solution

Traffic sign maintenance. Refer to the Journal of Transportation Engineering (June 2013) study of traffic sign maintenance, Exercise 8.54 (p. 489). Recall that civil engineers estimated the proportion of traffic signs maintained by the North Carolina Department of Transportation (NCDOT) that fail minimum retroreflectivity requirements. The researchers were also interested in the proportions of NCDOT signs with background colors white (regulatory signs), yellow (warning/caution), red (stop/yield/wrong way), and green (guide/information). In a random sample of 1,000 road signs maintained by the NCDOT, 373 were white, 447 were yellow, 88 were green, and 92 were red. Suppose that NCDOT stores new signs in a warehouse for use as replacement signs; of these, 35% are white, 45% are yellow, 10% are green, and 10% are red. Does the distribution of background colors for all road signs maintained by NCDOT match the color distribution of signs in the warehouse? Test using a = .05.

Exercise 8.54

Exercise 8.54

Traffic sign maintenance. The Federal Highway Administration (FHWA) recently issued new guidelines for maintaining and replacing traffic signs. Civil engineers at North Carolina State University conducted a study of the effectiveness of various sign maintenance practices developed to adhere to the new guidelines and published the results in the Journal of Transportation Engineering (June 2013). One portion of the study focused on the proportion of traffic signs that fail the minimum FHWA retroreflectivity requirements. Of 1,000 signs maintained by the North Carolina Department of Transportation (NCDOT), 512 were deemed failures. Of 1,000 signs maintained by county-owned roads in North Carolina, 328 were deemed failures. Conduct a test of hypothesis to determine whether the true proportions of traffic signs that fail the minimum FHWA retroreflectivity requirements differ depending on whether the signs are maintained by the NCDOT or by the county. Test using  = .05.