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Setting safe speed limit is very critical and complex phenomenon, which has to be decided based on the road hierarchy that categorizes roads according to their functions and capacities, and poses certain restrictions in the design process. However, this is challenging in urban regions of developing countries, where rapid city growth forces high-speed intercity roads to serve as urban arterials, along which traditional 50 km/h limit is not practically possible. To lower the speed variation (and provide mobility), speed limit increase is allowed as high as 82 km/h as in the case of urban arterials in Turkey. To understand the real impact of such controversial countermeasures, which is the main scope of this study, spatiotemporal distribution of accident hotspots along urban arterials are analyzed in GIS using nearest neighbor hierarchical (NNH) clustering; changes between 3 years before and after periods are evaluated using as hit rate (HR), predictive accuracy index (PAI), and recapture rate index (RRI) indices. For a case study of 7 urban arterials in Ankara, NNH analysis (with nmin= 5 and dmax= 250 m) resulted in 94 clusters in the before period, while there were 101 clusters in the after period; and decreased PAI values in the after case showed more accidents in the clusters, demonstrated no real improvement by speed limit increase. Application of safe system approach in the critical hotspots also showed that speed limit increase on the study corridors in Ankara was against the safe limits suggested by UNECE based on possibility of certain accident types. [ABSTRACT FROM AUTHOR]

A geographic information system (GIS) is a commonly used method for analyzing traffic accidents. Through a GIS, data regarding traffic accidents can be presented visually, and traffic accident locations can be analyzed. By identifying locations where traffic accidents frequently occur and highway sections with high accident rates, traffic authorities can adopt preventive measures and enforce traffic regulations to reduce the frequency of traffic accidents, deaths, injuries, and financial losses. The present study analyzed tourist traffic accidents in Nantou County, one of the most popular tourist areas in Taiwan for domestic and international travelers, and tabulated statistical data that were subsequently input into a GIS database to determine dangerous locations and areas where traffic accidents are prone to occur. First, administrative regions in Nantou County were identified and kernel density estimation and repeatability analysis were performed to determine locations with high accident rates. The results showed that in Nantou County, traffic accidents often occur between 12:00 and 18:00 at intersections and on sloped roads and windy roads. The most dangerous locations were Provincial Highway 21 (areas around Sun Moon Lake) and Provincial Highway 14A (areas with access to Qingjing and Hehuanshan). The results of this study could serve as a reference for traffic authorities to develop measures for preventing and regulating traffic accidents. [ABSTRACT FROM AUTHOR]