الفهرس 
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Abstract
The main objective of this research is to evaluate the risk related to geometric design features
for horizontal curves by using reliability analysis. In this approach, the variables in the design
equations are treated as random variables, which are expressed as probability distributions rather than deterministic values as vehicle’s speed and side friction. This research focuses on the large radius of horizontal curves (from 700 to 2000 m) that most of previous researches
were for small radius. Appropriate design of geometric elements in roads is an important feature for safety measures, The stopping sight distance (SSD) and the radius (R) of the horizontal curve are the most
important geometric elements at the horizontal curve section. Both SSD and R increase with increase in speed. However, the available sight distance (ASD) at site can be regulated by
varying R and middle ordinate (M) at the curve section. This study focuses on the intercity rural freeways roads in Egypt. Traffic and geometry data were collected for 9 curves from 3
freeway roads that connect between the cities. All roads have posted speed limit of 100 to 120 km/h, Horizontal curves were selected to cover the different geometric characteristics like
(middle ordinate, radius, super elevation, deflection angle, lane width and shoulder width) and traffic data like Spot speeds. Reliability analysis by Minitab program focuses on two modes of noncompliance in horizontal curve design according to mean operating speed(V mean) and 85th operating speed percentile(V85). The first mode of noncompliance occurs when the required
horizontal curve radius (R demand) exceeds the available horizontal curve radius (Ravilable).The second mode is insufficient sight distance which means that available sight distance (ASD) on
the horizontal curve is less than required stopping sight distance (SSD). The results showed that all curves satisfy the demand radius by users which have reliability equal 100%,
In the other hand probability of non-compliance is calculated to evaluate the stopping sight distance , where non-compliance occurs whenever the available sight distance (ASD; supply)
falls short of the stopping sight distance (SSD; demand). Then, the contributions of uncertainty in the geometric variables were evaluated. The results showed that about approximate 50% of studied curves has reliability values exceed 90%, and other the reliability values were between 75 to 90 % according to V85. The statically analysis was performed to obtain the minimum level of safety of AASHTO
design value for middle ordinate (M), and showed that AASHTO design values were between 90 to 95 % of level of safety. Comparison between trucks and passenger cars is applied according to evaluation of horizontal curve radius under V85.