Head-On Collisions

Executive Summary

Introduction

This emphasis area addresses head-on crashes associated with highway (i.e., nonintersection) segments. A head-on crash typically occurs when a vehicle crosses a centerline or a median and crashes into an approaching vehicle. A head-on crash can also occur when a driver knowingly or unknowingly travels the wrong way in a traffic lane. Head-on crashes occur as a result of a driver's inadvertent actions—as with run-off-road (ROR) encroachments—or deliberate actions—e.g., executing a passing maneuver on a two-lane road.

Statement of the Problem

The 1999 statistics from the Fatal Analysis Reporting System (FARS) indicate that 18 percent of noninterchange, nonjunction fatal crashes were two vehicles colliding head-on. The percentage was the same for 1997 and 1998 data. In addition, these data reveal that

• 75 percent of head-on crashes occur on rural roads,
• 75 percent of head-on crashes occur on undivided two-lane roads, and
• 83 percent of two-lane undivided road crashes occur on rural roads.

The high percentage of head-on crashes on rural, undivided, two-lane roads might suggest that many head-on crashes relate to failed passing maneuvers. However, in nearly all cases, fatal head-on crashes occur in nonpassing situations. Of 7,430 vehicles involved in head-on crashes on two-lane, undivided roadway segments, only 4.2 percent involved a vehicle "passing or overtaking another vehicle" (1999 data). The corresponding percentage for rural roads was 4.3 percent. These low fatal-crash percentages are corroborated by two studies performed by the Federal Highway Administration's (FHWA's) Highway Safety Information System (HSIS). According to the studies, all crashes either were passing related or occurred in no-passing zones.

This does not imply that passing crashes should be excluded from a fatality-reducing program, just that strategies should likely be chosen to reflect that roughly 91 percent of the vehicles involved in fatal head-on crashes on two-lane, divided roadways are related to vehicles either "going straight" (68 percent of the total head-on fatalities) or "negotiating a curve" (23 percent of the total). Comparable percentages hold for the rural roads.

It might also be expected that a significant proportion of head-on collisions occur in construction zones—locations where the traffic pattern is altered and opposing lanes may be brought closer together than normal. However, FARS data indicate that in 1999 only 1.9 percent of noninterchange, nonjunction head-on crashes (90 of 4,713) occurred in construction zones. While this problem could intensify with an increasing presence of work zones in the future, it is clear that programs aimed at reducing fatalities in head-on collisions should concentrate on "normal" highway sections.

These statistics indicate that most head-on crashes are likely to result from a motorist making an "unintentional" maneuver—the driver falls asleep, is distracted, or travels too fast in a curve. There may be other contributing factors, such as alcohol use or speeding.

Given these factors, affecting head-on fatalities is clearly more complex (and perhaps more difficult) than just providing adequate passing zones. Indeed, most head-on crashes are similar to ROR crashes—in both cases, the vehicle strays from its travel lane. In cases involving unintentional maneuvers, the causes are likely to be very similar. Potential head-on crashes can become ROR crashes if there is no oncoming vehicle, and a ROR crash can become a head-on crash if the vehicle "overrecovers" into the opposing travel lane.

Programs and Strategies

Objectives

The objectives for reducing the number of head-on fatal crashes are to

• Keep vehicles from encroaching into the opposite lane,
• Minimize the likelihood of a car crashing into an oncoming vehicle, and
• Reduce the severity of crashes that occur.

These objectives are similar to those cited for ROR crashes (emphasis area 15.1; see Volume 6 of this report, the ROR guide). The objective of reducing the severity of crashes is covered under the ROR emphasis area.

For each objective identified (except for the third objective, which is discussed in Volume 6 of this report, the ROR guide), there exist various strategies (Exhibit I-1). Each strategy is described in detail in this guide. Strategies may fall into either of two categories—treatments implemented over extended sections of highway or treatments at selected spot locations.

Exhibit I-1
Objectives and Strategies for Addressing Head-On Crashes

Objectives	Strategies
18.1 A—Keep vehicles from encroaching into opposite lane	18.1 A1—Install centerline rumble strips for two-lane roads 18.1 A2—Install profiled thermoplastic strips for centerlines 18.1 A3—Provide wider cross sections on two-lane roads 18.1 A4—Provide center two-way left-turn lanes for four- and two-lane roads 18.1 A5—Reallocate total two-lane roadway width (lane and shoulder) to include a narrow "buffer median"
18.1 B—Minimize the likelihood of crashing into an oncoming vehicle	18.1 B1—Use alternating passing lanes or four-lane sections at key locations 18.1 B2—Install median barriers for narrow-width medians on multilane roads

Other Head-On Strategies

Other head-on strategies that are also ROR ones include the following (they are discussed in Volume 6 of this report, the ROR guide):

• Enhanced delineation of sharp curves;
• Improved highway geometry, especially for horizontal curves, including design elements such as curvature, superelevation, and widening through the curve;
• Better pavement markings;
• Skid-resistant pavement surfaces;
• Improved shoulders to prevent ROR overrecovery, including paving, eliminating edge drops, and improving shoulder slopes; and
• Rumble strips to slow vehicles on approaches to hazardous locations.

Another approach to addressing safety problems in a comprehensive way is to replace the independent activities of engineers, law enforcement personnel, educators, judges, and other highway safety specialists with cooperative efforts, an approach reiterated in these guides.