A head-on collision is one where the front ends of vehicles hit each other, as opposed to a side collision or rear-end collision. This type of accident results in the highest number of fatal crashes because the traveling speeds of both vehicles combine at a high force. For instance, if two vehicles were each traveling at 50 mph and collided the combined speed would equal 100mph.

A head-on crash typically occurs when a vehicle crosses a centerline or a median and crashes into an approaching vehicle, often when passing, but can also be caused by driver inattention. Other times they happen when a driver knowingly or unknowingly travels the wrong way in a traffic lane. 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.

Three- quarters of head-on collisions occur on rural roads or on undivided two-lane roads. This high percentage suggests that many head-on crashes relate to failed passing maneuvers. However roughly 91% of the vehicles involved in fatal head-on crashes on two-lane, divided roadways are related to vehicles either going straight or negotiating a curve.

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. This problem intensifies in the condensed work-zones in the greater Boston area and is expected to increase with the increasing presence of work zones in the future.

The issue of head-on collisions is clearly very complex. An adequate solution to this problem will require more than just providing adequate passing zones.