Upload
kwasi-agyeman-boakye
View
222
Download
1
Embed Size (px)
Citation preview
7/28/2019 3A Traffic Studies
1/38
KAAF UNIVERSITY COLLEGE
Civil Engineering DepartmentCollege of Engineering
__________________________________
Transportation Engineering ICIV 367
Lecture 3A_ Traffic Studies
Kwasi Agyeman Boakye ( [email protected])
1
7/28/2019 3A Traffic Studies
2/38
KAAF UNIVERSITY COLLEGE
Introduction
Traffic Studies is important to;
Managing the physical system, Investigating trends over time, Understanding the
needs and choices of the public and industry, Calibrating basic relationships or
parameters, Assessing the effectiveness of improvements, Assessing potential
impacts, Evaluating facility or system performance
It can be categorized under;
Inventories; Providing a list or graphical display of existing information, such as
street widths, parking spaces, transit routes, traffic regulation etc
Dynamic Studies; Involve the collection of data under operational conditions and
include studies of speed, traffic volume, travel time and delay, parking and crashes.Administrative Studies; Involve studies using existing engineering records,
available in government agencies and departments.
Examples;Volume studies, Speed studies, Travel Time studies, Delay studies,
Density Studies, Accident Studies, Parking Studies, Goods Movement and TransitStudies, Pedestrian Studies etc. 2
7/28/2019 3A Traffic Studies
3/38
7/28/2019 3A Traffic Studies
4/38
KAAF UNIVERSITY COLLEGE
Speed StudiesPurpose
Speed studies may be used for;
Establish parameters for traffic operation and control, such as speed zones, speed limits and
passing restrictions.
Evaluate the effectiveness of traffic control devices, such as a variable message signs at work
zones.
Monitor the effect of speed enforcement programmes such as the use of radar guns.
Evaluate and determine the adequacy of highway geometric characteristics such as radii of
horizontal curves and lengths of vertical curves.
Evaluate the effect of speed on highway safety through the analysis of crash data for different
speed characteristics.
Determine speed trends
Determine whether complaints about speeding are valid 4
7/28/2019 3A Traffic Studies
5/38
KAAF UNIVERSITY COLLEGE
Manual Method of Measuring
Spot Speed
The main manual method used is the Direct timing procedure .
Direct Timing Procedure
Two reference points are marked on the pavement at a suitable distance apart andan observer starts and stops an accurate stop watch as a vehicle crosses these two
marks. From the known distance and the measured time intervals speeds are
calculated.
Skilled observers can read a stop watch to an accuracy of 0.2sec. If the observer
stations himself inconspicuously, the speed readings are not influenced by driverreaction.
The disadvantage of this method is errors due to the parallax effect. Parallax is a
displacement or difference in the apparent position of an object viewed along two
different lines of sight. 5
7/28/2019 3A Traffic Studies
6/38
KAAF UNIVERSITY COLLEGE
Manual Method of Measuring
Spot Speed
A simple device called Enoscope eliminates the parallax effect that creeps in when
the direct readings are taken by one observer.
The instrument bends the line of sight of the observer so that it is perpendicular to the
path of the vehicle.
The stop watch is started as soon as the vehicle passes the first reference point and
is stopped as soon as it passes the observer.
6
7/28/2019 3A Traffic Studies
7/38
KAAF UNIVERSITY COLLEGE
Automatic Method of Measuring
Spot Speed
Automatic methods can be categorized under
1. Road detectors
2. Radar guns
3. Photographic and video camera
Road Detectors
They can be categorized into pneumatic road tubes and inductive loops. They can
also be used to collect volume data apart from speeds.
The advantage of the detector meters is that human errors are considerably reduced.
The following advantages are associated with them;
1. The devices are expensive
2. Where pneumatic tubes are used, they are rather conspicuous and may,
therefore affect driver behaviour, resulting in a distortion of the speed distribution.
