A Master of Science thesis in Civil Engineering by Mohammad Essam Alozn entitled, “Estimating the Impact of Combined Horizontal and Vertical Curves on Drivers’ Perception”, submitted in November 2019. Thesis advisor is Dr. Akmal Abdelfatah. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).
Highway design focuses on providing safe facilities and smooth mobility on road networks. The increasing rate in highway accidents’ fatalities resulted in an increasing demand for evaluating and improving highway design methodologies. Dubai road safety is a major concern as per its Roads and Transport Authority’s (RTA) vision to have a safe and smooth transport for road users. Among the most critical highway segments that affect safety are the ones that include combined horizontal and vertical alignments. The driver’s perception is highly affected due to the existence of combined curves. This research aims at developing a procedure for the evaluation of the effect of combined horizontal and vertical curves on drivers’ perception. Several combined curves’ scenarios are developed to highlight the impact of curve combination on driver’s perception. The proposed three-dimensional curve scenarios were created through importing their horizontal and vertical alignments to a computer animation software to extract their driving perspective views. These views were presented to a sample population to record their perception. A hypothesis stating that all drivers perceive horizontal curve radius with the right perception, in the presence of combined horizontal and vertical curves, is tested to examine if the combined curves have an impact on the drivers’ perception. The collected data show no significant statistical difference among drivers’ groups regarding age, nationality, and combined curves type groups. Based on the collected data, a regression model was developed to predict the deviation from the right perception percentage of the horizontal curve radius when it is combined with a vertical curve. The statistical analysis performed with (α=5%) showed that several geometric parameters affect drivers’ perception of combined curves with different rates. The consistency model examines the drivers’ behavior on combined curves. The model was applied to road segments with combined alignments to evaluate them. Also, the developed methodology was compared with other consistency models developed in other countries. Finally, the developed model proves that there is a misperception of the horizontal radius while driving on a combined curve. The research provides some recommendations to avoid the negative effects of the drivers’ misperception of the road dimensions.