Crashes and Effective Safety Factors within Interchanges and Ramps on Urban Freeways and Highways

The aim of this study is to analyze effective factors crash in safety that occurs in influence areas of freeway ramps. The data for this research has been collected from freeway interchanges in central of an ABC highway (to protect the actual company name). The collected data of five crashes which had occurred in black spot interchange ramps was analyzed using SPSS statistical package version 18.0 (USA) and Microsoft office Excel 2007. According to AASHTO, ramp design speeds should approximate the low volume running speeds on intersecting highways. Where this design speed is not practical, ramps should not be designed at less than 50 percent of the design guideline for freeway and expressway ramps, where only those values of highway design speed above 80 km/h apply. Chi-Square Test was used to statically analyze the distribution of crashes according to their causes. However, chi square value of 135.75 (α<0.01) has indicated that a high percentage (79.17%) of crashes which were examined, were caused by over speeding followed by, loss of control, sleepy driver, bumper to bumper, loss of wheel, bad driving behaviour, hit and run with percentages, 8.33, 4.17, 4.17, 4.17, 2.08, 2.08 respectively. The result of the crash data analysis showed 50 types of accidents. A large percentage of crashes were caused by over speeding, in term 76% of severity with damage only, for type of collision 94% of crashes out of control. About 88.60% of crashes happened at daytime and 57.80% in fine weather conditions. It has been noticed that the distribution of crash among different condition of weather are equally shared, however, it was found out that weather, statistically, is not a strong factor in crashes. Ramps are scheduled for auditing based on descending road speed limits.