Relationships between safety and congestion were developed in Phase II of Project L07 for application in the spreadsheet-based analysis tool, which evaluates the effectiveness of alternative design treatments for non-recurrent congestion. The safety/congestion relationship was initially developed from analyses of traffic operational and crash data for the freeway systems of two metropolitan areas: Seattle and Minneapolis-St. Paul. The data for these two metropolitan areas generally showed a U-shaped relationship with the lowest crash rates in the middle of the crash rate range at about LOS C. The research in Task IV-5 evaluated traffic operational and crash data from Sacramento, California, and both the Kansas and Missouri portions of the Kansas City metropolitan area to determine whether a similar U-shaped relationship between safety and congestion exists for the freeway systems of these metropolitan areas as well. A combined safety-congestion relationship was developed from data for the freeway systems of three metropolitan areas: Seattle, Minneapolis-St. Paul, and Sacramento. The combined relationship showed a similar U-shaped relationship and suggests that design treatments that are effective in reducing congestion levels on urban freeways should also be effective in reducing crashes. (Author/publisher)
Samenvatting