Vol. 2 No. 1 April 2, 1997

Federal Highway Administration Office of Highway Information Management

Travel Time as a Measure of Customer Mobility and System Performance--

Preliminary Results from NPTS

Travel time is an important measure of mobility for both personal and commercial travelers. States and metropolitan areas frequently measure vehicle travel time on links within their systems to assess effectiveness of congestion management strategies.

National-level travel surveys, such as the Nationwide Personal Transportation Survey (NPTS) and the Census Journey-to-Work, provide the additional opportunity to directly ask users about their travel patterns, including the total travel time experienced for each of their trips. Preliminary 1995 NPTS results give an up-to-date glimpse of travel on our Nation's transportation system. Initial analysis of 1995 NPTS work-trip data allows comparison with the 1980-1990 Census data results. Alan Pisarski reported last year in his publication, Commuting in America, that the Census Journey-to-Work data show average reported commute times across all modes from 1980 to 1990 increased only slightly from 21.7 minutes to 22.4 minutes. Preliminary NPTS data show that from 1990 to 1995, average work times increased only very sightly from 19.6 minutes to 19.9 minutes. (Note: The NPTS shows slightly lower averages because of some differences in survey methodology.) Despite continuing increases in intensity of use and peak congestion on the urban Interstate and other National Highway System (NHS) routes over time, it appears that workers have, on the average, experienced relatively constant travel time to work over the last 15 years or more. Three factors help explain this trend: (1) The continuing shifts to single-occupant personal-vehicle travel to work (a faster mode on average than carpool or transit) over this period is part of the explanation, (2) Shift in commute times out of the traditional peak period, or peak direction is another factor (Travel intensity as reported from HPMS on Urban Interstates over the entire day has shown a steady increase while reported mileage with congested peak-hour travel has been more stable in recent years), (3) The third and very important factor is land use changes and the resulting large increase in suburb-to-suburb work-travel which, on the average, is faster than suburb-to-downtown travel. However, there are likely limits to the ability of travelers to make these shifts in the future. As demand on the system continues to increase, will transportation agencies be able to sustain this travel-time performance into the future? Intelligent Transportation System (ITS) technologies and services are expanding the set of strategies to help achieve that goal.

The full data set for the 1995 NPTS will be available soon and will provide a rich opportunity to provide up-to-date analyses of personal travel patterns for all modes and purposes. Contact Susan Liss at (202) 366-5060 for further information on the NPTS.