Road collision types

The likelihood of head-on collision is at its greatest on roads with narrow lanes, sharp curves, no separation of lanes of opposing traffic and high volumes of traffic. Crash severity, measured as risk of death and injury, and repair costs to vehicles, increases as speed increases.

Therefore, the roads with the greatest risk of head-on collision are busy single-carriageway roads outside urban areas where speeds are highest.[2]

Contrast this with motorways, which rarely have a high risk of head-on collision in spite of the high speeds involved,[3] because of the median separation treatments such as cable barriers, concrete step barriers, Jersey barriers, metal crash barriers, and wide medians.

The greatest risk reduction in terms of head-on collision comes through the separation of oncoming traffic, also known as median separation or median treatment, which can reduce road collisions in the order of 70%.[4] Indeed, both Ireland and Sweden have undertaken large programmes of safety fencing on 2+1 roads.

Median barriers can be divided into three basic categories: rigid barrier systems, semi-rigid barrier systems, and flexible barrier systems. Rigid barrier systems are made up of concrete and are the most common barrier type in use today[5] (e.g. Jersey barrier or concrete step barrier). They are the most costly to install, but have relatively low life-cycle costs, making them economically viable over time. The second barrier type, semi-rigid, is commonly known as guardrail or guiderail barriers. The initial installation of this type can reach as much as $100,000 per mile.[6] These more forgiving barriers are meant to absorb the impact of a crash, and as a result, increase the cost of their life-cycle with each crash and each repair. The third median barrier type is the flexible barrier systems (e.g. cable barriers). Cable barriers are the most forgiving and the least expensive to install, but have high life-cycle costs due to repair needs after crashes. On the other hand, they have been shown to have calculated cost benefits calculating to as much as $420,000 per mile annually.[5] Much cheaper collision reduction methods are to improve road markings, to reduce speeds and to separate traffic with wide central hatching.[1]

Sealing of safety zones along the side of the road (also known as a hard-shoulder) can also reduce the risk of head-on collisions caused by steering over-correction.[7]

Where a hard shoulder cannot be provided, a "safety edge" can reduce the chances of steering overcorrection. An attachment is added to the paving machine to provide a beveled edge at 30 to 35-degree angle to horizontal, rather than the usual near-vertical edge. This works by reducing the steering angle needed for the tire to climb up the pavement edge. For a vertical edge, the steering angle needed to mount the pavement edge is sharp enough to cause loss of control once the vehicle is back on top of the pavement. If the driver cannot correct this in time, the vehicle may veer into oncoming traffic, or off the opposite side of the road.[8]

From 2008 to 2017, pedestrian deaths resulting from vehicle collisions rose 35%, though areas with Vision Zero initiatives tended to buck this trend.[11]

As of March 2004, the pedestrian traffic fatalities ratio was 11% of all traffic deaths in the US, according to the NHTSA's National Center for Statistics and Analysis.[9] In the US, 14.5% of all deaths on the roads are pedestrians, while this ratio varies from 0.7% in North-Dakota to 45% in the District of Columbia, in 2013; this same year, 0.14 pedestrian per million inhabitant were killed in North-Dakota against 2.70 in Delaware[12]

In cities of over 500,000 inhabitants, the score varied from 6.10 pedestrian deaths per million inhabitants for Detroit (Michigan), to a safer score of 0.85 for Columbus, Ohio, in 2013.[12]

Some well-known fatal collision conditions in the United States include vehicle speed, urban zone, intersection absence and night, according to the NHTSA.[13] According to the GHSA, in the USA, 74% of pedestrian deaths occur at night time, and 72% of the deaths involve pedestrians not crossing at provided road crossing areas.[14]

According to a law professor at the University of South Carolina, if a pedestrian or cyclist is killed in a collision and thereby prevented from providing evidence, there is a risk that they will be unfairly blamed for the collision.[15] At the same time he says that what would lessen those fatalities would be not speeding, not drinking, not texting, and not being distracted.

In the US, in 2013, pedestrian fatalities were higher for the 40+ age group.[12]

The US does not test vehicles for pedestrian safety, and the NHTSA dropped efforts to impose pedestrian safety standards on US automakers more than a decade ago.[9]

Nonetheless, for crosswalk safety, in the US there is not much clarity regarding the need for a crosswalk to be marked or unmarked due to advantages and disadvantages of both approaches, although each city might have its own rules.[17]

In the European Union, 22% of all killed on the roads are pedestrians, while this ratio varies from 11% in the Netherlands to 39% in Latvia and Romania. UK is close to the EU mean with a 23% score. Of all those European pedestrian fatalities, 69% are killed inside urban areas.[18]

In the European Union, 8% of all killed on the roads are cyclists, while this ratio varies from 2% in Greece to 24% in the Netherlands. UK is close to the EU mean with a 9% score. Of all European cyclist fatalities, 57% are killed inside urban areas.[18]

In Europe, the majority of victims were children and elderly persons involving "low-speed" crashes in urban and residential areas.[9]

In France, in 2014, 499 pedestrians have been killed and 4 323 injured. 47% of pedestrians are killed by night (233 pedestrians). This rate is 32% in urban zones, 73% in rural zone (83 death by night) and 91% on motorways (40 death by night).[19]

In Japan, the pedestrian fatality rate is 30% of all road related deaths.[9]

The risk of intersection collisions differs on rural and urban roads, with around 50% of urban crashes and 30% of rural crashes occurring at junctions.[28] In urban areas the likelihood of an intersection collision occurring is high as they typically have a higher density of junctions. On rural roads while the likelihood of a collision may be lower (because of fewer intersections), but the outcome of the collision is often significantly worse because of the increased speeds involved.[29]

Because intersection collisions often result in side-impacts they are therefore often fatal because people are seated close to the part of the car that provides little protection.[2]

Although expensive to implement, roundabouts are an effective way of reducing the speed of traffic at intersections and dramatically reducing the likelihood of high speed right-angle collisions.[30] Clear road markings and signing are low cost methods of improving safety at intersections.[31]