# Impact of Lowering Speed Limit on Urban Transportation Network
## 2 Literature Review
### Studies on the Effect of Lowering the Speed Limit  
[PERSON] and [PERSON] evaluated the effect of lowering speed limit in urban areas targeting a total of 29 sections conducted by the Busan Metropolitan Police Agency from 2010 to 2015. As a result of analyzing traffic accident statistics for 1 to 3 years before and after lowering speed limit, the number of traffic accidents decreased by only 3.09% and the number of injuries by only 8.76%, but the number of fatalities decreased by 36.73%, indicating high effectiveness of lowering speed limit in reducing fatalities. In addition, an average travel speed of 6.31 km/h was reduced after lowering speed limit. In most areas, there were statistically significant reductions in average travel speed, confirming the effectiveness of the lowering speed limit policy [8].  
[PERSON] compared travel speed, number of traffic accidents, and number of fatalities in the Seoul metropolitan area. The study showed that by lowering speed limit, traffic accidents on provincial roads decreased [9].  
[PERSON] analyzed the effect of lowering speed limit on travel speed and traffic accidents before and after the speed limit change. After lowering speed limit, it was confirmed that the travel speed decreased, and the number of traffic accidents decreased as well [10].  
[PERSON] evaluated the lowering of speed limit through comparative analysis of the average speed and speed deviation before and after implementing speed limit lowering policy [11]. The results showed that the effect of the policy implementation on average travel speed and standard deviation varied by locations [12; 13]. The findings of the previous research are summarized in Table 1.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Authors** & **Findings after Lowering Speed Limit** \\ \hline [PERSON] and [PERSON] (2018) & Average 6.31 km/h decrease \\ [PERSON] (2020) & 4.9\% (urban roads) and 4.6\% (rural roads) of speed decrease \\ [PERSON] (2007) & Reduction in traffic volume, speed, and traffic accidents \\ [PERSON] (2020) & Reduction in average speed \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of previous research.  
Studies on Effects of Speed Limit Reduction or Speed Management Measures on Transport Network or Driver Behavior  
[PERSON] and [PERSON] conducted an in-depth study of the behavior of drivers negotiating horizontal curves before and after realignment. They found that the path radius could be different from the curve radius, due to substantial variations in lateral placement as vehicles approach and traverse the curves. The study results also showed that contrary to earlier studies, there was not a strong relationship between speed and path radius, but the friction demand does tend to increase as speed increases [14].  
[PERSON] and [PERSON] examined the speed profiles of individual vehicles on traffic-calmed streets, in order to provide a better understanding of how drivers react to calming devices over an extended street length and to find ways of estimating speeds along traffic-calmed streets. The results indicated that traffic-calmed streets did not necessarily promote low-speed environments. It was found that 85 th percentile speeds at long distances from calming devices were 45-55 km/h for horizontally deflected streets and 40-45 km/h for vertically deflected streets. The study found that drivers had different perceptions of appropriate operating speeds. Also, it was concluded that the most significant factor in determining speeds on streets with vertical deflections was the spacing between devices and the spacing of devices from the street entry [15; 16; 17].  
[PERSON] and [PERSON] investigated the effect of roadway widths for street narrowing with a particular focus on speed and yielding behavior. A 6 m wide two-way pinch-point was found to be not effective in slowing most private vehicles down. The study found that drivers travelled at a similar speed whether they were crossing the pinch-point by themselves or with opposing traffic approaching [18].