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The impact of speed on accidents and injuries

31 August 2022
Article by Francisco Castro, researcher in accident dynamics at INEGI.

Speed ​​is one of the main risk factors in road accidents, being directly related to the occurrence of the accident and consequently to the severity of the injuries that may result. The accident rate in Portugal continues to be one of the highest in Europe and according to data from the National Road Safety Authority, speeding is the most common offense committed by the Portuguese1, being the leading cause of death in young people worldwide.

Determining the speeds and avoidance maneuvers associated with the accident are key factors to determine, as is the probability and degree of injury generally associated with that speed. INEGI's Accident Investigation Center (CENPERCA) therefore carries out studies and scientific reconstructions of road accidents, at the request of entities such as Courts (Civil, Criminal and Public Prosecutor), forces of authority, or private entities.

Excessive speed is present in 90% of accidents with fatalities that arrive at CENPERCA. Although not the only factor, it is without a doubt the factor with the greatest impact, as can be seen in the following examples of accidents analyzed by CENPERCA. The increase in impact velocity increases the risk of serious injury and the associated risk of fatality.

Collisions with people

In the case of being run over at 30 km/h, 95% of people survive, however they can suffer minor to severe injuries. The situation worsens when the speed approaches or exceeds 50 km/ h, where the pedestrian has a high probability of serious injuries and a probability of about 10% that they could lead to death. From 50 km/h onwards, the probability of death increases exponentially with speed.

Considering two of the examples that the Accident Investigation Center analyzed, one being a collision with a fatal victim, and a second being a collision resulting in serious injuries, it appears that speed once again had an impact on the final outcome of each accident. In the first accident, the vehicle was traveling at approximately 66 km/h at the time of being run over, causing the death of the pedestrian, while in the second accident, the vehicle was traveling at approximately 31 km/h and the pedestrian was seriously injured - However, it is important to note that Injury intensity depends on several factors such as age, sex, weight, height, impact position, height of the vehicle's center of gravity and pedestrian behavior moments before being run over (defense reactions).

Vehicle collisions

A collision between two vehicles can trigger several injuries. An example of a side impact between two vehicles with a collision speed of approximately 80 km/h was enough for one of the occupants who suffered the side impact to sustain several serious injuries – probability of serious injury of 95%. If the speed were below the speed limit of the road - 50 km/h - the maximum probability of injury would be only 50 %. For a collision speed of 30 km/h in a side impact, the probability of serious injury is already reduced to 10 %.

Speeding is also directly related to the significant increase in stopping distances. A vehicle (on dry ground) traveling at approximately 50 km/h needs about 12.3 meters to stop, while a vehicle traveling at 30 km/h needs 4.4 meters to stop.

It is possible to conclude that speed is a major factor in the occurrence of road accidents. Speed ​​may determine whether a driver has the space and time to stop in time and, if not, how fast they will crash and what the consequences are, as well as how likely the level of injury associated with that speed is.

The investigation of accidents, through its scientific reconstitution using computer simulations and analysis of multibody dynamics, is important in order to determine the respective causes, as well as in the creation of awareness plans for the general population.



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