University of California Institute of Transportation Studies

This report presents a data collection plan for evaluating the greenhouse gas (GHG) impacts of high-occupancy toll (HOT) lane projects implemented under Caltrans' Carbon Reduction Strategy. Because HOT lanes can affect route choice, departure time, vehicle occupancy, and destination choice beyond the managed lane corridor, the report recommends evaluating impacts across the regional travel shed. We recommend two approaches for reliable before-and-after estimates of vehicle miles traveled (VMT) by speed bin. The household-based survey approach uses OBD-II, GPS, or smartphone-based tools to observe a representative sample of households within the travel shed, yielding the most detailed evidence on regional VMT and how impacts vary across the population. The infrastructure-based approach combines continuous freeway sensor data with sampled counts and speeds on arterials, local roads, and ramps; it is less costly and easier to implement but offers less insight into the travelers behind observed changes. For each approach, the report describes what data to collect, where and when to collect it, and how to validate and integrate it with EMFAC. The report also includes order-of-magnitude cost estimates for the two alternatives.