The AAA Foundation for Traffic Safety is dedicated to saving lives through research and education. Fundamental to the research that we perform is the ability to quantify traffic risks. Quantifying traffic risks requires data regarding not only the motor vehicle crashes that occur and the number of people who are involved, injured, and killed in crashes, but also data regarding to people’s exposure to risk, such as the number of miles that they travel. A great deal of important research can be performed using aggregate data regarding the number of miles travelled by vehicles in the transportation system, which are collected routinely by state governments and published annually by the United States Federal Highway Administration (FHWA). However, many important research questions require data regarding exposure to risk that in relation the characteristics of individual travellers, such as their age, their sex, and the type of vehicle that they are driving. Such data are collected on the national level in a large survey conducted by the FHWA. This survey, called the National Household Travel Survey (NHTS) (and previously, Nationwide Personal Transportation Survey [NPTS]), has been essential to some of the most important traffic safety studies of the past two decades including a study by the AAA Foundation which quantified the relative risk that older versus younger drivers pose to other people, 1 as well as the seminal study of the relationship between the presence of passengers and a teenage driver’s risk of being involved in a fatal crash. 2 While the data from the NHTS has been an integral part of numerous studies, researchers’ ability to rely on the NHTS to monitor trends in traffic safety is limited by the fact that the NHTS is conducted only periodically and at irregular intervals. For example, the most recent NHTS was conducted from March 2008 through May 2009. Statistics from the National Highway Traffic Safety Administration show that the annual number of police-reported crashes decreased by 2.1% between 20083 and 2013 4, and the annual number of people killed in crashes decreased by 12.6%, whereas the FHWA’s aggregate statistics derived from counts of vehicles indicate that total vehicle miles of travel increased by 0.4% over the same period. 5 Without data relating driving mileage to the characteristics of drivers, vehicles, and trips, a clear understanding of the mechanisms by which these declines in crashes and fatalities have come about has eluded researchers. To address the need for current data regarding driving exposure in relation to driver, vehicle, and trip characteristics, the AAA Foundation has commissioned a team of researchers at the Urban Institute to perform a survey to develop, pilot test, and implement a data collection system to collect these data at the national level on an ongoing basis, with a special focus on young drivers and senior drivers–two long-term priority areas for AAA Foundation research. That data collection system–the American Driving Survey–was launched on May 21, 2013 and is presently ongoing. The statistical methods and survey instrument for the American Driving Survey (ADS) were developed by the Urban Institute in collaboration with the AAA Foundation. The sample of the ADS comprises United States residents ages 16 and older who live in a house with landline telephone service and/or have a cellular telephone and can be interviewed in either English or Spanish. ADS data are collected via telephone interviews by Social Science Research Solutions (SSRS). In ADS interviews, a household member aged 16 years or older is selected at random and is asked to report information about all of the trips that they made during a 24-hour period that began in the morning of the day before the interview. Teenage drivers, drivers ages 75 and older, and drivers who reported driving “almost every day” are oversampled. The ADS interview is designed to collect data that is essential for future research envisioned by the AAA Foundation, and to collect it cost-effectively and with minimal respondent burden. The ADS does not seek to replicate the design, structure, sample, or data of the FHWA’s NHTS. This report documents the methodology of the ADS as well as the results of the first full year of data collection, which occurred between May 21, 2013 and May 31, 2014. Interviews were conducted with 3,319 drivers sampled from among 4,287 households that were initially contacted and screened. The first year data show that all drivers 16 and older drive, on average, 29.2 miles per day or 10,658 miles a year. Men reported driving more miles than women; Caucasians reported driving more miles than respondents of other races; Hispanic respondents reported driving the least. Teenagers and drivers ages 75+ also drive significantly fewer miles on average. About one-third of all drivers did not drive at all on the day about which they were interviewed. About 50% of all miles driven are in a car, and another 40% in an SUV or pickup truck. People drive, on average, more on weekdays and less on weekends. There is a significant mileage gap between rural and urban drivers, but the gap is smaller on the weekends than on weekdays. People drive, on average, less during the winter months and more during the summer months. While the scope and content of the ADS differs from the FHWA’s NHTS in many important ways, our estimates of miles driven in light vehicles, overall and in relation to driver characteristics, are quite similar to comparable results in the 2009 NHTS. Notable exceptions include young drivers, older drivers, and women, who reported more driving in the ADS than in the NHTS, whereas drivers ages 35-54 reported less driving in the ADS than in the 2009 NHTS. The extent to which any differences reflect errors in either survey, legitimate differences in the scope of the two surveys, or changes in travel from the data collection period of the NHTS (2008-2009) to that of the ADS (2013-2014) is unclear. These findings are described at greater length in the major sections that follow. The first section below briefly summarizes our research approach and methods. The second major section of the report focuses on the number, length, and duration of driving trips categorized by key socio-demographic variables such as sex, age, educational attainment, and residential and regional location. This section includes a preliminary comparison of our initial estimates to the 2009 NHTS. The third major section includes information on the type of vehicle driven by respondents and whether they drive alone or with passengers. The fourth major section of the report focuses on seasonal and daily variations in driving behaviour. The fifth section of the report describes the number of drivers and vehicles in the households interviewed. The sixth section describes the driving behaviour of teenage drivers and those 75 and older. The seventh section is a detailed description of all aspects of the sampling methods and survey instrument and survey protocols. (Author/publisher)
Samenvatting