The Highway Department monitors traffic accidents for a one-year period along a stretch of limited access highway. The interchanges on the highway are one of two designs (A or B). Table 13.18 gives...

The Highway Department monitors traffic accidents for a one-year period along a stretch of limited access highway. The interchanges on the highway are one of two designs (A or B). Table 13.18 gives the number of crashes for each interchange during the year. The interchanges vary in their volume of traffic, so the data set also includes the estimated average weekly traffic load (AWTL, in 1000s of vehicles) at each interchange. Is there evidence that the two designs differ in their safety? If so, say which design appears to be less safe, and estimate the impact on the rate of crashes. (Hint: assume that AWTL does not affect the rate of crashes.)