Impacts of Traffic Signal Control Strategies

The LHOVRA is the predominant isolated signal control strategy in Sweden. Past-end green was originally incorporated as part of LHOVRA (the O function) and was intended to reduce the number of vehicles in the dilemma zone. Coordinated signal control in Sweden is often fixed-time with local vehicle actuated signal timing adjustments and bus priority. The aim was to evaluate the following strategies using Stockholm as a case study: 1. The LHOVRA technique with a focus on the O function; 2. Fixed time coordination (FTC); 3. Fixed time coordination with local signal timing adjustment (FTC-LTA); 4. FTC-LTA as above + active bus priority (PRIBUSS); 5. Self-optimizing control (SPOT). Field measurements were used for study of driver behavior and traffic impacts. VISSIM & HUTSIM simulation models calibrated and validated with empirical data were used to study traffic performance and safety impacts of the suggested improvements. TRANSYT was used to produce optimized signal timings. A method to calculate the approach delay was developed based on the observed number of queuing vehicles at the start and end of green.