Long-Run Changes in Driver Behavior Due to Variable Tolls

Managing congestion on highways, especially in urban areas, has been a major challenge for transportation planners and researchers. Variable pricing, specifically time-of-day congestion pricing, is one possible method to manage demand and reduce congestion. Because many variable pricing projects are still in the implementation stage, long-run driver responses to variable tolls are largely unknown. Long-run changes are examined in driver behavior in an existing variable pricing project in Lee County, Florida. By using empirical evidence, it was found that over time the relative price elasticity of demand on the Midpoint Memorial Bridge decreased from -0.42 to -0.11 during the early morning discount period. Elasticities have decreased, but to a lesser extent, during late morning and early afternoon discount periods. A discount period volume spreading ratio was developed, and the change in elasticity results was confirmed by using that method of analysis. It was also found that certain characteristics such as frequency of trips, commute trip purpose, full-time employment status, number of people in the household, higher education, and age between 25 and 34 years were all indicators that participants may increase their variable pricing usage over time. Other characteristics, including being retired and having a household income less than $16,000, were indicators that drivers may not increase their variable pricing participation. These results may not be typical for variable pricing facilities. Additional factors, such as the characteristics and influence of any alternate routes, traveler demographics, and size of the toll discount, need to be considered for each project. However, the methodology developed in this research can be applied to other projects to determine those price elasticities of demand and their change over time.