL–DE- SAC
• Dead End Street with only one entry access for entry and exit.
• Recommended in Residential areas
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)
• 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.
Two-lane highway cross section, with ditches.
Two-lane highway cross section, curbed.
Two-lane highway cross section, curbed.
Divided highway cross section, depressed median, with ditches.
• 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.
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
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 2400 2.5
4800 3200 3.0
6000 4000 4.0
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.
MedianWidth 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
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
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.
CAMBER (OR) CROSS FALL
S. NoType 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 %
Types of Camber
• Parabolic or Elliptic
• Straight Line
• Straight and Parabolic
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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.
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
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Sight Distances
1. Stopping Sight distance
2. Over Taking Sight distance
3. Passing
4. Intermediate
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Sight Distance in Design• Stopping Sight Distance (SSD) – object in
roadway
• Passing Sight Distance (PSD) – pass slow vehicle
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
TOTAL REACTION TIME
• PERCEPTION TIME
• BRAKE REACTION TIME
TOTAL REACTION TIME DEPENDS ONPIEV THEORY
• PERCEPTION
• INTELLECTION
• EMOTION
• VOLIATION
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Perception-Reaction Process
• Perception
• Identification
• Emotion
• Reaction (volition)
PIEVUsed for Signal Design and Braking Distance
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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
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Typical Perception-Reactiontime range
0.5 to 7 seconds
Affected by a number of factors.
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Perception-Reaction Time Factors
• Environment• Urban vs. Rural• Night vs. Day• Wet vs. Dry
• Age
• Physical Condition• Fatigue• Drugs/Alcohol
• Distractions
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Age• Older drivers
– May perceive something as a hazard but not act quickly enough
– More difficulty seeing, hearing, reacting
– Drive slower– Less flexible
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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”
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Alcohol
• Affects each person differently
• Slows reaction time
• Increases risk taking
• Dulls judgment
• Slows decision-making
• Presents peripheral vision difficulties
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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
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
Braking DistanceKinetic Energy at the design speed of v m/sec= ½ m v2
= W v2 ; m = W/g 2g
W = weight of the VehicleG = acceleration due to gravity (9.9 m/sec2)Work done in stopping the vehicle = F x lF = Frictional forceL = braking distanceF = coeff of friction = 0.35
Wv2 = fWl ; l = v2
2g 2fg
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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
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)
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
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
Horizontal Alignment
• Components of the horizontal alignment.
• Properties of a simple circular curve.
Horizontal Alignment
Tangents Curves
Tangents & Curves
Tangent
Curve
Tangent to Circular Curve
Tangent to Spiral Curve toCircular Curve
TWO CURVES
• HORIZONTAL CURVES
• VERTICAL CURVES
Stationing
Horizontal Alignment
Vertical Alignment
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
1. 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 design1. Components of horizontal alignment
Tangents (segments of straight lines)Circular/simple curvesSpiral or transition curves
Alignment Design2. 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..
Simple curve elements
Simple curve in full superelevation
Compound curve
Alignment Design2. Horizontal curves
TRANSITION CURVEA curve having its radius varying gradually from a
radius equal to infinity to a finite value equal to that of a circular curve
Reverse curvesA circular curve consistings of two simple curves
of same or different radii and turn in the opposite direction is called reverse curve
61 Monday, April 10, 2023
Reverse curves
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.
Vertical Alignment
Vertical curves
Convex and concave curves
Vertical Alignment
• Objective: – Determine elevation to ensure
• Proper drainage• Acceptable level of safety
• Primary challenge– Transition between two grades– Vertical curves
G1 G2G1
G2
Crest Vertical Curve
Sag Vertical Curve
Coordination of vertical and horizontal alignments
Outline
1. Concepts2. Vertical Alignment
a. Fundamentalsb. Crest Vertical Curvesc. Sag Vertical Curvesd. Examples
3. Horizontal Alignmenta. Fundamentalsb. Superelevation
4. Other Non-Testable Stuff
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
Stationing
Horizontal Alignment
Vertical Alignment
From Perteet Engineering
Vertical Alignment
Vertical Alignment
• Objective: – Determine elevation to ensure
• Proper drainage• Acceptable level of safety
• Primary challenge– Transition between two grades– Vertical curves
G1 G2G1
G2
Crest Vertical Curve
Sag Vertical Curve
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
cbxaxy 2
Vertical Curve Fundamentals
G1
G2
PVI
PVT
PVC
L
L/2
δ
cbxaxy 2
x
Choose Either:• G1, G2 in decimal form, L in feet• G1, G2 in percent, L in stations
RelationshipsChoose Either:• G1, G2 in decimal form, L in feet• G1, G2 in percent, L in stations
G1
G2
PVI
PVT
PVC
L
L/2
δ
x
1 and 0 :PVC At the Gbdx
dYx
cYx and 0 :PVC At the
L
GGa
L
GGa
dx
Yd
22 :Anywhere 1212
2
2
Example
A 400 ft. equal tangent crest vertical curve has a PVC station of 100+00 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.
