Final Report: Investigation of Traffic Count Procedures on Unpaved Roads

About the report:

This report inventoried the current costs and procedures of VDOT's Secondary Count Program, with special attention to costs and procedures for traffic counts on unpaved roads. A survey of VDOT's nine District Traffic Engineers on unpaved road counts, a field evaluation of the accuracy of road tubes on unpaved roads, results of a literature review on alternative procedures for obtaining traffic volumes on unpaved roads, and a survey of the other states that maintain a system of secondary roads, are presented. Of the 9,931 secondary road counts requested in 1993, 2,143 were on unpaved roads. Cost estimates indicated that counting unpaved roads was approximately 17% of the secondary count program expenditure in 1993. The actual field work constituted approximately 10% of the expenditure; the remaining 90% was office work and support services. The District Traffic Engineers were concerned about the accuracy of unpaved road counts, due to local residents tampering with the equipment and the need to apply adjustment factors to the raw counts. Field evaluation of the road tubes indicated that they performed well on unpaved surfaces. However, the programmable counters were more accurate on unpaved roads than the cumulative models currently used by the Department. The literature review indicated that mechanical traffic counts are the most cost-effective way to collect traffic volumes. Trip generation and traffic forecasting methods have no inherent accuracy. Most other states responsible for maintaining a secondary road system do not have specific programs or guidelines for counting unpaved roads, but all of these states use road tubes. Programmable counters can produce hourly counts and provide machine-readable data, which would help identify false counts resulting from tampering with the equipment, reveal possible equipment failures during the counting period, relieve VDOT staff of having to retrieve counters from the field after precisely 24 hours, and reduce the risk of recorder error by downloading the counter directly to a computer. Based on the literature reviews, inventories, surveys, and field tests, all traffic counts on unpaved roads should use programmable, machine-readable counting devices.

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