It is customary practice in the United States to base roadway design on the 30th highest hourly volume in a year.Thus, all roadway facilities are expected to operatc at acceptable levels of service for all but 29 hours of the year. The Florida Department of Transportation

(DOT), however, has shifted from the 30th highest hour to the 100th highest hour as the basis for level-of-service determinators. Florida Atlantic University researcher Reid Ewing investigated whether this shift was warranted in the Journal ofSTAR Research (July 1994).The table on page 276 gives the traffic counts at the 30th highest hour and the 100th highest hour of a recent year for 20 randomly selected DOT permanent count stations. MINITAB stem-and-leaf plots for the two variables are provided on p. 278 as well as summary statistics and 95% ~onfidence interval printouts.

a. Describe the population from which the sample data is selected.

h. Does the sample appear to be representative of the population'? Explain.

c. Locate and interpret the 95% confidence interval for the mean traffic count at the 30th highest hour.

d. What assumption is necessary for the confidence interval to be valid? Does it appear to be satisfied?

Explain.

e. Repeat parts c and d for the 100th highest hour.