Sample size determination for spot-speed studies at rural intermediate, and urban locations.

In the estimation of traffic characteristics by a sampling technique, the design of experiment requires the determination of an adequate and economical sample size. The evaluation of speed characteristics is accomplished by a sampling survey and a statistical analysis. A statistical procedure previously developed for sample size determination made possible the design of a spot-speed study with a sample size that is statistically acceptable. The measure of speed variability can be obtained from the results of previous speed surveys. However, a reliable estimate of standard deviations permits the use of the equation for determining sample size. The findings of the previous investigation were supplemented by analyzing these standard deviations of spot-speeds for 2-and 4-lane highways in rural, intermediate and urban areas. References' applied general statistics, 2nd edition, f. E. Croxton and d.j. cowden, prentice-hall 1955. Sample size requirements for vehicular speed studies, j.c. oppenlander, w.f. bunte and p.l. kadakia, hrb bull. 281, pp 68-86, 1961. Traffic characteristics on illinois highways, illinois division of highways, 1961.