Investigation of Traffic Safety Effects of Speed Limit Increases in Main Arterials

2018-09-30
Türe Kibar, Funda
Tüydeş Yaman, Hediye
Setting safe speed limits requires consideration of different factors (operating speeds, road hierarchy, etc.), especially in urban corridors. With a legislative change, speed limits were increased from 50 km/hr by 32 km/hr on some urban arterials in Turkey, effect of which is examined for Ankara urban arterials in this study. Shifts in traffic accident hotspots, which were determined using Nearest Neighborhood Hierarchical (NNH) Clustering in Geographical Information System (GIS) environment, are quantified using three different indices as Hit Rate (HR), Predictive Accuracy Index (PAI) and Recapture Rate Index (RRI). The 3-year before and after cases included 1533 accidents and 1687 accidents, respectively. NNH with minimum accident number, n min =5, and maximum distance, d max = 100 m, produced 88 clusters covering 900 accidents (HR=58.71%) for the before case, while it detected 93 clusters with 926 accidents (HR= 54.89%) for after case. While higher d max values increased cluster numbers slightly, d max =500 m produced fewer clusters in both cases, as more accident data were associated in a cluster with high distance tolerance. Though there was a slight decrease in fatality statistics after the increase, a slight increase in number of hotspots and accidents suggests that i) the operating speeds were already high before, ii) the traffic safety along the corridors did not improve much, though it may ease enforcement of the corridors, iii) it increased the dispersion of accident locations decreasing HR values (not desired, as it may endanger effectiveness of traffic safety countermeasures).
13th International Congress on Advances in Civil Engineering, ACE2018 (12 - 14 Eylül 2018)

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Citation Formats
F. Türe Kibar and H. Tüydeş Yaman, “Investigation of Traffic Safety Effects of Speed Limit Increases in Main Arterials,” presented at the 13th International Congress on Advances in Civil Engineering, ACE2018 (12 - 14 Eylül 2018), Çeşme, İzmir, Türkiye, 2018, Accessed: 00, 2021. [Online]. Available: https://www.ace2018.net/.