Intersection safety constitutes one of the most critical elements of the highway system in the United States. About 23 percent of fatalities and 49 percent of highway injuries occur at intersections, both signalized and non-signalized. This study will focus on improving safety and operational performances of four-legged crossings by offsetting them and creating two offset T-intersections. Conclusions and recommendations: (1) If angle collisions are abnormally high, one of the most economical remedies is to provide separator islands on the minor approaches; (2) A deflection of the entry path will force minor-road drivers to slow down and become more responsive to their environment. This treatment is most effective in rural areas for 2x2- and 2x4-lane intersections; (3) For 2x2-lane TWSC rural intersections, the application of offset T-intersections is a treatment option to improve safety at high hazard locations. Derived benefits apply to both perpendicular and skewed crossings; (3) On an aggregate level, the expected benefit of converting a cross intersection to an offset T-intersection is a reduction in total crashes of 20 to 30 percent for rural 2x2-lane TWSC intersections. A reduction in fatal/injury crashes is expected to be approximately 40 per cent; (4) According to the trend shown in figure 6, at flows greater than 10,000 entering ADT with a 10 per cent traffic flow on the minor road, a conversion to offset T-intersections may not be cost-effective. At higher flows, warrants 1 or 2 for signal installation are likely to be met; (5) For 2x4-lane TWSC intersections in rural areas, converting a cross intersection to an offset T-intersection is a viable option that is expected to reduce crashes considerably at low to medium flows up to about 25,000 ADT. Similarly, the warrant for installing signals is likely to be met at the upper limits. Nevertheless, a single-volume warrant may not always be a satisfactory reason for signalization. The expected reduction in total crashes ranges from about 60 to 40 percent for divided four-lane highways with design speeds greater than 80 km/h (50 mi/h); and (6) In urban environments, a high hazard or congested 2x2-lane signalized intersection could benefit from a conversion to two offset T-intersections in safety and traffic operations when the design is L-R only. The derived advantages are an expected 20 per cent reduction in total crashes at higher ADTs and 5 to 20 s/veh less travel time. In tight urban environments, this conversion is possible in a grid network by closing some access and/or rerouting traffic. A future research topic is to determine guidelines on the offsets between two signalized T-intersections with 2x2-lane and 2x4-lane intersections. (A) For the covering abstract of the conference see ITRD no 207828. The reprints are also available at the web - http://www.vti.se/pdf/reports/K18APart1.pdf; http://www.vti.se/pdf/reports/K18APart2.pdf and http://www.vti.se/pdf/reports/K18APart3.pdf.
Abstract