University of California Transportation Center

The valuation of travel time savings has been an important theme in transportation research because it is the single largest contributor to the benefits of many transportation projects. It also plays a central role in deciding about the size and scope of public investment and has important welfare implications. It can shed important light as to whether any congestion pricing scheme will have increase social welfare or not. And help us understand how commuters make their travel decisions. The San Diego I-15 Congestion Pricing Project (SDCPP) is a demonstration project where an existing High Occupancy Vehicle lane has converted to HOT (High Occupancy/Toll) lane. Beginning in 1996 these lanes were made available to solo drivers who pay a toll. The toll adjusts every six minutes to maintain free flowing traffic on the HOT lane. Carpoolers get to use the lane for free as before. This presents us with a unique opportunity to study commuters’ choice between a tolled and a free alternative based on not only what the commuters say they would do (SP), but also on what they actually did (RP).

The general result is that this tolled facility is used by high income, middle aged, homeowners, female commuters. An interesting result that comes out of this analysis is the dual effects of toll. If the actual toll rises above the mean toll then the commuter is more likely to take the FasTrak lane. Another interesting implication that the effect of toll is conditional on the level of uncertainty of travel time and conversely uncertainty in travel time encourages use of FasTrak lane only if toll rises above a threshold value. Commuters are more sensitive to variations in travel time in the morning, specially during the peak, than in the afternoon.

Another salient result is that the Value of Time estimates from Stated Preference models are significantly lower than the Revealed Preference estimates. The difference is consistent and persistent across the different models which lead to the conclusion that these differences are real. Probably it reflects the difference in responses of individuals to actual and hypothetical situations.