Segment characteristics and severity of head-on crashes on two-lane rural highways in Maine

Abstract

More than two out of three of all fatal crashes in Maine occur on rural, two-lane collector or arterial roads. Head-on crashes on these roads account for less than 5% of the crashes, but they are responsible for almost half of all fatalities. Data analyzed in this study was provided by Maine Department of Transportation and covers all head-on crashes for 2000–2002 during which period there were 3136 head-on crashes reported. Out of these, 127 were fatal crashes and 235 produced incapacitating but not fatal injuries. These two categories made up over 75% of the crash cost. A clear majority of head-on crashes on two-lane, rural roads in Maine were caused by drivers making errors or misjudging situations. Illegal/unsafe speed was a factor in 32% of the crashes while driver inattention/distraction was a primary factor in 28%. Fatigue was responsible for around one in 40 crashes and one in 12 fatal crashes. Alcohol or drugs was a factor in one in 12 crashes and one in nine fatal head-on crashes. Less than 8% of fatalities involved someone overtaking another vehicle, and only around 14% involved a driver intentionally crossing the centerline. Two in three fatal head-on crashes occurred on straight segments and 67% of these happened on dry pavement. There is a clear trend towards higher speed limits leading to a higher percentage of crashes becoming fatal or having incapacitating injuries. There is also a clear trend – if one keeps speeds constant and AADT within a certain range – that wider shoulders give higher crash severities. Also, for higher-speed roads, more travel lanes (than two) increase crash severity. In summary, there seems to be two major reasons why people get across the centerline and have head-on collisions: (a) people are going too fast for the roadway conditions; or (b) people are inattentive and get across the centerline more or less without noticing it. The latter category of crashes could probably be reduced if centerline rumble-strips were installed. More or less all head-on collisions could be eliminated if median barriers were installed. In-vehicle technology could also be used to significantly reduce the incidence of lane departures. Furthermore, today's speed limits should be better enforced since a high percentage of serious crashes involve illegal speeding. This should be combined with lowered speed limits for targeted high-crash segments.

Introduction

About 60% of all fatal crashes in OECD Member countries happen on rural roads (OECD, 1999) and as much as 80% of these crashes fall into three categories: single vehicle crashes (35%), head-on collisions (25%), and collisions at intersections (20%) (Wegman, 2003).

Two-lane rural highways make up a substantial proportion of the highway network in northeastern United States as in most of the world. In the state of Maine, roughly 95% of all rural highway miles are only two lanes wide. Furthermore, as the population continues to spread outside established urbanized areas as a result of population sprawl, traffic volumes on these facilities are increasing. This is expected to lead to an increased number of crashes involving vehicles traveling in opposite directions. A disturbing finding since Fig. 1 shows that head-on crashes in the late 1990s already accounted for almost half of all traffic fatalities on non-interstate rural roads in Maine even though less than 5% of all crashes there were of head-on type.

Fatal crashes will be a focus of this paper since they are responsible for about half of the crash costs when it comes to head-on collisions—as shown later in this paper. Therefore, an analysis of a small number of crashes illuminates the causation of roughly half the crash cost. Also, fatal crashes are reported to a higher degree than other ones, are the ones that are the most thoroughly investigated with respect to cause, have the most reliable data, and are the ones that easiest can be found in data banks.

Rural, non-interstate crashes, the ones presented in Fig. 1, make up a clear majority of the fatal crashes in the state of Maine. The Fatality Analysis Reporting System (FARS) web-based encyclopedia (NCSA & NHTSA, 2005) shows that there in 2002 were 186 fatal crashes in Maine involving 272 vehicles. Fourteen (8%) of the fatal crashes occurred on rural interstate highways, 58 (31%) on other rural arterials, 55 (30%) on rural collector roads, 38 (20%) on rural local roads, and 4 on rural roads with unknown classification. There were two crashes with unknown urban/rural designation. This means that over 90% (169–171 out of 186) of the fatal crashes in the state were rural and less than 10% (15–17) occurred in urban compact areas. The fact that more than two out of three (127–133 out of 186) of all fatal crashes in Maine occurred on rural collectors/arterials means that this is where a considerable part of the safety improvement efforts ought to be concentrated. And, head-on collisions are the ones taking roughly half of all lives on these roads. Clearly, something should be done to reduce the number of head-on collisions. An obvious first step is to identify what is causing these head-on crashes – especially the fatal ones – and do whatever is necessary to reduce their occurrence, or at least their severity.

Research into what factors are correlated with head-on-crash occurrence indicates that the frequency of head-on crashes decreases with increased lane width (Al-Senan and Wright, 1987, Zegeer et al., 1981) and that most fatal head-on crashes take place on roadways with high posted speed limits (Al-Senan and Wright, 1987, Leisch, 1971) and at passing zones (Agent and Deen, 1975). Also, the vehicle crash severity is affected by speed limit (Renski et al., 1999), road width (Huang et al., 2002), and segment curvatures (Abdel-Aty, 2003). A study from New Zealand (Clissold, 1976) found that head-on collisions were over-represented in wet weather on both urban and rural roads. An analysis of 505 fatal head-on crashes in Minnesota (Minnesota Department of Transportation, 2004) shows that almost 50% (243 of 505) of the crashes were attributed to “driving left of roadway center—not passing,” which typically would indicate inattention, while 109 (22%) were classified as “illegal or unsafe speed,” 95 (19%) as “other human contributing factor,” 90 (18%) as “driver inattention or distraction,” and 73 (14%) as “improper or unsafe lane use.” Only 59 (12%) were classified as skidding and 57 (11%) as weather related in spite of Minnesota's northerly climate with long, snowy winters.

A comprehensive overview using national data on head-on collisions is provided by NCHRP (2003). Results from that study is presented later in this paper as comparison material to Maine results.