G1=2.0%
G2= - 4.5%
PVI
PVT
PVC: STA 100+00EL 59 ft.
G1=2.0%
G2= -4.5%
PVI
PVT
PVC: STA 100+00EL 59 ft.
Other Properties
G1
G2
PVI
PVTPVC
x
Ym
Yf
Y
2
200x
L
AY
800
ALYm
200
ALY f
21 GGA
•G1, G2 in percent•L in feet
Other Properties
• K-Value (defines vertical curvature)– The number of horizontal feet needed for a
1% change in slope
A
LK
1./ GKxptlowhigh
Crest Vertical Curves
G1G2
PVI
PVTPVC
h2h1
L
SSD
221
2
22100 hh
SSDAL
A
hhSSDL
2
212002
For SSD < L For SSD > L
Line of Sight
Crest Vertical Curves
• Assumptions for design– h1 = driver’s eye height = 3.5 ft.
– h2 = tail light height = 2.0 ft.
• Simplified Equations
2158
2SSDAL
ASSDL
21582
For SSD < L For SSD > L
Crest Vertical Curves
• Assuming L > SSD…
2158
2SSDK
Design Controls for Crest Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001
Design Controls for Crest Vertical Curves
fro
m A
AS
HT
O’s
A P
olic
y o
n G
eo
me
tric
De
sig
n o
f H
igh
wa
ys a
nd
Str
ee
ts 2
00
1
Sag Vertical Curves
G1 G2
PVI
PVTPVC
h2=0h1
L
Light Beam Distance (SSD)
tan200 1
2
Sh
SSDAL
A
SSDhSSDL
tan2002 1
For SSD < L For SSD > L
headlight beam (diverging from LOS by β degrees)
Sag Vertical Curves
• Assumptions for design– h1 = headlight height = 2.0 ft.
– β = 1 degree
• Simplified Equations
SSD
SSDAL
5.3400
2
A
SSDSSDL
5.34002
For SSD < L For SSD > L
Sag Vertical Curves
• Assuming L > SSD…
SSD
SSDK
5.3400
2
Design Controls for Sag Vertical Curves
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2001
Design Controls for Sag Vertical Curves
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AS
HT
O’s
A P
olic
y o
n G
eo
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tric
De
sig
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f H
igh
wa
ys a
nd
Str
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ts 2
00
1
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?
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?
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?
Horizontal Alignment
Horizontal Alignment
• Objective: – Geometry of directional transition to ensure:
• Safety• Comfort
• Primary challenge– Transition between two directions– Horizontal curves
• Fundamentals– Circular curves– Superelevation
Δ
Horizontal Curve Fundamentals
R
T
PC PT
PI
M
E
R
Δ
Δ/2Δ/2
Δ/2
RRD
000,18
180100
2tan
RT
DRL
100
180
L
Horizontal Curve Fundamentals
1
2cos
1RE
2
cos1RM
R
T
PC PT
PI
M
E
R
Δ
Δ/2Δ/2
Δ/2L
Example 4
A horizontal curve is designed with a 1500 ft. radius. The tangent length is 400 ft. and the PT station is 20+00. What are the PI and PT stations?
Superelevation cpfp FFW
cossincossin22
vvs gR
WV
gR
WVWfW
α
α
Fcp
Fcn
Wp
Wn F f
F f
α
Fc
W 1 fte
≈Rv
Superelevation
cossincossin22
vvs gR
WV
gR
WVWfW
tan1tan2
sv
s fgR
Vf
efgR
Vfe s
vs 1
2
efg
VR
sv
2
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
Side Friction Factor
from AASHTO’s A Policy on Geometric Design of Highways and Streets 2004
New Graph
Minimum Radius TablesNew Table
WSDOT Design Side Friction Factors
from
the
200
5 W
SD
OT
Des
ign
Man
ual,
M 2
2-01
New Table
For Open Highways and Ramps