Traffic Counts

Traffic Counts for County Roads


Last updated January 5, 2023

Why Pierce County Counts Traffic

Pierce County uses electronic traffic data recorders to collect daily traffic counts on most arterial roads. Traffic counts are conducted on a regular basis, and are primarily used to monitor roadway use and changes in traffic flow. Counts are also used for planning improvements throughout the road system.

Annual Average Daily Traffic (AADT)

The AADT is the total volume of traffic on a segment of road for one year divided by the number of days in the year. We generally set up traffic counters for 24 to 48 hours and then use day and month adjustment factors to give an estimate of the AADT.

Most arterials are counted every one to two years. There are more than 10 locations in the county where we collect traffic count data 24 hours per day, all year long.

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