During the problem identification phase of the program, a number of criteria were considered when identifying the sites. First, using the most current Washington data (2002), 10-mile segments of the interstates were ranked in terms of the number of crashes that involved CMVs, the average daily traffic, the proportion of CMVs included in the daily traffic where available, existing enforcement citations for aggressive driving, and various combinations of truck and passenger vehicle crashes. State roads were also considered.
Further criteria considered in site selection were the cost of the media markets in the intervention corridors and the possible media spillover into a comparison corridor, corridors where enforcement could use aircraft assistance and where shoulders were wide enough to make a safe traffic stop. Finally, road conditions, such as the number of lanes, areas where trucks were not permitted in the left lane, and planned construction projects were considered. From a list of the top ten locations, the final intervention and comparison sites were selected.
As shown in Figure 7, the two intervention corridors were I-5 south of the City of Tumwater (Thurston County) to the SR-512 exchange south of the City of Tacoma (Pierce County) and I-5 from the City of Stanwood through the southern part of the City of Bellingham (Skagit and Whatcom Counties). The two control/comparison corridors were on I-5 from the City of Kalama through the vicinity of State Route 506 (Kelso) and I-90 just west of the City of Spokane to the vicinity of the Maple Street exit in the City of Spokane.