Traffic studies Flashcards
the most basic data needed for any traffic studies.
Traffic volume
conducted to obtain factual information on the number of vehicles and/or persons that pass at a
specified point on the highway system.
Volume studies
Types of Volume
a. Annual daily traffic/Annual traffic
b. Annual average daily traffic (AADT)
c. Hourly traffic
d. Short-term count
used for determining annual travel, estimating expected highway
user revenue, computing accident rates.
obtained by conducting traffic volume counts over
a number of days at least two days and less than 365 days.
Annual traffic
used for measuring the present demand for
service by the road, programming capital improvements.
Annual average daily traffic (AADT)
used for evaluating capacity deficiencies, geometric design or
improvement of streets and intersections.
Hourly traffic
used to estimate maximum flow rate and determine the
characteristics of peak hour volumes.
Short-term count
Types of Data Collected
a. Mid-block counts
b. Directional counts
c. Turning movement or intersection counts
d. Classification counts
e. Cordon counts
f. Screen line counts
used for preparing traffic flow maps and determining trends.
Mid-block counts
used for determining directional distribution for capacity analysis,
signal timing, justifying traffic control, etc.
Directional counts
used for signal timing, designing or
improving geometry of intersection, planning turning prohibition, analyzing high
accident intersections.
Turning movement or intersection counts
used for determining modal split, estimating effects of heavy
vehicles on capacity, determining correction factors for automatic counts.
Classification counts
used to determine the number of vehicles and/or persons entering and
leaving an enclosed area.
Cordon counts
classified counts taken at some points along a line that bisects a
given area.
Screen line counts
The time and duration of a traffic volume study depends on the type and application of the
data to be gathered. Some of the typical counts are as follows:
a. Twenty-four-hour counts from midnight to midnight
b. Sixteen-hour counts from 6 AM to 10 PM to represent most of daily flow, including evening
traffic
c. Twelve-hour counts from 6 AM to 6 PM to cover most of daytime traffic
d. Peak period counts from 7 AM to 9 AM, 5 PM to 7 PM, or other time intervals corresponding to
very high level of traffic volume
e. Short counts of about one hour or less with intervals of 5-15 minutes to analyze
characteristics of peak hours.
Abnormal conditions are usually avoided unless the purpose is to obtain information
concerning those conditions. These would include
a. special occasions such as public holidays or fiestas
b. days with abnormal weather conditions
c. strikes or demonstrations.
Methods of volume studies
A. By tallying
B. Using manual counters
C. Using automatic counters
D. Using video cameras
This is the simplest and sometimes most practical in the absence of any mechanical or
automatic counting device.
Tally sheets are used to record the number of vehicles.
The method may be
used when traffic volume is generally low or when observing a particular turning movement whose
volume is relatively low.
tallying
a mechanical device useful when volume is high. Counters
may he of single or multiple type.
manual counter
When traffic count of very long duration is required, ____________ through
the use of detectors may be used.
automatic counters
The simplest type of an automatic counter is a
___________ laid transversely across the road.
More sophisticated detectors make use of ultrasonic waves or
inductance loops.
pneumatic tube
may be used to take footage of the traffic flow.
Video cameras
Presentation of Traffic Volumes
a. Variations
b. Flow Maps
c. Intersection Diagram
has been a common measure of daily traffic at
a given location. At a given point along a particular highway, it is estimated as the total volume
counted over one year divided by the number of days in the year,
annual average daily traffic or AADT
This is obtained by
conducting traffic volume counts over a number of days at least 2 days and less than 365 days.
average daily traffic or ADT.
is programming the conduct of such counts in
such a way at to have good estimates of AADT for all national highways by applying some
seasonal factors.
Department of Public Works and Highways
are useful in highway planning or in prioritizing
some maintenance or repairs of roads.
However, they cannot be used along for design or
operational analysis purposes because in many cases, the traffic volume varies greatly
throughout the day.
Daily volumes, AADT
The objectives of conducting spot speed studies are to
a. determine the range and magnitude of speeds as a basis for formulating the design
standards,
b. establish maximum and minimum speed limits,
c. determine the need for posting advisory speed signs,
d. determine the need for school zone protection, and
e. evaluate the performance of a geometric improvement or traffic control device through a
“before-and-after” study.
Abnormal conditions such as adverse weather condition or unusually heavy traffic condition
should be avoided.
Time of SPOT SPEED STUDIES
The duration of the study should be around one hour. Short study period will
often lead to bias towards faster vehicles.
Time of SPOT SPEED STUDIES
Normally, the speeds of at least __________ should be measured.
50 vehicles – preferably 100
To cover all representative vehicles, measurement of every nth vehicle may be applied. In this way,
bias that may be attributed to the following may be avoided:
a. Selecting mostly leaders of the platoon
b. Selecting mostly one particular type of vehicle
c. Selecting faster vehicles
Methods for conducting spot speed studies
Radar speed meter
Manual method/“trap length” method
is very convenient way of conducting
spot speed studies.
Radar speed meter
is positioned at the edge of the roadway at an angle of 15 degrees with the centerline and is directed toward the incoming vehicles.
Radar speed meter
maybe difficult to use
when volume of traffic is high.
often used by police authorities for
apprehending over speeding drivers.
Radar speed meter
A very useful and less expensive way of conducting spot speed studies
two lines, 30-50 m apart, are drawn transversely on the pavement. A stopwatch is then used to measure the “travel time” of the vehicle within the “trap”.
The length of the trap is divided by the travel time estimate the speed. The observer must be well
trained in order to reduce error attributed to parallax, a common error in most visual methods of
conducting surveys.
“trap length” method
An alternative to conducting spot speed directly in the field is to take video of the traffic
flow and watch it at a later time in the office. Markings on the pavement may be drawn before
the video is taken. Another way is to put markers on the roadside that will help draw the “trap”
on the TV screen or monitor.
Manual method
are usually summarized in a frequency table. Data are normally grouped
together in predetermined class intervals, and distributions are calculated.
Spot speed data
may serve as a guide in determining the initial number of class intervals.
Sturgess formula
Sturgess formula
k = 1+ 3.322 log10 n
normally give information on the performance of a particular
roadway. Independent measurements of stops and their observed reasons may also be included to
give information on delays.
Travel time studies
Methods in TRAVEL TIME AND DELAY STUDIES
Test car technique
Licensed plate method
The method makes use of a test vehicle that is driven over the road section under study.
The driver is instructed to travel at a speed that in his opinion is representative of the speed of the
traffic stream.
Test car technique
When details on delay are not important, the _____________ may be conducted. The
method basically consists of observing and recording license plates of vehicles and time of
arrivals at two points or more on the road where the vehicles are expected to pass.
license plate method
It may be convenient to divide the time of observation into _____________ intervals.
Within each interval the license plates of vehicles passing the point of observation are recorded.
If traffic volume is heavy, it may be very difficult to observe and record the complete license
plate number. It may be more practical to just record the ________________.
5- or 10-minute
first letter and the last three digits
