|M.Sc Student||Golik Dan|
|Subject||Relationship between Vertical Alignments and Road Accidents|
on Two Lane Highways
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Yoram Shiftan|
|Full Thesis text - in Hebrew|
The geometric design of rural highways, specifically of two-lane highways, has significant impact on their overall characteristics and driving quality. The purpose of this study is to examine the impact of grades of such highway segments, on crash rates and safety.
The data conducted for this study consisted of 4 categories:
1. Crash Data;
2. Traffic Data (Average Daily Traffic);
3. Vertical Grades, and;
4. Horizontal Curvature.
The data was collected for 313 one-kilometer sections of 19 two-lane rural roads in northern and central Israel. Each one-kilometer section was investigated separately for its geometric characteristics including both the average slope and the average curvature on that section.
Accident and traffic data for the period from 2006 to 2009 were obtained from the Central Bureau of Statistics for each of the 313 one-kilometer sections studied. The crash data were divided into two groups:
1. Light crashes; and,
2. Serious and fatal crashes.
For each 1-kilometer section the average horizontal radius is classified into 3 groups, below 300 m., between 300-600 m. and above 600 meters which represented a flat curve.
In order to develop the relationship between crashes and the geometric characteristics and particularly the steepness of the slopes, a Poisson regression approach was adopted.
The results of the analyses conducted for different groups of highway sections demonstrate a minor correlation between vertical alignment and the number of crashes on two-lane rural highways. This tendency remains the same even when horizontal radius is combined.
For example, 2.0 times more serious and fatal accidents are expected when small radius (Rh<300) and moderate grades (g<3%) are combined.
Another finding is that the combination between steep grades and medium radius results less accidents than with small or large radius combined with steep grades.
The decrease in crashes in road sections with steep grades and tight radius can be attributed with the reason that limited sight distance and increase probability of skidding cause slow speeds in addition with the awareness of drivers. On moderate grades and large radius drivers can reach high speed which can cause more accidents.
The results of this study demonstrate that medium radius with the combination of steep grades are preferable when designing at steep grade areas.
Therefore, extra care and special attention to details should be given during the design process of such new roads or improving and upgrading of existing roads.