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Travel time, or the time required to traverse a route between any two points of
interest, is a fundamental measure in transportation.
Travel time is a simple concept understood and communicated by a wide variety of
applications for transportation engineers and planners.
Several data collection techniques can be used to collect travel times.
These techniques are designed to collect travel times and average speeds on
designated roadway segments or links.
Following are the different techniques available for the travel time data
collection.
- Test Vehicle Techniques
- License Plate Matching Techniques
- ITS Probe Vehicle Techniques
- Emerging and Non-Traditional Techniques
Travel time data using active test vehicles in combination with varying levels
of instrumentation: manual (clipboard and stopwatch), an electronic distance
measuring instrument (DMI), or a global positioning system (GPS) receiver.
It involves the use of data collection vehicle within which an observer records
cumulative travel time at predefined checkpoints along a travel route.
Then this information converted to travel time, speed, and delay for each
segment along the survey route.
There are several different methods for performing this type of data collection,
depending upon the instrumentation used in the vehicle.
These vehicles are instrumented and then sent into the field for travel time
data collection, they are sometimes referred to as ``active'' test vehicles.
Advantages
- Advanced test vehicle techniques (e.g., DMI or GPS use) result in detailed
data.
- Low initial cost.
Disadvantages
- Sources of possible error from either human or electric sources that
require adequate quality control,
- Data storage difficulties.
Travel times by matching vehicle license plates between consecutive checkpoints
with varying levels of instrumentation: tape recorders, video cameras, portable
computers, or automatic license plate character recognition.
Advantages
- Travel times from a large sample of motorists, very simple technique.
- Provides a continuum of travel times during the data collection period.
Disadvantages
- Travel time data limited to locations where observers or video cameras can
be positioned;
- Limited geographic coverage on a single day
- Accuracy of license plate reading is an issue for manual and portable
computer
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