7
7/28/2019 3A Traffic Studies
8/38
KAAF UNIVERSITY COLLEGE
Automatic Method of Measuring
Spot Speed
Radar Guns
They work on the principle that when a signal is transmitted onto a moving vehicle,
the change in frequency between the transmitted signal and the reflected signal is
proportional to the speed of the moving vehicle.
The advantage of this method is that it can be located at an inconspicuous position
where the influence on driver behaviour is considerably reduced.
Photographic and video camera
Time lapse camera photography has been used successfully to determine the
speeds of vehicles accurately. By this method photographs are taken at fixedintervals 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 also be used.
The major advantage is that one needs not to physically install a device like
pneumatic tube or loop on the road.8
7/28/2019 3A Traffic Studies
9/38
KAAF UNIVERSITY COLLEGE
Analysis and PresentationSpot Speed
Average Speed : This is the arithmetic mean of all observed vehicle speeds ( which
is the sum of all spot speeds divided by the number of recorded speeds. It is given
by ;
Where = arithmetic mean
fi = number of observations in each speed group
ui= mid value for the ith speed group
Median: This is the speed at the middle value in a series of spot speeds that are
arranged in ascending order. 50% of the speed values will be greater than the
median; 50% will be lesser than the median
Modal Speed: This is the speed value that occurs most frequently in a sample of
spot speeds.
9
7/28/2019 3A Traffic Studies
10/38
KAAF UNIVERSITY COLLEGE
Analysis and PresentationSpot Speed
The ith percentile spot speed : This is the spot speed value below which i percent
of the vehicles travel; for example, 85th percentile spot speed is the speed below
which 85 percent of the vehicles travel and above which 15 percent of the vehicles
travel.
Pace: This is the range of speed, usually taken at 10 mi/h that has the greatest
number of observations.Standard Deviation : It is a measure of the spread of the individual speeds.
S = standard deviation
= arithmetic mean
Ui = mid value of speed class i
fi = frequency of speed class i
N = Number of observations
10
7/28/2019 3A Traffic Studies
11/38
KAAF UNIVERSITY COLLEGE
ExampleSpot Speed
11
7/28/2019 3A Traffic Studies
12/38
KAAF UNIVERSITY COLLEGE
ExampleSpot Speed
12
7/28/2019 3A Traffic Studies
13/38
KAAF UNIVERSITY COLLEGE
Volume Count Units I
The common types of counts include;
Average Annual Daily Traffic (AADT)
It is the average of 24 hour counts collected everyday in the year. It represents 1/365
of the total annual flow. It is often used for estimating the total travel on a road
system and for determining the gross annual revenues from road users. It is also
used as standard for pavement design and maintenance.
Average Daily Traffic (ADT)
It is the average of 24 hour counts collected over a number of days greater than 1 but
less than a year. They are often needed for measurement of current demand and
evaluation of existing traffic flow.
Peak Hour Volume (PHV)It is the maximum number of vehicles that pass a point on a highway during a period
of 60 consecutive minutes. PHVs are often used for
Functional classification of highways
Capacity analysis (lane number, signal time, channelization)
Development of parking regulations13
7/28/2019 3A Traffic Studies
14/38
KAAF UNIVERSITY COLLEGE
Volume Count Units II
Vehicle Classification (VC)/ Classified Counts
Volumes are recorded with respect to the type of vehicles eg. Passenger cars, two-axle trucks,
or three-axle trucks. GHA has the following categories of vehicles Categories of Vehicles
Counted.jpg and a typical count sheet is Classified Count Sheet.jpg. They are important for
geometric design characteristics eg. Turning radii, maximum grades, lane widths etc. Also for
structural design of pavements. Example of PHV and Classified Count.docx
Passenger Car Units (PCU)/ Passenger Car Equivalence (PCE)
It converts the volume into equivalent passenger car units where traffic is composed of a
number of type of vehicles by using equivalency factors. It shows the impact that a mode of
transport has on traffic variables (such as headway, speed, density) compared to a single car.
They are often used in the determination of highway capacity.
