Traffic Monitoring Program
The Data Collection and Reporting Section at MDOT collects, analyzes, summarizes, reports, and retains detailed traffic data and travel information for 36,000 miles of federal-aid roads in Michigan, with additional reporting requirements for the 83,000 miles of local roads. Traffic data collection consists of short-term counts/studies, year-round data from the continuous count sites, and special studies. The data collected is provided to the Federal Highway Administration (FHWA) on a monthly and annual basis. The data is also used to drive decisions being made by other MDOT divisions, Michigan State Police, the Transportation Asset Management Council, and local agencies. The section also plays a pivotal role in helping to meet the data collection and reporting required by the FHWA’s Highway Performance Monitoring System (HPMS) on all federal-aid roads.
Traffic Counts Collection (Trunkline and Non-Trunkline Roads)
- MDOT collects traffic data, in the form of traffic counts, on all trunkline (federal-aid) roads and works with individual local agencies (cities/villages, counties, metropolitan planning organizations and regional planning agencies) to collect traffic data for non-trunkline roads via the Non-Trunkline Federal Aid Road Program (NTFA).
- There are two primary types of traffic counts that are used by MDOT: short counts and continuous counts. Short counts are the most common as they are easy to set up and cheap to maintain but only collect snippets (generally over a 48-hour period) of traffic moving through a designated location (where the station is set up). Continuous counts are designed to collect traffic counts 24 hours a day, seven days a week, for all 365 days in a year. They are costlier to maintain compared to short counts and are set up in different regions throughout the state to get as much variety in the traffic data collected via continuous counts as possible but provide far more accurate and detailed data compared to short counts. The data gathered from continuous counts are used to create factors (seasonal factors for example), which are utilized in a process of normalizing short count data.
Average Annual Daily Traffic (AADT)
- AADT is the estimated mean daily traffic volume. For continuous count sites, it is calculated by summing the Annual Average Days of the Week and dividing by seven. For short count sites, it is estimated by factoring a short count using seasonal and day-of-week adjustment factors.
- Design hour volume (DHV), K & directional (D) factors, passenger vehicles (PA), and business/commercial vehicles (BC) are calculated from AADT.
- DHV-30: For continuous count (permanent, or perm) stations, this is the 30th-highest hour for the year. For short count (non-perm) stations, this is the highest hour. The accuracy of either of them are dependent on when and how much raw data was collected.
- K%: DHV as a percentage of the AADT.
- D%: Percentage of peak-hour volume (24-hour peak) in the peak direction during that hour.
- PA (FHWA Class 1-3): shown in number of vehicles and percentage of AADT.
- BC (FHWA Class 4 and above): shown in number of vehicles and percentage of AADT.
- The primary federal reporting tool utilized by the Data Collection and Reporting Section is the HPMS. HPMS data is used extensively at the federal level in the analysis of highway system condition and performance.
Helpful Resource Links
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