chapter 2eded

8/10/2019 Chapter 2eded

1/24


2/24

!"

#

$!

$

"

Size Weight & axle

configuration

Power-to-weight

ratio

Turning radius

Turning path

Vehicle pollution

Design vehicle

Surface conditions Slopes

Curves


3/24

Size

Weight & axle configuration

Power-to-weight ratio

Turning radius

Turning path

Vehicle pollution

Design vehicle


4/24

Size

The size of vehicle (Length,height & width) need to be in

design limits Length and width of vehicles are important for designing on

street or off street parking facilities.

The height of vehicles are important for placing signs,designing underpass and overpasses.

Weight

Weight 0f vehicle( especially heavy vehicles) play important

role in design of flexible & rigid pavements


5/24

Axle configuration

As weight of vehicle is transferred to pavement

through axle and wheel their configuration has

important role

Number of axles (not Vehicles) of standard weightis considered as a variable in the pavement design.


6/24

Power-to-weight ratio

It is a parameter which characterizes the ease with which the

vehicle moves Cycles or Rickshaws have very low power-to-weight ratio and

their operating characteristics (acceleration capability,

sustainable speeds on slopes, etc.) are very poor. Automobiles, motor bikes etc. have high power-to-weight

ratios and hence good operating characteristics.

Heavy vehicles have poor power-to-weight ratios owing to theheavy weight of the vehicles.


7/24

Turning radius

The minimum radius of circular path traced by front

wheels of vehicle when the steering is turned to its

maximum extent.

It is dependent on the design and class of thevehicles.

Bus has larger turning radius than that of smaller

vehicles.


8/24


9/24

Turning path

Another important feature

As the rear wheels are fixed they follows different path

from that of front ones and hence the path of vehicle

movement is combine effect of both and i.e., turning

path.

Effective width of a vehicle on a turn increases.


10/24

Vehicle pollution

It represents the amount of pollutants released into

atmosphere by various vehicles which need to be

limited as per environmental recommendations

Vehicles releases

" % " & # ' %

! "" ! ()

(# $ $ )

# $% $ &!" (

)

" # "


11/24

Design vehicle

Various types of vehicles will be moving on a pavement

which have distinct properties;

An engineer should design a vehicle which will summarize

the combined effect of all vehicle the design for which

completes the need of all the vehicles

Vehicle classes includes:

i)Motorized two- wheeler, ii) Motorized three wheelers,iii)Pasenger cars or automobiles, iv) Buses , v) Single unit

trucks, vi)Semi trailers vii)Truck trailer combination,

viii)Slow non motorized vehicles


12/24

!"

#

$!

$

"


13/24

* (! # + $" #( # $! " )

, "+ ,&+ , &+ ,&!,&! $ ) " " * -).)

# $ * "+ (+ + $$ " $

/# # "" "+ %" # %"+

+ + # 0# $ )

The major role neglecting which cause loss of life and money.Extra factor and importance need to be considered in every

design


14/24

Comfort

Uncomfortable journey makes driver too loose interest on

driving leading to accidents, delay, vehicle efficiency, etc

Causes of discomfort to drivers are

1) Excessive deceleration rates: maximum value of

comfortable deceleration is 3 m/s2 .

2) Excessive jerk: limited to 0.7 m/s3

3) Glare: it is defined as an intense blinding light. Mostly

it occurs from headlights of oncoming vehicles.


15/24

Vision

Proper lightening and sight distance need to be provided

according to design speed & reaction time to avoidaccidents specially at crossings & intersections.

The important aspects are:1. Visual acuity:refers to how well a person can see. A person with

normal vision is having 6/6 vision.

2. Field of Vision: information on field of vision is important for

placement of road signs

3. Colour perception: based on discernibility considerations and

consideration of classification of signs codes in various countries

specify the color combination for various types of sign.


16/24

Design driver

Various driver have individual habits and hence the designershould provide comfort to maximum drivers

A driver who has the characteristics chosen by the designeris referred to as design driver.

For a design driver

1. Perception-reaction time:2.5 seconds

2. Comfortable deceleration rate: 3m/s2

3. Allowable jerk : about 0.7 m/s3

4. Visual acuity: 6/7.5


17/24

Surface conditions

Slopes

Curves

Control Mechanisms

Terminal facilities


18/24

Surface conditions

The surface friction, drainage conditions,

permeability water retention characteristics ,potholes etc play major role during rainfall ,etc.

Road surface should provide sufficient friction to

enable vehicles to move and stop effectively.

A very smooth road surface causes hindrance toflow of traffic.

Co-efficient of rolling friction offered by dry pavedsurface should be 0.5 and for wet surface it reducedto 0.3 .


19/24

Slopes

Attention must be paid to the slope and length of the

uphill section at the time of designing road.

Extra slope during curves, drainage slopes, etc. need

to be provided perfectly to avoid slipping orskidding of vehicle.

Braking distance:Another important matter relatedto slopes and friction of roads is braking distance

requirement of vehicle.


20/24

The figure given below shows a vehicle moving at a

speed of vim/s on a road inclined at an angle with

the horizontal.

The rolling friction co-efficient of the road surface

isfr..The vehicle will have to travel the minimum

distancexalong the inclined to reduce its speed

from vi to vf.


21/24

"# - " $ " (*"


22/24

" (!

)(tancos2

22

r

fi

fg

vv

+

=

#! (*" "

') $ (*"

$ $

)(2cos

22

r

fi

bfGg

vvxd

+

==


23/24

! ( ( %* $

%1 ")

#'

# 0# $

2))34,


24/24

Curves

Roads often have curves either in the horizontal plane

(when road turns) or in the vertical plane (when roadhas varying gradients.

Curves always pose a restriction on the distance over

which the driver can see the road. This factor is taken into account in the design of curves.

Horizontal curves usually create considerablecentrifugal force on the vehicles moving along them. Italso should be taken into account for design.

Banking, extra widening, field of vision, etc need to betaken care while designing curves

chapter 2eded

Documents