American Unite Kingdom
private car (including taxis or
pick-up) 1
motorcycle 0.5
bicycle 0.2
horse drawn vehicle 4bus, tractor, truck 3.5
Motorbike 0.4
Car 1.0
LGV 1.0
RGV 1.9
Articulated goods vehicle 2.9PSV (bus) 2.5
14
http://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Example%20of%20PHV%20and%20Classified%20Count.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Classified%20Count%20Sheet.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2/Categories%20of%20Vehicles%20Counted.jpg7/28/2019 3A Traffic Studies
15/38
KAAF UNIVERSITY COLLEGE
Volume Count Units III
Vehicle Miles of Travel (VMT)
This is a measure of travel along a section of road. It is the product of the traffic
volume and the length of road way to which the volume is applicable. VMTs are used
mainly as a base for allocating resources for maintenance and improvement of
highways. It is also used in determining level of vehicle emissions.
Find out the following;
What is passenger km and when it is often used.
What is Passengers per bus hour and when it is often used.
15
7/28/2019 3A Traffic Studies
16/38
KAAF UNIVERSITY COLLEGE
Methods of Conducting Volume
Counts I
There are two main methods of conducting volume counts which are namely; Manual
Counts and Automatic Counts. Benefits of each include
Manual Counts
Details such as vehicle classification and number of occupants can be easily
obtained. Unusual conditions obtained during time of count can be recorded.
In developing countries where automatic devices are hard to come by this method is
comparatively cheap.
They easily compliment and can serve as a check on the accuracy of data collected
by automatic means.
Automatic Counts
Where continuous and regular record of traffic flow is needed, the only alternative isto use automatic counts
If counts of remote areas are needed, automatic devices are useful
They yield data which is amenable to easy analysis by computers.
What are the disadvantages of both methods?
16
7/28/2019 3A Traffic Studies
17/38
KAAF UNIVERSITY COLLEGE
Manual Counts I
Involves one or more persons recording observed vehicles using a counter.
Considerations
Link counts should be located on straight sections of road for good visibility. Duration
can be from a few minutes to several days, depending on purpose. Most counts are
carried out for one day, starting before the morning peak hour, and extending for 12,14 or 16 hours. Count periods are usually 15 minutes, with results summarised
hourly.
In Turning movement counts the vehicle classification system is simplified (to
compensate for the extra demands on Surveyors). These surveys are primarily
concerned with the performance of the junction during peak periods. Count periods
are usually 15 minutes. However, at signalised junctions short-term volumes are
determined by signal operations, and cycle times in excess of 2 minutes, or count
periods less than 15minutes, may cause apparent fluctuations in flow. In such cases
it is best to record flow for each cycle, using the cycle time as the counting period.
17
7/28/2019 3A Traffic Studies
18/38
KAAF UNIVERSITY COLLEGE
Manual Counts II
Survey Forms
Pencil and Paper method; -The 'five-bar gate' method is the most versatile and is
applicable to both link and turning counts. It records data quickly(without the need for
extreme neatness), is the most economical in use of space on the survey form and
can be summarised quickly.
Alternatively, hand tallies can be used to record specific vehicle classes. They arefaster and more accurate than pencil and paper methods, because only the total is
recorded, at the end of each count period, and the surveyor is looking at the traffic
flow almost continuously. However, vehicles can be missed while recording the
cumulative total at the end of each count period.
Equipment Needed
1. A watch 2. Pencils, eraser and pencil sharpener 3. Supply of blank field data
sheets 4. Clipboards
Errors in Manual Counts
1. Failure to define vehicle classification unambiguously
2. Failure to observe time periods accurately
3. Surveyors having to count vehicles at a faster rate. 18
7/28/2019 3A Traffic Studies
19/38
KAAF UNIVERSITY COLLEGE
Manual Counts III
19
7/28/2019 3A Traffic Studies
20/38
KAAF UNIVERSITY COLLEGE
Automatic Counts I
Automatic traffic counter equipment consists of a detector, to detect the vehicle, and
a counter to record the information. The most common types of detector used in
traffic counting are a hollow rubber pneumatic tube, held to the road surface by
special clips, or an inductance loop (several turns of wire laid on or in the road
surface in a rectangular or diamond shape).
