As the improvement of air quality has become increasingly critical to the SCAG region, the ability of SCAG to accurately predict the impacts of transportation improvements and air quality mitigation measures has become more important. Accurate air quality analysis requires accurate predictions of both traffic volumes and traffic speeds. Travel demand models, like the one employed by SCAG, have typically focused on predicting demand accurately, not speed. Speed has traditionally been an input that demand modelers adjusted as necessary to improve the accuracy of the volumes forecasted by the model. Consequently federal and state regulatory agencies have shown an increasing interest in the validation of both the volume estimates and the speed estimates produced by demand models. The project objectives of the Arterial Speed Studies are listed below:
1) The primary objective of the first Speed Study was to test various low cost data collection techniques for measuring speeds against the “floating cars” method. By collecting speed and other data simultaneously at a pilot test location, different methods of speed estimation can be compared and calibrated to determine the most accurate and cost effective methods available for more widespread use across the SCAG region.
2) Building the comprehensive database of measured speeds and volumes needed for developing new volume delay functions, validating model speeds, and tracking speed changes over time.
3) Develop and test new volume delay functions for both arterials and freeways.