OPTIMAL SAMPLE SIZE OF ROADSIDE-INTERVIEW ORIGIN-DESTINATION SURVEYS
The objective of the study reported herein was to establish an optimal sample size for roadside-interview origin-destination (O-D) surveys for various conditions and to investigate the cost-effectiveness of O-D surveys and means to improve it. Three representative survey locations were selected: a major intercity and international route, a busy intercity route with commuter traffic, and a rural highway with local agricultural traffic. The study examines the effect of variables such as sample size, sampling technique, survey location, and trip purpose on sampling error for trips involving personal vehicles. It appears that the theoretical sampling errors provide a good estimate of the magnitude and probable distribution of observed sampling errors and may be used for the selection of field sampling rates to achieve a desired survey accuracy. The significance of sampling errors was evaluated in view of the magnitudes of other errors common in the transportation planning process. Fifty percent bidirectional sampling over a 12-hour period is recommended for models used mainly as predictors of future traffic patterns. On the other hand, five to ten percent bidirectional interviewing is probably sufficient if the model objective is mainly educational, permitting decision-makers to appreciate the complex relationships between transportation and land use and the probable consequences of alternative policies. The cost-effectiveness of roadside-interview O-D surveys was evaluated by calculating the marginal costs of improving the total inventory phase error by making improvements in sampling error and factoring error. In general, it appears that the extension of the 12-hour survey period is usually more cost effective than an increase in sampling rate during the 12-hour period.
Ontario Ministry of Transportation & Communic, CanResearch and Development Division, 1201 Wilson Avenue
Downsview, ONo M3M 1J8, Canada
- Hajek, J J
- Publication Date: 1977-1
- Features: Figures; References; Tables;
- Pagination: 20 p.
- TRT Terms: Commuters; Cost effectiveness; Data collection; Intercity travel; International compacts; Interviewing; Mathematical models; Origin and destination; Roadside; Rural highways; Sampling; Surveys
- Uncontrolled Terms: Models
- Subject Areas: Highways; Operations and Traffic Management; Passenger Transportation;
- Accession Number: 00157282
- Record Type: Publication
- Report/Paper Numbers: RR 208
- Files: TRIS
- Created Date: Nov 23 1977 12:00AM