Pneumatic Tubes
Pneumatic tubes detect the movement of a vehicle as the tube is depressed by a
tyre; this creates a pulse of air which closes a diaphragm in the recorder. The count
site must not be located where braking or acceleration occurs, or where overtaking is
common, such as near junctions, bus stops, or other parking locations.
Why should pneumatic tubes not be located where braking or acceleration occurs or
where overtaking is common?
20
7/28/2019 3A Traffic Studies
21/38
KAAF UNIVERSITY COLLEGE
Automatic Counts IIPneumatic Tube
21
7/28/2019 3A Traffic Studies
22/38
KAAF UNIVERSITY COLLEGE
Automatic Counts IIIInductive Loops
A loop detector detects the presence, rather than the movement of a vehicle.
The counter passes an alternating electric current through the loop, creating a
magnetic field above the loop. The presence of a metal vehicle in the magnetic field
causes a change in the electrical inductance, which is recorded by a sensor in thecounter.
Non-metallic vehicles cannot be detected and pedal cycles are very difficult to detect
because of their shape. Loops are usually permanent installations, laid in a shallow
slot cut into the road surface, and sealed in by epoxy resin and bitumen. However,temporary loops can be fixed with sticky tape to the road surface.
22
7/28/2019 3A Traffic Studies
23/38
KAAF UNIVERSITY COLLEGE
Automatic Counts IVInductive Loops
23
7/28/2019 3A Traffic Studies
24/38
KAAF UNIVERSITY COLLEGE
Types of Volume Counts
Cordon Counts
A cordon is an imaginary boundary around a study area. It is generally established to
define a CBD or other major activity centre where the accumulation of vehicles within
the area is of great importance in traffic planning. The intersection of each street
crossing the cordon line is taken as a count station; volume counts of vehicles or
persons entering and leaving the cordon area are counted.
24
7/28/2019 3A Traffic Studies
25/38
KAAF UNIVERSITY COLLEGE
Types of Volume Counts
Cordon counts are useful for
Planning parking facilities
Updating and evaluating traffic operational techniques
Making long range plans for freeway and arterial facilities
Screen Line Counts
In screen line counts the study area is divided into large sections by running
imaginary lines, known as screen lines, across it.
Natural and man made barriers such as rivers or railway tracks are often used.
Traffic counts are taken at each point where a road crosses the screen line. It is
important for the screen line not to be traversed by the same road several times.
Often these counts are done to determine the variations in the traffic volume and
traffic flow direction due to change in land use pattern of the area. 25
7/28/2019 3A Traffic Studies
26/38
KAAF UNIVERSITY COLLEGE
Types of Volume Counts
Intersection Counts
They are taken to determine vehicle classification through movements and turning movements
at intersections. The data obtained from this count is useful for ;
Determining phase lengths and cycle time for signalised intersections.
Design of channelisation at intersections
Design improvements of intersectionsPedestrian Volume Counts
Volume counts of pedestrians are made at locations such as intersections, along sidewalks and
midblock crossings, overpasses, underpasses etc.
Data from this count could be used for crash analysis , capacity analysis, and determining
minimum signal timings at signalised intersections.
Periodic Volume CountsTo make reasonable estimates of annual traffic volume characteristics on an area wide basis,
different types of periodic counts, with count durations ranging from 15 minutes to 60 continuous
,are conducted. The various periodic counts conducted include continuous, control and
coverage counts.
26
7/28/2019 3A Traffic Studies
27/38
KAAF UNIVERSITY COLLEGE
Example of Network Count
A represents the continuous count station
1-6 represents the control stations 1 6.
Two set of crew to do the counting from 12pm to 8pm.
27
7/28/2019 3A Traffic Studies
28/38
KAAF UNIVERSITY COLLEGE
Scenario 1 One Day Study
Assumptions-One crew will be used to count control location A for the entire 8 hour period of the study.
