KOTI - Korea Transport institute

Road speed limits are to set the maximum speed of vehicles on roadways. As the speed limit is closely related to driver’s driving behavior, this has been disputed among drivers for decades. For example, people might say that the speed limit is too low even though the width of road is enough to drive fast, or some say that the speed limit is too high while the road is narrow. These are drivers’ desires from a subjective point of view, but it implies that speed limits need to be decided by taking road features such as road width, number of lanes, traffic volume, the proportion of heavy vehicles, and land-use into consideration. In other words, there is a demand for reasonable speed limits.

Speed limits in the Republic of Korea (hereafter ‘Korea’) are regulated by Korea’s Road Traffic Act and the speed limits have been widely set at 60 km/h for most urban roads and a speed limit equal or higher than 80 km/h has been allowed for two-lane roads. However, this speed limit regulation is limited to comprehensively consider the surroundings of roads such as land-use, population, and the proportion of heavy vehicles, which define the functionality of roads. Ultimately, this limitation in law hinders the decisions for reasonable speed limits. In addition, the national police agency in Korea recently announced that the speed limits for urban roads will be lowered to 50 km/h or 30 km/h (called ‘speed limit changes 5030’), based on the claim that the speed limits of urban roads in Korea are higher than many of those in Europe and North America.
With this background in mind, this study investigated the effectiveness of speed limit changes for urban roads in terms of safety (i.e., accidents) and mobility (i.e., travel speed and time). The study results indicated that lowering speed limits decreases accidents and mitigates the severity of accidents. Although the lowering of speed limits slightly increased travel time, it did not make a large impact as travel times on urban roads are significantly affected by traffic signals. With this in mind, lowering speed limits will carry a positive impact for urban roads, based on the fact that the accident reduction impact (benefit) is greater than the travel time increases impact. This finding justifies the speed limit changes policy in Korea. In addition, this study suggested that road characteristic indexes be considered when setting speed limits for urban roads, and also proposed a reasonable procedure for determining speed limits. These study results will help to set reasonable speed limits, and we hope that this study enhances traffic safety onurban roads.