Interchange Sight Distance and Design: Aspects and Implementation

The primary purpose of an interchange is to enable an appropriate level of access to the freeway in a safe and beneficial way to the driver. It improves road safety and traffic operation by reducing or eliminating traffic conflicts that would occur if grade separation were not provided (e.g. intersection). Crossing conflicts are eliminated and turning conflicts are either eliminated or minimized. The paper focuses on sight distance criteria in the geometric design of interchanges and junctions, specifically, implementation of stopping sight distance (SSD) and decision sight distance (DSD). These issues incorporate implementation of sight distance policy for: ramps’ geometric design, ramp terminals’ components, and basic lanes’ reduction. These sight distance criteria can alleviate safety by reducing conflicts and confusion to the driver and by keeping alignment simple, direct, and consistent. Specifically, DSD affects traffic control and intelligent transportation systems applications.