1995 NPTS Databook - National Household Travel Survey - Oak ...

INTRODUCTIONtelephones may result in an under-count oflower income households. Data from the1990 Census indicate that 4.7 percent ofU.S. households do not have telephones,and those households are largely found inthe South and West.• The 1990 and 1995 surveys allowedanother household member (proxy) toreport an individual’s trips if the individual(14 and older) could not be contacted afterseveral attempts, while the earlier surveysdid not allow such proxy interviews. Thistype of proxy interviews, which occurred inapproximately 18 percent of the cases inthe 1995 survey, may contribute to agreater number of trips being reported thanin earlier surveys.• In the 1969 survey, “vehicles” wereautomobiles, station wagons, and passengervans. In later surveys, vehicles alsoincluded pickup trucks, other light trucks,sport utility vehicles, motorcycles, andmopeds. Footnotes have been addedthroughout this publication to remindreaders of this difference.• The 1990 and 1995 survey data wereedited by CATI during the data collectionprocess, while data from the earlier surveyswere edited manually after the interview.The advantage of CATI over conventionalhome interviews is that many datainconsistencies and data quality problemscan be immediately identified andcorrected.• The sample size of the surveys variedconsiderably: 15,000 households for the1969 survey, 18,000 for 1977, 6,500 for1983, 22,000 for 1990, and 42,000 for1995. The small sample size in the 1983survey (less than one-third that of 1990)contributed to a larger sampling error.The following changes, taken from the User’sGuide, apply only to the 1995 NPTS:• Two odometer readings and the associateddate of the readings, planned to be takentwo to six months apart, were attemptedfor each household vehicle. A model toestimate annual miles driven from these tworeadings and other information wasdeveloped. The odometer readings werecollected and annualized to produce aseparate estimate of vehicle miles of travel(VMT), in addition to the owner’s estimateand the summation of travel day trips madein that vehicle.• The first three surveys were conducted bythe U.S. Census Bureau using an areahousehold sample in 1969, 1977, and1983. However, because the CensusBureau had conducted the survey, therewere very strict confidentiality requirementsand neither the address nor the Censustract could be identified outside the Bureau.For the 1990 NPTS, FHWA chose not tocollect address information. It was notnecessary to do so because the survey wasconducted totally by phone with no diarymailings. Home and work addresses werecollected in the 1995 NPTS. The purposeof collecting the addresses in 1995 was tomail the travel diaries, and also to addadditional geographic detail to the data files.However, addresses are not part of thedataset. A series of characteristics of thearea of the residence and workplacelocations was appended to the data files toallow analyses of the landuse–transportation connection.• For the first time in the NPTS series, the1995 survey contained questions on the1-4NATIONWIDE PERSONAL TRANSPORTATION SURVEY