Date

2019-06-20

Author

Türe Kibar, Funda
Tüydeş Yaman, Hediye

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Turkey, as one of the middle-income countries, is facing with an increasing motorization in the last decades. This situation also causes a major traffic safety problem on Turkish roads, where 7000+ people lost their lives, and almost 300,000 people get injured annually. When considering factors causing traffic accidents, ‘speed’ is a complex phenomenon which needs to be examined with more attention and different dimensions. This becomes even more problematic in urban regions that face large migration and thus, experience growth in not only built area size. The latter also results in major changes in the road hierarchy, as former high capacity intercity mobility corridors are transformed into urban arterials with legal speed limits of 50 km/hr. As a correction to this mismatch between the high capacity and low speed limits of major urban arterials in Turkey, Traffic Coordination Centers (TCCs) are given the right to change speed limits up to (+/-32 km/hr), provided that necessary measures taken. It is observed that “necessary measures” were not listed clearly in a legislation, nor are they ever discussed scientifically before decision making, as shown in this paper. To detect the main challenges in safe urban speed management, this paper first focuses on the concept of safe urban speed limits with support from literature, safe system approach (SSA) proposed by United Nations Economic Commission for Europe (UNECE) and Turkish legislation. In the second part, numerical evaluation of traffic safety problems along an urban corridor before and after speed limit change in Ankara is presented. The accident hotspots were determined using Nearest Neighborhood Hierarchical (NNH) clustering technique in Geographic Information Systems (GIS) environment. In the clustering process, accidents associated with speed were selected covering 3-year periods before and after the speed limit change were studied using a minimum of 5 accidents and maximum distances of 125m and 250m as required parameters in NNH. The results showed that traffic safety problems which existed in the before situation, remained the same, if not increased, after the speed limit increase, which is an indication of lack of necessary precautions. Furthermore, loss/lack of road hierarchy was detected as one of the main reasons contributing to traffic safety problems which allowed pedestrians to be exposed to high speed motorized traffic as well as sideswipes along the urban corridors.

URI

http://www.icearc2019.com/
https://hdl.handle.net/11511/73575

Collections

Department of Civil Engineering, Conference / Seminar