Traffic engineers are experimenting with two ideas. The first is that erecting signs that say “Accident Reduction Project Area” along freeways will raise awareness and thus reduce accidents. Such signs may have an effect on traffic speed. The second idea is that metering the flow of vehicles onto the on-ramps will spread out the entering traffic and lead to an average increase in speed on the freeway. The engineers conduct an experiment to see how these two ideas affect average traffic speed. First, twenty more-or-less equivalent freeway interchanges are chosen spread well around a single metropolitan area and not too close to each other. Ten of these interchanges are chosen at random to get “Accident Reduction Project Area” signs (in both directions); the other ten receive no signs. Traffic lights are installed on all on-ramps to meter traffic. The traffic lights can be adjusted to require 3 or 6 seconds between entering vehicles. Average traffic speed 6:30-8:30 AM and 4:30-6:30 PM will be measured at each interchange on three consecutive Tuesdays, with our response being the average of morning and evening speeds. At each interchange, the three settings of the traffic lights are assigned at random to the three Tuesdays. The results are in the SAS data program problem1.sas . Analyze the results using the book’s method and using the more traditional split-plot method. Report your conclusions. (Are they the same both ways?)

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