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Traffic Monitoring: A Guidebook
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3. Traffic Monitoring 101
- What Does Traffic Monitoring Do for Me?
- What Resources Are Available?
- What Are the Types of Traffic Monitoring?
What Does Traffic Monitoring Do for Me?
Traffic monitoring can provide travel related information to anyone needing to make informed decisions based on travel pattern information. The information obtained from the collection of traffic data can assist in finding solutions to transportation related problems once the extent and magnitude of that problem has been identified. Traffic monitoring can also be used to determine improvements to various transportation facilities based on the collection of accurate information in order to present a clear and objective description of how a facility operates.
What Resources Are Available?
There are multiple resources available to assist in the development of a useful and successful traffic monitoring program. Most of these resources were developed by engineering and transportation professionals to assist in the design, construction, and operation of the highway system. These same strategies can be applied to most instances where traffic related information is being collected. Several of the most informative resources pertaining to traffic monitoring guidance include the following web sites and/or publications:
Federal Highway Administration
- Travel Monitoring. Policy information webpage.
- Traffic Monitoring Guide. FHWA-PL-01-021.
- Traffic Detector Handbook: Third Edition. FHWA-HRT-06-108.
- Highway Performance Monitoring System Field Manual for the Continuing Analytical and Statistical Database.
Institute of Transportation Engineers
- Manual of Transportation Engineering, 1994.
- Traffic Engineering Handbook, 4th Edition, 1992
What Are the Types of Traffic Monitoring?
There are several types of traffic monitoring alternatives that can be carried out depending on the anticipated use of the data to be collected. These types of alternatives include vehicle volume counts which range from short term counts to continuous counts, vehicle classification and occupancy counts, truck weight counts, pedestrian counts, bicycle counts, and others that may be determined for a specific need. These different counts will be discussed in the following sections.
Vehicle Volume Counts
Vehicle volume counts can provide a vast amount of information which can assist in the decision making processes related to a highway or a system of highways. The data obtained provides an estimate of the number of vehicles traveling a section of highway over a specified period of time. Typically vehicle volume counts will be in the range from short term counts to long term continuous counts.
Short Term Counts at a Large Number of Locations
Short term counts are vehicle volume counts that are performed for intervals less than an hour (e.g., 5, 15, 30 minutes). It is not feasible to collect continuous data on all roadways due to the cost involved. Short term volume counts allow for a larger number of locations to be surveyed given that the counting equipment is not monopolized by just a few locations. Short term volume counts are typically used to determine peak volume characteristics or to estimate annual traffic characteristics. Short term counts are typically performed manually by observation or with portable automatic counting equipment.
Continuous Counts at Select Locations
Continuous counts are vehicle volume counts that are performed for longer intervals (e.g., daily, weekly, and seasonally). These counts are carried out on a continuous basis utilizing automatic counting equipment and are sometimes referred to as permanent count stations. Continuous volume counts allow for a fewer number of locations to be surveyed since the counting equipment is generally permanent and is continuously operating at a limited number of locations. Continuous volume counts are typically used to determine fluctuations in weekly/seasonal traffic or to determine growth rates of traffic.
| TYPES OF VEHICLE VOLUME COUNTS | |||
|---|---|---|---|
| SHORT TERM COUNTS | PEAK-HOUR COUNTS | 24-HOUR COUNTS | CONTINUOUS COUNTS |
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Source: North Central Texas Council of Governments
The chart above summarizes the range of vehicle volume counts available and the respective purpose and use of each.
Vehicle Classification/Occupancy Counts
Vehicle classification counts are counts that determine the type of vehicle at a count location and are useful in determining seasonal variations. These counts can be performed manually through classifying the vehicle type by visual observation or by automatic counting equipment that measures the length of a vehicle or that measures the number of axles on a vehicle, depending on the type of sensor used. Vehicles are typically classified into 13 vehicle classification categories as defined by Federal Highway Administration (FHWA). However, vehicle classification categories can be changed to accommodate other reporting needs, such as in parks and recreational areas where vehicle types may significantly differ from customary roadway usage.
| NPS CLASS | FHWA CLASS |
|---|---|
| Motorcycles | Class 1: Motorcycles |
| Passenger Cars | Class 2: Passenger Cars |
| Recreational Vehicles | Not Applicable |
| Vehicles/RV pulling Trailer | Not Applicable |
| Transit/Shuttle Bus | Class 4: Buses |
| Tour Buses | Class 4: Buses |
| Light-Duty Trucks | Class 3: Other two-axle, four-tire single unit vehicles Class 5: Three-axle, six-tire, single-unit trucks |
| Heavy-Duty Trucks | Class 6: Three-axle single-unit trucks Class 7: Four or more axle single-unit trucks Class 8: Four or fewer axle single-trailer trucks Class 9: Five-axle single-trailer trucks Class 10: Six or more axle single-trailer trucks Class 11: Five or fewer axle multi-trailer trucks Class 12: Six-axle multi-trailer trucks Class 13: Seven or more axle multi-trailer trucks |
Vehicle occupancy counts
Vehicle occupancy counts are counts that determine the number of people in each vehicle at a count location and help in determining travel modes and person movement within a region. These counts are usually performed manually by personnel monitoring from the roadside. It is customary to concurrently determine the vehicle classification and the number of people in each respective vehicle while conducting vehicle occupancy counts.
Truck Weight Counts
Truck weight counts are counts that determine vehicle weight loads and are useful in determining where heavy loaded vehicles are traveling. These counts are performed by automated equipment known as weigh-in-motion (WIM) detectors. Sites chosen for this type of detector generally reveal directional rutting in pavements; increased truck traffic and/or high proportion of trucks; proximity to special truck traffic generators; and seasonal influences of heavy loads (11).
Pedestrian Counts
Volume counts of pedestrians are made at locations such as sidewalks, cross walks, and transit stations. The counts are performed manually and are usually taken at these locations when the evaluation of existing or proposed pedestrian facilities is being considered. Pedestrian activity can be a major component in the safety, design, and operation of sidewalks, bridges, and underpasses.
Bicycle Counts
Volume counts of bicycles are made at locations with high bicycle activity such as parks and recreational areas. The counts are performed manually and are usually taken along trail sections, bicycle lanes, or at bicycle staging locations. These counts assist in determining the impacts bicycles have when interacting with other modes of travel, such as at intersections, and in planning for future amenities related to bicycling.
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