Transcript traffic volume.pptx

1



Carried out to analyse traffic characteristics.
Help in deciding geometric design features and traffic control.
Traffic surveys for collecting data are also called Traffic
Census.
Various traffic studies are:
 Traffic volume study
 Speed study
 Spot speed study
 Speed and delay study
 Origin and Destination (O&D) study
 Traffic flow characteristics
 Traffic capacity study
2
 Parking study
 Accident study
3

Traffic Volume :- Number of vehicles crossing a section of
road per unit time at any selected period.

One of the fundamental measures of traffic on a road
system.

Used as a quantity measure of flow.

Unit: vehicles per day and vehicles per hour.
4

Measure of relative importance of roads for deciding the priority for
improvement & expansion.

Used in planning , traffic operation and control of existing facilities
and to design new facilities.

Analysis of traffic patterns & trends

Classified volume -structural design of pavements & geometric design

For planning one way streets and other regulatory measures.

Turning movement study for design of intersection , signal timings
etc

5
Pedestrian traffic volume for planning of side walks, pedestrian
signals etc.

Methods for volume counts are
1.
Manual method
2.
Combination of manual and mechanical method
3.
Automatic devices
4.
Moving Observer Method
5.
Photographic method
6

Employs a field team to count and classify traffic volume.
Procedure

No. of observers required depends upon no. of Lanes and
type of information required.

More desirable to record traffic in each direction of travel
by posting separate observers for each direction.

For all-day counts ,work in three shifts of 8 hrs can be
arranged.

Data is recorded by Five- dash system. (IIII)
7

Details such as vehicle classification and no. of occupants can
be obtained.

Records Turning movement data of vehicles at intersections.

Analyzing traffic characteristics in unusual conditions such as
adverse weather conditions, traffic breakdowns, temporary
closure of any lane of highway etc.

Comparatively cheaper method of counting.

It is often necessary to check the accuracy of automatic devices

Data accumulated by manual methods are easy to analyze.
8

Not practicable to have manual count for 24 hrs of the day
and throughout the year.

Counts of remote areas is possible by automatic devices.
9
Multiple Pen Recorder

A chart moves continuously at the speed of a clock.
Different pens record different events. Actuation of pen is
by pressing the corresponding electric switch.

When a particular class of vehicle passes ,the associated
switch may be pressed and this operates the pen on the
channel. This represents the arrival of that particular
class of vehicle.
10
MULTIPLE PEN RECORDER
ADVANTAGES

Permanent record is kept about arrival of each class of
vehicle.

Classification
and
vehicle
count
are
performed
simultaneously.
11
1. Pneumatic Tube

Flexible tube with one end sealed is clamped to road at
right angles to pavement.

Other end connected to a diaphragm actuated switch.

When an axle of vehicle crosses the tube, a volume of air
gets displaced thus creating a pressure which closes the
electrical contact through switch.

Two such contact result in one count.
12
PNEUMATIC TUBE
Disadvantages
 When vehicles with more than two axles are
present.
 Tubes get damaged by crawler tractors, tyre chains
etc.
 Difficulty in fixing them to gravel surfaces.
13
2. Electric Contact Devices

A pair of steel strips are contained in a rubber pad which
is buried beneath the surface.

When vehicle passes over rubber pad ,steel strips come
into contact with each other and electric current flows.

Electric contact devices are installed in each lane.
14
3. Coaxial Cables.

A coaxial cable is clamped across the road surface,

signals are generated when vehicle passes over it.

Signals actuate the counter.

Advantage : lesser susceptibility to damage.
15
4. Photo-electric Device.
On one end of road , a source of light emits a beam across
the road.
 At the other end is a photo –cell which can distinguish
between the light beam and absence of light beam.
 Passage of vehicle in the path of light beam obstructs the
beam and detected by photo-cell.

Disadvantages
 Obstruction can be caused by pedestrians also.
 More than one vehicle positioned in the beam line
16
simultaneously can register as one vehicle.
5. Radar

Based on Doppler Effect.

Compares the frequency of a transmitted
radio
signal with the frequency of the reflected signal.

When a moving vehicle interrupts the signal , a
frequency difference exists.
17

Traffic Flow Maps:



using
bands
Intersection Flow Diagrams


Show volume along various routes by
proportional to traffic volume carried.
Thickness of lines represent traffic volume.
Give direction and volume of traffic through an intersection.
Trend charts


Shows the hourly , daily or monthly changes in volume
through an area.
Useful for planning future expansion, design and regulation. 18



Annual Average Daily Traffic(AADT)
 The total yearly volume divided by number of days in the year.
Average Daily Traffic(ADT)
 The total volume during a given time period, in whole days
greater than one day and less than one year, divided by number
of days in that time period.
Thirtieth highest hourly volume
 Hourly volume that will be exceeded only 29 times in a year
and all other hourly volumes of the year will be less than this
value.
 High facilities are designed for 30th highest hourly traffic
volume. Generally taken as the hourly volume for design.
19
 Cost will be less.
 There will be congestion only during 29 times in a year.
20

Spot Speed


Average Speed


Instantaneous speed of a vehicle at a specified
location.
Average of the spot speeds of all vehicles passing a
given point on the highway.
Running Speed

Average speed maintained by a vehicle over a given
course while the vehicle is in motion.

