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Traffic volumes vary over time on all roads.
Traffic volumes also vary dramatically from one road to another.
These variations in traffic volume are even more apparent when volumes for
specific vehicle types (classification) are analyzed.
Consequently, the vehicle classification data collection program must gather
sufficient data on traffic patterns of important vehicle types to accurately
quantify the truck traffic stream to meet the needs of users.
These include; time of day, day of week, time of year, direction.
Vehicle classification counts are used in establishing structural and geometric
design criteria, computing expected highway user revenue, and computing
capacity.
If a high percentage of heavy trucks exist or if the vehicle mix at the crash
site is suspected as contributing to the crash problem, then classification
counts should be conducted.
Typically cars, station wagons, pickup and panel trucks, and motorcycles are
classified as passenger cars.
The observer records the classification of vehicles and its direction of travel
at the intersection.
The vehicle classification counts required should not be considered separate
from the volume counts traditionally performed.
Instead, they should be integrated with the traditional volume counts.
Because classification counts provide both classification and total volume
information, they can replace traditional volume counts reducing duplication and
error.
Traffic surveillance equipment is used as part of advanced traffic management
systems (ATMS) or advanced traveler information systems (ATIS) can be used to
supply both total volume and vehicle classification information.
Intelligent transportation system (ITS) technology and its resulting data are
often present at high profile locations as part of safety enhancement systems.
These systems can supply useful, continuous traffic monitoring data.
Coordinating these traffic monitoring activities can lead to significant
improvements in the amount of data available to users, while at the same time
reducing the cost of data collection.
Vehicle classification data are of considerable use to agencies involved in
almost all aspects of transportation planning and engineering.
The need for information on truck volumes and freight movements is growing with
the recognition of role that freight mobility plays in the economy, and as
highway engineers realize the importance of truck volume and operating
characteristics on the geometric and structural design of roadways and bridges.
- pavement design
- pavement management
- scheduling the resurfacing, reconditioning, and reconstruction of highways
- prediction and planning for commodity flows and freight movements
- development of weight enforcement strategies
- vehicle crash record analysis
- environmental impact analysis
- analysis of alternative highway regulatory and investment policies.
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