1. Continuous counts are taken 365 days a year at a small number of locations. These counts provide a variety of useful information. Because these counts are most consistent and are maintained at permanent locations, the FHWA summarizes the information in a monthly Travel Volume Trends (TVT) report.

2. Control or seasonal counts are much more difficult to characterize because different State planning organizations perform these counts differently. These counts are usually taken from two to twelve times a year, for periods of time ranging from 24 hours to two weeks. The main purpose of control counts was to help identify traffic patterns on specific roads in order to help place those roads into seasonal adjustment factor groups. Control counts can also be used to compute highly accurate measures of annual average daily traffic at specific locations, and are very effective in high growth or recreational areas. The 1985 version of the Traffic Monitoring Guide (TMG) did not utilize control counts for the development of grouping procedures or for AADT estimation.

3. Coverage counts are short duration counts, ranging from six hours to seven days, distributed throughout the system to provide point-specific information and area-wide coverage. Coverage count programs also vary considerably, as the diverse requirements and constraints faced by State highway agencies have translated into divergent programs. Many States have implemented coverage programs that feature relatively long (2 to 7 days) traffic counts, but where only a part of the State is counted every year. Other States have emphasized complete coverage of the highway systems each year, resulting in a large number of short duration (usually 24 or 48-hour) counts.