#40 Collisions With Roadside Objects

Previous briefs in the Road Solutions series have looked at barrier treatments, clear zones, and motorcycle underrun protection. These treatments are all designed to minimise the impacts of crashes involving departure from the roadway, which may be caused by a range of driver- and road-related factors. This week, we look closer at single-vehicle run-off-road (SVROR) collisions and the injury outcomes relative to different collision partners (including no collision). Generally, road safety barriers are installed in the knowledge that collision with a barrier is likely to be less severe than the event that would occur in the absence of a barrier. Specific hazardous collision partners most commonly include trees, poles, kerbs, bridge piers, signs, walls, buildings and embankments.

With a large amount of research published on this general topic, detailed findings of specific studies vary and there are many different methods and variables applied. In this case, we focus on a relatively recent study by Albuquerque and Awadalla[1], which analysed 555 SVROR injury crashes in Abu Dhabi where a driver was the sole vehicle occupant. Of all crashes included in the study, 12% resulted in driver fatality.

Relative risk

The most harmful objects struck in around 80% of cases were trees, poles, barriers and kerbs. Crashes involving W-beam and concrete barriers were frequent and accounted for 31% of all crashes, and 9.7% of these crashes were fatal. However, crashes involving trees and poles combined accounted for a similar number of crashes, but these were fatal in 15.6% and 16.2% of cases for trees and poles, respectively.

Table 1: Roadside object crashes and severity (source: Albuquerque, 2020)

Considering relative odds of fatality, collisions with trees, poles and concrete barriers were calculated to be 3.1, 4.7 and 2.5 times higher, respectively, compared with W-beam guardrail crashes. It was noted that impacted poles were generally located closer to the road than impacted trees, and that “no signs or poles were equipped with breakaway devices or any other form of energy-absorbing mechanism”, which may help to explain some of the differences in odds of fatality. Further, while barriers generally showed the best safety performance, they also “presented a less-than-desirable performance in terms of vehicle containment”.

[1] Albuquerque, F. and Awadalla, D. (2020).  Roadside Fixed-Object Collisions, Barrier Performance, and Fatal Injuries in Single-Vehicle, Run-Off-Road Crashes. Safety 6(2), 27.