Running speed= Length of course / Running time
= Length of course /( Journey time- Delays)
21



Journey speed
 Also known as overall travel speed
 It is the effective speed between two points. It is the distance
between two points divided by the total time taken by the
vehicle to complete the journey ,including all delays.
 Journey speed = Distance/ Total journey Time (including
Delays).
Time Mean Speed
 Average of instantaneous speeds of observed vehicles at a spot
over a period of time.
Space Mean speed
 Average of the speed measurements at an instant of time over 22
a space.

Design of geometric features.

For regulation and control of traffic operations.

To establish safe speed limits.

Location and size of traffic signs.

For analyzing causes of accidents.

To study the traffic capacity, problems of congestion on
roads etc.

To decide speed trends.
23
The methods available for measuring spot speed can be
grouped as
 Those observations that require time taken by a vehicle to
cover a known distance.
It consist of
 long base methods- vehicles are timed over a long distance.
 Short base methods- vehicles are timed over a long distance,
say about 2m.

Radar Speedometer
instantaneous speed.
 Photographic method.

which
automatically
records
24
I). Those observations that require time taken by a vehicle to
cover a known distance.
 Long base methods
Direct timing Procedure
 Enoscope
 Pressure contact tubes.

a)Direct timing Procedure
Simplest method
Two reference points are marked on the pavement at a
suitable distance apart and an observer starts and stops
stopwatch as a vehicle crosses these two marks.
25

From known distance and time, speed can be calculated.

Disadvantage: errors due to parallax effect.

Observation by two observers one at each reference points

First observer standing at the point in which the vehicle pass
first, signals and seconds observer starts the stop watch. The
second observer stops the stop watch when he observes the same
vehicle passing the reference point.

Disadvantage: reaction time of two observers.
26
b). Enoscope

Also known as mirror box

L-shaped box, open at both ends ,with a mirror set
at 45 ˚ to the arms of the instrument.
27
vehicle
mirror
45˚
observer
It bends the line of sight of the observer perpendicular to the
path of vehicle.
28
29

The instrument is placed directly opposite to the first reference
point and the observer stations himself at the second reference
point.

Stop watch is started as soon as the vehicle passes the first point
and is stopped as soon as it passes the observer.

If two enoscope is used, the observer stations himself midway
between two reference points.

Advantages:
Eliminates parallax error.
 Equipment is of low cost, simple and can set up easily

30
Pneumatic tubes are used.
 At both reference points, a flexible rubber tube is fastened to
the pavement in perpendicular direction to the path of
vehicle travel.
 A vehicle crossing the tube compresses the air in it
,actuating an air impulse switch.
 When
the air impulse is sent, it activates
an
electromagnetically controlled stopwatch in the hands of
observer.
 When
vehicle passes over second tube, stopwatch
automatically stops.
 Reading is noted by observer.
31



Advantage

Low initial cost

Simple to install

Easily maintained
Disadvantage

Tubes are easily seen by drivers and may affect their
behavior.
32
Works on the Doppler principle.
 Speed of a moving body is proportional to change in
frequency between the Radio wave transmitted to the
moving body and the radio wave received back.

Instrument directly measures speed.
 Instrument is setup near the edge of carriageway at a
height of 1m.

The speed meter is so kept that the angle between
direction of travel of vehicle and axis of transmission of
33
radio wave is as low as possible, say within 20˚.
 Speed of vehicles in both directions can be observed.


Time-lapse camera photography can be used.

Photographs are taken at fixed intervals of time(say one
second per frame) on a special camera.

By projecting the film on a screen, the passage of any
vehicle can be traced with reference to time.

Images by video cameras can be also used.
34

Average speed of vehicles

From spot speed data, distribution tables are prepared by
arranging the data in groups covering various speed ranges
and number of vehicles in each range.


Arithmetic mean is the average speed.
Cumulative speed of vehicles

Graph is plotted with average values of each group on Xaxis and cumulative % of vehicles travelling at different
35
speeds.

85th percentile speed: Speed
at or below 85 % of
vehicles are passing the point of highway.

Only 15 % of vehicles exceed the speed at that spot.

Drivers exceeding 85th percentile speed are considered to
drive faster than the safe speed. Hence 85th percentile
speed is adopted for Safe speed limit at that zone.

50th percentile speed: median speed.

98th percentile speed: used for geometric design.

15th percentile speed: represents the lower speed limit.
36

Modal average

A frequency distribution curve of spot speeds is plotted
with speed of vehicles or average values of each group on
the Y-axis. This graph is called Speed Distribution Curve.

The peak value of the curve is denoted as Modal Speed.

Modal speed: speed at which the greatest proportion of
vehicles move.
37