Head-On Collisions

Type of Problem Being Addressed

General Description of the Problem

The 1999 FARS statistics 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. Both studies concluded that these types of passing crashes were not considered a significant problem (Alexander and Pisano, 1992; Mohamedshah, 1992).

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 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 an ROR crash can become a head-on crash if the vehicle "overrecovers" into the opposing travel lane.

Specific Attributes of the Problem

Conventional wisdom suggests that it would be highway curves rather than tangents that would present drivers with particular negotiating problems. Vehicles would be expected to cross the centerline more frequently on curves. However, as shown in Exhibit III-1, the majority of head-on fatalities on all roads and on two-lane rural roads are on tangent sections. For all roads, 33 percent of the 1999 head-on fatal crashes were on curves and 67 percent on tangents. For two-lane rural roads, the percentage on curves increased to 37 percent. These results most likely reflect the fact that the largest proportion of road sections is tangent. However, it is clear that both tangents and curves have significant problems and warrant treatment. Therefore, specific strategies are suggested for both curved and tangent sections in this guide.


EXHIBIT III-1
Percentage of Head-On Fatal Crashes for Curves and Tangents for Two Categories of Road Exhibit III-1