Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-018-3610-7 RESEARCH ARTICLE - CIVIL ENGINEERING Modeling Geometric Design Consistency and Road Safety for Two-Lane Rural Highways in the West Bank, Palestine Khaled Al-Sahili 1 · Mohammed Dwaikat 1 Received: 19 June 2018 / Accepted: 21 October 2018 © King Fahd University of Petroleum & Minerals 2018 Abstract This study investigates the effect of geometric design consistency on road safety in the West Bank. Studies have shown that operating speed, vehicle stability, alignment indices, and driver’s workload are the common consistency measures that might affect safety. A total of 118-km two-lane rural highways in the West Bank, Palestine, were studied based on limitations of available data. Comprehensive geometric and operating data for the selected highways obtained from field survey, maps, and official sources were used to investigate the effect of design consistency measures on road safety. Crashes for years 2008– 2012, totaling 263, were used for model development using the generalized linear regression approach. Tested models were statistically significant at 95%, and adopted models showed acceptable levels of goodness of fit. The recommended model performed well across additional highway sections, additional years of data, validation of algorithm, and “%error” with a high linear correlation. The study adds to the evidence that several geometric design consistency measures contribute to roadway safety. The significant measures for the two-lane rural highways in the West Bank were segment length, traffic volume, difference between operating and design speeds, absolute difference in the 85th percentile speeds between successive design elements, and the ratio of individual curve radius to the average radius. The practical implication of this study, in addition to being able to predict crashes based on the recommended measures, highway designers should pay careful attention to inconsistent designs of two-lane rural highways to reduce their crash frequency. Keywords Design consistency · Two-lane rural highway · Consistency model · Palestine 1 Introduction and Background The primary goal of a transportation system is to provide safe and efficient movement of people and goods. Traffic crashes represent a concern to all members of society; therefore, it is important to reduce these crashes and their severity. One of the tools to improve roadway safety is to assess the consis- tency of the design and its impact on road safety. Design consistency means how much highway geom- etry conforms to driver’s expectancy and how much the roadway’s physical elements conform to standards and con- straints. “Collisions tend to be more frequent in locations where a sudden change in road character violates the driver’s expectations. The concept of design consistency addresses this by comparing adjacent road segments and identifying B Khaled Al-Sahili alsahili@najah.edu 1 Civil Engineering Department, An-Najah National University, Nablus, West Bank, Palestine sites with changes the driver might find sudden or unex- pected” [1]. Therefore, it is important for designers to make sure that roadway geometry is consistent with driver’s expec- tations. The primary inputs to the driving task are roadway geom- etry, traffic conditions, and roadside environment. These are used to determine the workload requirements on the driver. The ability of drivers to handle these inputs depends on their expectancy and other human factors. Castro and Santos- Berbel [2] showed that design consistency (based on vehicle speed) and available sight distance (based on visibility) could be related to crashes in approximately 4% of cases. Several researches in this field focused on the impact of roadway geometric characteristics, rather than geometric design consistencies, on road safety. There is no universally clear definition of inadequate design since more than one factor might contribute to this. Designers generally address these issues; however, much work is still needed in this field. Furthermore, the contribution of design consistency mea- sures to road safety might vary from one location to another 123