Tim Lomax

Developing a Total Peak Period Travel Time Performance Measure

Transportation performance measures based on travel time quantities satisfy a range of mobility purposes. The measures can show the effect of many transportation and land use solutions, and they are relatively easy to communicate to a range of audiences. The concept of total travel time has been discussed since the early 1950s, but because of data inaccessibility, the planning community has rarely used total travel time as a measure. For the initial implementation of the total peak period travel time measure in the Urban Mobility Report, data from the reports primary data sets were combined in a new way to estimate road users’ total travel time during the peak period. Data shortcomings were addressed with simplifying assumptions to create a calculation method that would offer a more refined value than would the use of raw or incomplete data. Total peak period travel time can provide additional explanatory power to a set of mobility performance measures and bridge the gap between traditional delay-based measurement and accessibility.

Estimating the Effect of Operational Improvements in the Houston Area

Measuring the effects of transportation system improvements has long been a challenge. Two estimates—the congestion index method and the travel delay method—are used to produce a range of possible benefits resulting from the implementation of transportation projects and programs. The congestion index method uses the roadway congestion index (RCI), and its relationship with congestion cost per capita, to estimate the benefit derived from operational improvements. The RCI provides an areawide assessment of congestion based on freeway and principal arterial street system daily vehicle kilometers of travel per lane kilometer data. The travel delay method calculates congestion cost by associating the value of time, cost of fuel, and cost of operating commercial vehicles with travel delay estimates. These two methods are used to estimate the effects of three types of transportation system improvement projects/programs—freeway traffic management system, high-occupancy vehicle lanes, and regional computerized tra...