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Section VII
National Household Travel Survey (NHTS)

The National Household Travel Survey (NHTS) is the only source of national statistics and trend data on the travel of the American public by all modes of transportation. In addition to broad indicators of use such as mode share, overall trip rates, vehicle occupancy rates, travel time and distance, and trip purpose distributions, the NHTS provides detailed data on the characteristics of travelers, trips, and vehicles. The 2001 NHTS is the most recent in the series of these national travel surveys. Previously known as the Nationwide Personal Transportation Survey (NPTS), NHTS data is also available for 1969, 1977, 1983, 1990, and 1995.

The 2001 NHTS is a rich source of information about travelers and their characteristics, household composition, the amount and type of trips that people take every day, and selected information about household vehicles. The data include characteristics of all household trips, by all modes, and all purposes.

RESEARCH METHODOLOGY

The Federal Highway Administration conducts the National Household Travel Survey (NHTS) approximately every five years. As a sample survey, the target population for the 2001 NHTS was U.S. residents (of all ages) living in households. The study utilized a Random Digit Dialing (RDD) list-assisted sample, yielding interviews from 176,000 people living in 67,000 households throughout the United States. Each household received a pre-contact letter with incentive to participate, followed by a telephone recruitment interview. Each participating household then received a travel-diary for recording trip-making details. The information stored in the diary was then retrieved using Computer Assisted Telephone Interviews (CATI). Information collected in the diary included all trips for all purposes for all modes on an assigned day for all people in the household. The survey also collected long-distance trips (over 50 miles from home) for the four weeks prior to the interview date.

OVERVIEW

The NHTS collects data on all trips taken by household members during an assigned travel day. Detailed information is collected on household and person demographics, characteristics of household vehicles and trips, and contextual data on worker characteristics, residential location, and estimates of annual driving. As a comprehensive, intermodal research program the NHTS series provide data to:

GROWTH IN TRAVEL, 1969 - 2001

From 1969 to 2001, the U.S. has experienced a level of growth in travel demand that far exceeds population growth. As an aging population, the number of people 65 and older in the U.S. has grown by over 68 percent since 1969. In comparison, the number of persons under 16 in the U.S. grew by a rate of 7.5 percent. Overall, the U.S. population has grown by 40.6 percent since 1969 (Table NT-1).

While there were modest increases in the population and the number of households over the past 30 years, the U.S. experienced dramatic increases in all four measures of travel: person trips, person miles of travel (PMT), vehicle trips and vehicle miles of travel (VMT). NT-1 and NT-2 show the enormous increases in travel demand (169 percent increase in vehicle trips) at a time when the number of the roads in the highway system has remained relatively the same. Since 1969, the number of additional road miles in the U.S. has increased by only 6 percent. 

According to the NHTS there is nearly one vehicle (0.97) for every person 16 years and older in the U.S. In fact, over 25 percent of U.S. households now have three or more vehicles. More importantly, vehicle use has also increased. Since 1969, the average annual vehicle miles generated by American households has increased from 12,423 to 21,187, a 59 percent increase. Overall VMT has grown 194 percent.

Many factors have contributed to the explosive growth in travel on our highways, including the population surge of the baby boomers, high levels of immigration, increases in the number of households, increased rates of vehicle use by older drives, and the continued dispersion of work, home, and recreation locations.

It is significant to note that during the same time period annual number of fatalities on our nation’s highways decreased by 20 percent--from 50,000 to 40,000 traffic fatalities per year. In terms of air quality, the air we breathe is actually cleaner than it was in 1969. There was a 43 percent decrease in carbon monoxide, a 59 percent decrease in volatile organic compounds (VOC), and a 5 percent increase in nitrous oxide (NOx) (NT-2).

OFF-PEAK CONGESTION

Congestion is typically thought of as a commute to work phenomena that occurs during morning and evening peak periods. However, the NHTS shows that the highway system is carrying more shopping, errands, and social/recreational travel at all times of the day. Although weekday travel continues to see very high usage peaks during the morning and evening rush hours, weekend and mid-day travel demand has heightened to commute peak levels.

NT-3 shows a time of day travel comparison for a typical weekday (Wednesday) and weekend (Saturday). Midday travel (between noon and 3.pm.) rivals morning congestion levels. Saturday at 1:00 p.m. has a higher number of vehicle trips than either the morning or afternoon peak periods on a typical weekday. Friday afternoon is still the highest travel period, because of the overlap of work-related, social, and recreational trip purposes.

COMPLEXITY OF COMMUTING TO WORK

The phenomenon of trip chaining—linking a series of short trips (stops of 30 minutes or less, such as to stop at a store or to drop kids at school or day care) into the commute to or from work complicates our understanding of the typical journey to work. Census Journey to Work data does not include actual travel characteristics and details of the commute trip such as regular stops during travel to work. The stops and the way to and from primary destinations (such as work locations) have an impact on key travel indicators including departure time, travel time, and route choice.

Commute trips are often thought to be highly repetitious, and therefore, highly predictable. In actuality, commute trips vary in length and time by day and direction, and trip chaining impacts commuters’ departure time, route choice behavior, and miles traveled to work.

Table NT-4 shows that in 2001, nearly 19 million weekday workers (27 percent of all weekday workers) chained trips as part of their commute compared to 17.3 million in 1995 (25 percent of weekday workers). Over 1.5 million more weekday workers made short stops during their commutes in 2001 than in 1995—almost all of them added stops in the home-to-work direction of the trip which had a 21 percent increase, while the people who chained trips in both directions increased by over 12 percent.

URBAN AND RURAL TRAVEL BEHAVIOR

There are significant differences in the travel of people who live in rural areas compared to those who reside in urban areas. Rural households have more vehicles and are more likely to have older vehicles, especially pick-up trucks. The average age of a vehicle in a rural household is 8.7 years compared to 7.9 years for an urban vehicle. Rural households account for more vehicle miles of travel, each rural resident on average drives 3,100 miles more per year, or 25 percent more than their urban counterparts.

As shown in Chart NT-5, rural residents travel longer distances for all trip purposes. The most significant disparity is for work trips. Rural residents have an average work trip length of 14.0 miles while urban commutes average only 10.6 miles.

HOUSEHOLD VEHICLE FLEET

Over half of the U.S. private-vehicle fleet is comprised of passenger cars (Table NT-6). Within the household vehicle fleet, pick-up trucks have the greatest average age at 9.1 years. The vehicles with the lowest average age are Sports Utility Vehicles (SUVs) at 5.6 years. This is in part due to the recent introduction of SUVs to the market. Household cars have an average age of 8.0 year and accrue the fewest annual miles per vehicle. SUVs and pick-ups are both driven more than cars with average annual VMT of 14,091 and 12,522, respectively.

Having the lowest fuel economy at 16.7 mpg, SUVs are 12.5 percent of all personal vehicles and account for 14.1 percent of all household-based VMT. Pick-ups also have low fuel economy (16.9 mpg) and make up 18.2 percent of the household-based fleet, accounting for 19.5 percent of all household-based VMT.

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