Introduction to transportation engineering

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Transportation Engineering
(CE-421)

What is Transportation Engineering….?
 Transport is the movement of humans, animals and
goods from one place to another.
 It is the application of technology and scientific
principles to the planning, functional design, operation
and management of facilities for any mode of
transportation in order to provide safe, efficient,
convenient movement in an economic and
environmentally sustainable way.
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• J. H. Banks (1998), An Introduction to Transportation Engineering,
McGraw Hill International

Functional Classification Of Transportation Engineering
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Functional Classification Of Transportation Engineering
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Mode of Transportation
 Land (Through Roads and Railway Line)
 Water (Through Sea and Rivers)
 Air (Through airplanes)
 Pipe Line (Water, Oil and other fluids)
 Cable (Chairlifts, Cable-cars, Ski lift)
 Space (Space Shuttles, Space rockets)
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Highway Engineering
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Highway engineering is an engineering discipline
branching from civil engineering that involves the
planning, design, construction, operation, and maintenance
of roads, bridges, and tunnels to ensure safe and
effective transportation of people and goods.
Highway engineering became prominent towards the latter half of the
20th Century after World War II. Standards of
highway engineering are continuously being improved.
Highway engineers must take into account future traffic flows, design
of highway intersections/interchanges, geometric alignment and
design, highway pavement materials and design, structural design of
pavement thickness, and pavement maintenance.

Classification Of Roads
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Road , Street & Highway.....?
Avenue?
Boulevard?
Arcade?
Alley?
Cul-De-Sac…?
Pedestrian….?
Passenger Car…?
SU Truck…..? SU: Single Unit

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Elements of Typical Road
X-Sections

Road Cross Section elements are those
features of a roadway which form its effective
width.
Typical Cross-Section Elements of Roads
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 The cross-section of a highway includes a number of elements
critical to the design of the facility. The cross-section includes the
following features:
 Right of Way
 Travel lanes
 Shoulders
 Side slopes
 Curbs
 Medians and median barriers
 Guardrails
 Drainage channels
 Camber
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 General design practice is to specify the cross-section at each
station (i.e., at points 100 ft. or 20m apart and at intermediate
points where a change in the cross-sectional design occurs)
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 Cross section— A vertical section of the ground and roadway at right
angles to the centerline of the roadway, including all elements of a
highway or street from right-of-way line to right-of-way line
 Roadway—The portion of a highway, including shoulders, for
vehicular use. A divided highway has two or more roadways
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 Traveled way / Carriage Way —The portion of the roadway for the
movement of vehicles, exclusive of shoulders and bicycle lanes.
 In ‘single carriageway’ traffic runs in both direction without
separation of road. Also known as ‘two way highway’.
 A dual carriageway or divided highway is a road in which the two
directions of traffic are separated by a central barrier or strip of land,
known as a central reservation or median. It can accommodate more
traffic in a duration (capacity) as compared to single carriage way.
Also known as ‘one way highway’.
‘Travelled way width depends on the ,
• No. of lanes
• Type of road
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 Purpose of lane width is to accommodate vehicle (Design Vehicle
generally taken as 8’ wide) width however,
 The lane width of a roadway greatly influences the safety and
comfort of driving. Lane widths of 2.7 to 3.6 m [9 to 12 ft] are
generally used, with a 3.6-m [12-ft] lane predominant on most high-
type highways.
 Lane widths also affect highway level of service. Narrow lanes force
drivers to operate their vehicles closer to each other laterally than
they would normally desire. Restricted clearances have much the
same effect. In a capacity sense the effective width of traveled way is
reduced when adjacent obstructions such as retaining walls and
parked cars restrict the lateral clearance.
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 Right of Way— Right of way is the width of land strip
acquired/reserved for the development of road facility in the public
interest.
 Right of Way width should be adequate to accommodate the
elements that makeup the road cross section and for the future
development purposes. For example: roadway, drainage, side slopes
etc.
 Right of way width depends on Factors,
• Class of highway
• Traffic flow quantity
• Traffic Growth
 Control Line is the line representing the nearest limits of future
uncontrolled building activity in relation to road.

