The debate over high-occupancy vehicle (HOV) and high-occupancy toll lane efficiency has raised questions about whether HOVs should be given preferential treatment on managed lanes and the potential impacts of different preferential treatments. This research questions why people choose their mode of travel by examining characteristics of carpoolers and single-occupancy vehicles, reasons for their travel mode choice, and carpool formation, on the basis of a survey of travelers in Dallas-Fort Worth and Houston in Texas. Carpool users rated the ability to use HOV lanes as the most important factor in their decision to form a carpool. Enjoying traveling with others ranked second, followed by reasons such as saving time, helping the environment and society, and sharing vehicle costs. Carpool partner matching programs, employer carpool incentives, and preferred parking at work were generally the least important factors in travelers' consideration of carpooling. The importance of various factors changed significantly if the respondent was on a work or commute trip versus other trip modes. Travelers on work or commute trips ranked travel time savings and cost sharing much higher, as expected, because of their frequent travel during peak hours. The data also support evidence of a significant amount of “fampooling,” with nearly 75% of carpools consisting of family members. The implications of these findings are discussed.

In the last 30 years, determined travelers have developed a new method of travel that offers the benefits of traveling on an HOV lane without forming traditional carpools. Casual carpools, also known as “slugging,” are impromptu carpools formed among strangers to meet the occupancy requirements of HOV lanes. In this research, survey respondent data from Houston, Texas, were used to examine casual carpool passengers. Results of the analyses revealed that being on a commute trip, making more trips per week, being between the ages of 25 and 34, and having professional/managerial or administrative/clerical occupations all increased the likelihood of a traveler choosing to casual carpool. Additionally, having a household income between $25,000 and $35,000 significantly reduced the likelihood of casual carpooling. Understanding the types of travelers who casual carpooled and the information gleaned in these analyses can be used to better evaluate HOV and HOT lane use and performance. Casual carpool passengers can comprise a significant portion of HOV/HOT lane person movement and should be considered when investigating HOV or HOT lane implementation.

Despite the potential of congestion pricing to ease the nation’s ever-increasing congestion problems, there is little quantitative evidence of its ability to spread peak travel demand more efficiently over the course of the day. The objective of the present work is to assess the impact of variable pricing on the temporal distribution of demand to investigate further the role of variable pricing as a travel demand management tool. The Variable Pricing Program of Lee County, Florida, was used as the data source for the study. Because of the limited congestion experienced at the program location, the effects of travel cost changes on the temporal distribution of demand could be isolated. It was found that program implementation had a minimal impact on the overall distribution of demand. Demand for peak-period travel remained relatively unaltered, and active peak spreading was not observed. At the more disaggregate level, however, the impact of the program was more apparent, with significant temporal shifts in the proportion of demand within individual half-hour time segments. Further analysis revealed a price elasticity relationship that was consistent with that in the existing literature. A relationship was also observed between the extent of preprogram peak spreading and the subsequent percent reduction in peak-period travel demand after program implementation. This finding suggests the potential to predict the active peak spreading that may result from congestion pricing. The fact that substantial temporal shifts in travel demand were observed in response to a discount of only 25 cents highlights the potential of variable pricing as a travel demand management tool.