COMPUTATIONAL RESEARCH PROGRESS IN APPLIED SCIENCE & ENGINEERING (CRPASE) CRPASE: TRANSACTIONS OF CIVIL AND ENVIRONMENTAL ENGINEERING Journal homepage: http://www.crpase.com CRPASE: Transactions of Civil and Environmental Engineering 8 Article ID: 2227, 1–7, Special Issue: NCTT 2021 ISSN 2423-4591 Research Article Understanding the Factors Affecting Urban Vehicle-to-Vehicle Crash Severity with Focus on Drivers' Route Familiarity Mahyar Vahedi Saheli  Department of Civil Engineering, Faculty of Engineering, University of Guilan, Rasht, Iran Keywords Abstract Urban crash severity, Vehicle-to-vehicle accidents, Unfamiliar drivers, Familiar drivers, Route familiarity. Human factors are usually of paramount importance when it comes to traffic crashes. Drivers' route familiarity or unfamiliarity is a critical human-related factor that has less been considered in the literature. This factor can lead to inattention, distraction, and dangerous behaviors due to familiar drivers' over-confidence or unfamiliar drivers' insufficient knowledge of road geometry and environment. The main objective of this study is to discover the factors affecting the severity of vehicle-to-vehicle crashes in Rasht city (in northern Iran) involving unfamiliar and familiar drivers using a logistic regression model. The results indicate the significant effect of human factors such as driver's familiarity and age, collision type, angle and reason, temporal factors (season and time of day), vehicles involved in the crash, and environmental conditions on the injury severity of vehicle-to- vehicle crashes in urban roads. The results of this study can be used by policymakers and implementers to take appropriate measures to reduce the severity of vehicle-to-vehicle crashes in urban areas. 1. Introduction Traffic crashes are a leading cause of injury and death in many countries worldwide. Iran is one of the developing countries with high rates of traffic-related injuries and deaths. The proportion of traffic injuries in Iran is higher than in most other parts of the middle-east and the rest of the world. Road traffic crashes are also one of the country's most serious problems and among the top five leading causes of death in Iran [1]. The five categories of contributing factors to traffic collisions are human, vehicle, road, environment, and traffic [2, 3]. Research has shown that human factors play a significant role in about 90% of crashes [4]. Among all human-related crash variables, one of the most frequent driver-related critical errors is driver distraction [4-7]. The issue of driver distraction can be closely linked to the drivers'  Corresponding Author: Mahyar Vahedi Saheli E-mail address: mahyarvahedi@msc.guilan.ac.ir Received: 16 November 2021; Revised: 18 December 2021; Accepted: 17 January 2022 https://doi.org/10.52547/crpase.8.2227 Academic Editor: Mahdi Feizbahr Please cite this article as: M. Vahedi Saheli, Understanding the Factors Affecting Urban Vehicle-to-Vehicle Crash Severity with Focus on Drivers' Route Familiarity, Computational Research Progress in Applied Science & Engineering, CRPASE: Transactions of Civil and Environmental Engineering 8 (2022) 1–7, Article ID: 2227. route familiarity, which however is less considered in the literature. A route familiar driver travels on a route well-known from long or close association, and traveling on that specific route made up of various road features has been the stimulus frequently encountered [8]. Both familiarity and unfamiliarity with roads may have adverse effects on driving tasks. High route familiarity can cause driving distraction and overconfident driving behaviors like overspeed driving to reduce the travel time [9]. On the other hand, high route unfamiliarity may lead to driving errors due to unfamiliar road features [10]. At first glance, unfamiliar drivers may seem safer than familiars since their attentional capacity is strongly focused on collecting information related to the road environment. Therefore, because the road is not well-known, they should be less likely to be distracted and less prone to speeding and risk-taking behaviors [9]. Yet, this good