A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Transportation Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2026

Road traffic injuries are a major global issue. In Thailand, fatalities remain high, with a death rate of 25.9 per 100,000 population and about 17,000 deaths per year, of which around 80% involve motorcycle users. One potential approach is the implementation of Non-Exclusive Motorcycle Lanes (NEMCL), which separate motorcycles from mixed traffic. To improve road safety and evaluate the effectiveness of NEMCL, this study examines the impacts on traffic performance and safety. The analysis was conducted using a microsimulation model developed in PTV VISSIM based on data from two study locations, Highway 3414 and Highway 3310 in Nakhon Pathom Province. The model was calibrated and validated using traffic volume and speed data, with the GEH statistic used for traffic volume and the Root Mean Square Error (RMSE) for speed. Safety performance was evaluated using the Surrogate Safety Assessment Model (SSAM). The results show that NEMCL improves traffic safety by reducing conflicts, particularly for motorcycles, but reduces traffic performance, resulting in lower speeds and higher delay and travel time. In addition, lane width has a limited effect under no-overtaking conditions, although wider lanes can improve safety. When overtaking is allowed, wider lanes improve both performance and safety, with a width of 3.5 m providing results closest to the base condition. Access level reduces the effectiveness of NEMCL, as increasing access density lowers both performance and safety due to frequent traffic interruptions. Under two-way operation, changes in lane width have only a small effect on performance, and overall performance is slightly lower than in one-way operation. It also changes conflict patterns, with fewer rear-end conflicts but more head-on conflicts, which represent a higher level of risk. Approaching distance strongly influences safety. Short distances (below 30 m) lead to higher conflict occurrence, while longer distances improve safety, with 200 m providing the lowest number of conflicts. In conclusion, NEMCL can improve motorcycle safety on multilane highways, but its effectiveness depends on appropriate design and operational conditions. These findings can support the development of practical design guidelines for motorcycle lanes in Thailand.