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 Camber is convexity of road ‘also known as cross slope’ is provided
to facilitate drainage of the pavement laterally.
It may be crowned ‘with the highest point in the center and sloping
downward towards both side.
Or
Uni-directional’ cross slope on entire the cross section of
pavement.
Amount of cross slope depends on,
I. Smoothness of the pavement surface
II. Intensity of rainfall in the area
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o Undivided traveled ways (two- and
multilane) on tangents and flat curves
have a crown in the middle and slope
downward toward both edges
o The downward cross slope may be a
plane or rounded section (parabolic),
or a combination of the two
o With plane cross slopes, there is a
cross slope break at the crown line and
a uniform slope on each side
o Rounded cross sections usually are
parabolic, with a slightly rounded
surface at the crown line and
increasing cross slope toward the edge
of the traveled way
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• Cross slopes steeper than 2% on paved, high-speed roads (central crown
line) - not desirable as in passing maneuvers, drivers cross and re-cross the
crown line and negotiate a total cross slope change of over 4 percent –
difficult to maintain position
• Change in the cross slope of 3-4% causes swaying of high body vehicles -
Rounded crowns reduce discomfort
• Intense rainfall Areas:
– cross slope on paved surfaces upto 2.5%
– three or more lanes one direction – max cross slope 4%
• On low-type pavements (penetration surfaces, compacted earth, etc.), the
range of drainage cross slope - 2% and 6%
• A steep lateral slope reduces water ponding and the width of the water
flow along the curb.
• A flat lateral slope reduces vehicles' drift towards the low edge
• Lateral drift of vehicles at high speed is barely perceptible on cross slopes
up to 2%
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• A shoulder is the portion of the roadway adjoining with the traveled
way that accommodates stopped vehicles, emergency use, and
lateral support of sub-base, base, and surface courses
• It varies in width from only 0.6 m [2 ft] on minor rural roads to
approximately 3.6 m [12 ft] on major roads where the entire
shoulder may be stabilized or paved
• “Graded Shoulder” - measured from the edge of the traveled way to
the intersection of the shoulder slope and the side-slope planes
• “Usable Shoulder” - the actual width that can be used when a driver
makes an emergency or parking stop. Where the side-slope is 1V:4H
or flatter, the “usable” width is the same as the “graded” width since
the usual rounding 1.2 to 1.8 m [4 to 6 ft] wide at the shoulder
break will not lessen its useful width appreciably
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Functions of shoulders:
• Accommodation of stopped vehicles (disabled vehicles)
• Emergency use
• Lateral support for the pavement
• Space for bicycles and pedestrians
• Driving comfort (freedom from strain)
• Improvement in sight distance
• Improvement in highway capacity
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Shoulder can be surfaced by using:
• Turf
• Gravel
• Crushed rock
• Bituminous treatment
• Asphalt or concrete pavements
Width of shoulders
• Low-type roads -- minimum 0.6 m [2 ft.], recommended 1.8-2.4 m
[6-8 ft.]
• Shoulder usable by bicycles -- minimum 1.2 m [4 ft.]
• High-type roads -- minimum 3.0 m, recommended 3.6 m [12 ft.]
Clearance to roadside elements (barriers, walls, signs, etc.)
• High-type roads -- 0.6 m [2 ft.] to the edge of the usable shoulder
• Low-type roads – Barrier may be placed at the outer edge of
shoulder (minimum 1.2 m [4 ft.] to the edge of the traveled way)
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Other rules
• Shoulders should be continuous
• Shoulders on bridges should have the same width as on the
approach sections
Cross slopes
• Bituminous and concrete shoulders -- 2-6 %
• Gravel and crushed rock shoulders -- 4-6 %
• Turf shoulder -- about 8 %
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Side Slopes
Side slopes of embankments and cut sections depend upon,
• Type of soil
• Depth of cutting or height of embankments
Flat slope of embankment provides safety for traffic and conducive
for erosion control but is costly.
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Side slope of cutting depends upon soil type. Following guide line
can be useful.
Ordinary Soil 2:1 to 1:1
Disintegrated rocks ½ :1 to ¼:1
Shale/Soft Rock ¼:1 to 1/8:1
Medium Rock 1/12:1 to 1/16:1
Hard Rock Near Vertical (in steps)