-The second crew would be used to count each of the coverage locations 1 6 for 1 hour
28
7/28/2019 3A Traffic Studies
29/38
KAAF UNIVERSITY COLLEGE
Scenario 1 One Day Study
29
7/28/2019 3A Traffic Studies
30/38
KAAF UNIVERSITY COLLEGE
Scenario 2 Six Day Study Count
Assumptions
-Each coverage station is to be counted for 8 hours.
-One crew monitors the control station and the other crew 8 hours each day on each coverage
station.
30
7/28/2019 3A Traffic Studies
31/38
KAAF UNIVERSITY COLLEGE
Scenario 2 Six Day Study Count
31
7/28/2019 3A Traffic Studies
32/38
KAAF UNIVERSITY COLLEGE
Periodic Counts
Continuous Counts. These counts are taken continuously using mechanical or electroniccounters. In selecting stations where continuous counts are done (permanent count stations)
the highways within the study area must first be properly classified. Thus links should be
categorized according to similar traffic characteristics such as AADT and daily, weekly and
seasonal variations in traffic volumes.
Control Counts. These counts are taken at stations known as control count stations whichare strategically located so that representative samples of traffic volume can be taken on each
type of highway or street in an area wide traffic counting program. The data obtained from
control counts are used to determine seasonal and monthly variations of traffic characteristics
so that expansion factors can be determined. Control counts can be divided into major and
minor control counts. Major control counts are taken monthly, with 24-hr directional counts taken
on at least three days during the week ( Tues, Wed, Thurs) and also on Saturday and Sunday
to represent the weekend.Coverage Counts. These counts are used to estimate ADT, using expansion factorsdeveloped from control counts. The study area is usually divided into zones that have similar
traffic characteristics. At least one coverage count station is located in each zone. A 24-hr non
directional weekday count is taken at least once every 4 years at each coverage station. It tells
changes in area wide traffic characteristics.
32
7/28/2019 3A Traffic Studies
33/38
KAAF UNIVERSITY COLLEGE
Adjustment of Periodic Counts
Expansion factors, used to adjust period counts, are determined either from continuous count
stations or from control count stations. Hourly, daily, and monthly expansion factors can be
determined using data obtained at continuous count stations.
Hourly Expansion Factors (HEF)
These factors are used to expand counts of duration shorter than 24-hr to 24-hr volumes by
multiplying the hourly volumes for each hour during the count period by the HEF for that hour
and finding the mean of these products.
HEF = total volume for 24-hr period
volume for particular period
Daily Expansion Factors (DEF)These factors are used to determine weekly volumes from counts of 24-hr duration by
multiplying the 24-hr volumes by the DEF
DEF = average total volume for the week
average volume for particular day
33
7/28/2019 3A Traffic Studies
34/38
KAAF UNIVERSITY COLLEGE
Adjustment of Periodic Counts
Monthly Expansion Factors(HEF)
The AADT for a given year may be obtained from the ADT for a given month by multiplying this
volume by the MEF
MEF= ________AADT____________
ADT for particular month
Example of Daily Expansion Factors
34
7/28/2019 3A Traffic Studies
35/38
KAAF UNIVERSITY COLLEGE
Adjustment of Periodic Counts
Monthly Expansion Factors (MEF)
35
7/28/2019 3A Traffic Studies
36/38
KAAF UNIVERSITY COLLEGE
Presentation of Volume Data
Traffic Flow Maps
These maps show traffic volumes on individual routes. The volume of traffic on each
route is represented by the width of a band, which is drawn in proportion to the traffic
volume it represents, providing a graphic representation of the different volumes that
facilitates easy visualisation of the relative volumes of traffic on the different routes.
36
7/28/2019 3A Traffic Studies
37/38
KAAF UNIVERSITY COLLEGE
Presentation of Volume Data
Intersection Summary Sheet
These sheets are graphic representations of the volume and directions of all traffic
movements through the intersection
37
7/28/2019 3A Traffic Studies
38/38
KAAF UNIVERSITY COLLEGE
Presentation of Volume Data
Time Base Distribution Charts
These charts show the hourly, daily, monthly or annual variations in traffic volume in
an area or on a particular highway.
38