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A Journey Time Survey is a process whereby a vehicle is driven along
a designated stretch of road and various parameters such as Time,
Distance, Speed, and Fuel Consumption are recorded. These parameters are
then analysed to determine the quality of traffic flow that exists on
the road.
The Traffic and Transportation Department has developed an in-house
software suite called the Journey Time Survey System.
This software suite is made up of two sub-systems
- the Journey Time Machine package
- the Journey Time Analysis package
The Journey Time Machine is connected to distance and fuel
transducers located in a motor vehicle. These two parameters, distance
travelled and the consumption of fuel, are recorded and related to time
by the Journey Time Machine software as the vehicle is driven along the
road. The recorded data can then be transferred to the Journey Time
Analysis package for analysing.
The collected data can be viewed either as single runs, or else in
three dimensions using multiple runs. It is also possible to create an
average run from a number of runs, and to statistically compare two
groups of runs.
The system was designed to assist the traffic engineer in locating
the areas and the time periods of traffic congestion; for determining
the causes of congestion; and for statistically evaluating the effect of
traffic improvement methods.
Conducting a Survey
There are two ways of conducting a Survey using the Journey Time
Machine package :
- Manual Survey
- Automatic Survey
A manual survey involves driving the route and pressing the function
keys at each key point in the same way as was done during the
preparation phase. This can possibly mean that a separate operator is
required in the car so as not to hinder the driver.
An automatic survey can easily be handled by the driver of the
vehicle alone as minimum input is required. The driver must simply
select the Survey to be run before starting, and the Computer then logs
the keypoints at the pre-defined distances, and stops collecting data at
the end point. All other parameters are entered at some time before the
actual Survey, and stored on the hard disk.
During a survey run, accuracy will be improved if weaving is avoided
and lane changes, if required, are done in the same place by each
vehicle taking part.
For sample standardization it is important that a common method of
driving is maintained by all the drivers taking place. This method can
be one of the following:
- Floating-Car technique - overtake as many vehicles as pass the
driver's car
- Average-Car technique - drive according to the driver's judgement
of the average speed of the traffic
- Maximum-Car technique - drive at the speed limit unless impeded by
other traffic
Once a Survey is complete, the recorded data must be copied to a
removable disk using the Data Transfer option, for transfer to the
Journey Time Analysis package.
The Survey data can also be copied to an ASCII file, if necessary,
for import into a spreadsheet.
Analysing the Survey Data
Importing The Data
Survey Runs imported from the Journey Time Machine are stored in
groups on the Journey Time Analysis computer. These groupings are
determined by the Survey Label that was used on the Journey Time
Machine.
Methods of Analysis
There are various ways of viewing the collected data, and the correct
approach depends the user's requirement.
Each individual run can be viewed in detail, if necessary, and exact
delays and queue lengths can be measured.
Multiple runs can be viewed either as a Distance/Time/Speed contour
plot, or as a statistical sample showing the mean and standard deviation
of each parameter.
If a number of runs have been recorded along a route, with reasonable
headways between each run, then the first option to select would
typically be the Data Analysis - Multiple Runs
option. This would give the user an overall picture of the conditions on
the route and how they changed with time. Areas of congestion can easily
be identified and the user could then use the Data Analysis - Single
Run option to zoom in on the these areas to gain further insights
into the situation.
The
Data Analysis - Statistical Analysis option is normally used to
compare two collections of Survey runs; typically for a 'Before and
After' study.
The resultant displays from each of these options can be output to a
printer.
Typical Applications
Journey time surveys are useful in evaluating the general efficiency
of traffic movement within an area or along selected routes.
The following are a few typical applications.
- Evaluation of the efficiency of Signal Timings.
- Determination of the Average Running Speed in a congested
area.
- Comparison of Alternate Routes.
- Monitoring of Travel Speed Trends by periodic sampling of major
routes.
- Identification of areas of Congestion and Speeding.
- Evaluation of the effectiveness of traffic improvements by
conducting Before and After Studies.
- Calculation of Road-User Costs in the economic analysis of highway
and traffic improvements.
- Establishment of Link Travel Times or Speeds for the use in traffic
models.
The method to use in doing a journey time survey will vary depending
on the type of study being undertaken, the number of equipped vehicles,
the personnel involved, and the funds or time available
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