What is Median
• A median is the portion of a highway separating opposing directions
of the traveled way
• Median width is expressed as the dimension between the edges of
the traveled way for the roadways in the opposing directions of
travel, including the width of the right (inner) shoulders, if any
Function of medians
• Separate opposing traffic
• Recovery area for out-of-control vehicles
• Stopping area in case of emergency
• Storage of right-turning and U-turning vehicles
• Minimize headlight glare
• Provision for future lanes
• Median in an urban area - may offer an open green space, may
provide a refuge area for pedestrians crossing the street, 34

Types of medians
• depressed - on freeways with slope 1:6 (1:4), drainage inlets with
safety grates
• raised - relatively narrow on arterial streets, plantation planned
• flush - crowned or slightly depressed on all types of urban arterials
• convenient to convert into two-way right-turn lanes (3.0-4.8 m wide)
Visibility and Contrast
• For maximum efficiency, a median should be highly visible both night
and day
• should contrast with the traveled way
Width of Median
• Width of medians ranges from 1.2 to 24 m [4 to 80 ft.]
• Full separation of traveled ways is achieved when the median is at
least 12 m [40 ft.] wide
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Curb is a vertical or sloping member along the Pavement or shoulder
of a road.
Functions of curbs
• drainage control
• roadway edge delineation
• right-of-way reduction
• delineation of pedestrian walkways
Types of curbs:
Vertical curbs (Barrier Kerb) -- discourage vehicles from leaving
the roadway, not desirable on high-speed highways, desirable
on urban roads, and along long walls, tunnels to protect safety
walks
Sloping curbs (Mountable Kerb) -- vehicle can cross them readily
when required, used at median edges, to outline channelizing
islands, at the outer edge of the shoulder. 44

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Exhibit 4-6
Sloping Curbs
Vertical Curb
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• Drainage channels perform the vital function of collecting
and conveying surface water from the highway right-of-
way. Drainage channels should:
• have adequate capacity for the design runoff,
• minimize damage to the highway caused by unusual
storm water,
• minimize risk for motorists,
• be resistant to the high speed water flows where
expected,
• prevent sedimentation of the particles carried by
water
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Design considerations of highway drainage includes
• safety
• good appearance
• economy in maintenance
This can be achieved by applying
• flat sideslopes
• wide drainage channels
• rounding
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• Traffic barriers are used to prevent vehicles that leave the traveled
way from colliding with objects that have greater crash severity
potential than the barrier itself
• Because barriers are themselves a source of crash potential, their
use should be carefully considered
• AASHTO Roadside Design Guide provides detailed information
regarding traffic barriers
• Traffic barriers includes:
– longitudinal barriers -The primary function of longitudinal
barriers is to redirect errant vehicles
– crash cushions - The primary function of crash cushions is to
decelerate errant vehicles to a stop.
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Six alternatives of dealing with roadside hazard
• remove the obstacle
• relocate the obstacle
• use a breakaway device
• use barriers
• delineate the obstacle
• do nothing
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• Longitudinal barriers are located along the roadside and in medians
• A roadside barrier is a longitudinal system used to shield motorists
from obstacles or slopes located along either side of a roadway
• A median barrier is a longitudinal system used to minimize the
possibility of an errant vehicle crossing into the path of traffic
traveling in the opposite direction
• Longitudinal barriers have three types:
o Flexible - dynamic deflection upon impact, designed to contain
rather than redirect vehicles
o Semirigid - redirect vehicles along the path
o Rigid - does not deflect, by deformation of the vehicle sheet
metal
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• Barriers should be installed only if it is clear that they offer the least
crash and casualty potential.
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• Median Barriers: The following justifies the use of median barriers:
– multilane roadway,
– heavy traffic,
– narrow median,
– traveled ways at different elevations,
– rigid obstacles in the median,
– partial access control.
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Crash cushions are protective systems that prevent errant vehicles
from impacting roadside obstacles by:
o decelerating the vehicle to a safe stop when hit head-on
o redirecting vehicles away from the obstacle
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Lateral Clearance
It is the distance between the extreme edge of the carriage way to the
nearest obstruction.
Vertical Clearance
It is the height above the highest point of travelled way to the lowest
point of overhead structure.
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Vertical Clearance

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Introduction to transportation engineering

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