Speed, by definition, directly affects road transport. It defines the mobility rates and options of persons and goods travelling from one location to another (Aarts, L., & Van Schagen, I., 2006). In today’s modern life, citizens demand a high degree of mobility and the possibility to travel fast by air, rail or road has become an integral component of our societies. However, driving speeds also have a direct impact on the risk of the driver and all road users, and it directly influences their involvement in potentially fatal or severe crashes as well as on noise and pollutant emissions (Elvik R., 2013).[/caption]
Speed has been found to be a major contributory factor in around 10 to 15% of total crashes and in around 30% of fatal crashes (European Road Safety Observatory, 2021). Not only does speeding make a crash more likely to happen, it also increases the likelihood of severe injuries or death from a crash (European Commission, 2019). Both excessive speed (driving above the speed limit) and inappropriate speed (driving too fast for the conditions, but within the limits) are important crash causation factors (NRSO, 2019).
In addition, speed has a uniformly negative effect on the environment overall. The level of exhaust emissions, fuel consumption and noise increase with speed (NRSO, 2019). Speed effects the quality of life of urban residents, especially the safe mobility of vulnerable road users (NRSO, 2019).
Although it is perceived as reducing travel time, in reality, little time is saved by speeding. For example, if a driver travels at 65 km/h instead of 60 km/h, the saved time is a maximum of 46 seconds over a 10-kilometre distance. However, the risk of being involved in a crash with casualties is double (Transport Roads & Traffic Authority, 2011).
One may wonder how is it possible speed still being as important for road safety as it was in the past, since the new vehicle safety systems should have made speed a less crucial road safety factor. Modern cars are better equipped both to avoid crashes and make them less serious (by protecting occupants better) that cars were 15-20 years ago. On the other hand, their speed performance has increased. (Elvik, 2019).
Before cars had, for example, electronic stability control and emergency brake assistance, they may have been unable to avoid a crash both at 55 and 50 km/h, meaning that this difference in speed would not necessarily be associated with a difference in the number of crashes. However, with these systems, a driver might just be able to make a rapid evasive manoeuvre and/or brake hard enough to avoid the crash or reduce its severity at 50 km/h but not at 55 km/h (Elvik, 2019).
Even exceeding the speed limit by a small margin can have a considerable impact. As an example, a driver noticing a pedestrian crossing the road can be considered. If the car is travelling at 50 km/h and the driver brakes when the pedestrian is 29 meters away, there will be enough space in which to stop without hitting the pedestrian. If the vehicle speed is increased by just 10 km/h, the situation changes dramatically. At 60 km/h, with the pedestrian 29 meters away and the driver braking at the same time, the car will be travelling at 44 km/h when it hits the pedestrian (Transport Roads & Traffic Authority, 2011).
When speed increases, the risk of a crash and of its severity increases as well (International Traffic Safety, 2018). The severity of a crash follows from the laws of physics. The increase in crash risk is usually attributed by the fact that when speed increases, the time to react to changes in the environment is shorter and manoeuvrability of a speeding car is smaller.
The relationship between speed and crash risk is a power function (Elvik, 2009): With increasing speed, the crash risk increases more as the absolute speed is higher. Indeed, 1 km/h increase in speed equals to 3% increase in crashes (European Road Safety Observatory, 2021). In fact, The European Transport Research Council (ETSC) estimates that reducing the average speed by 1 km/h on all roads across the EU would save over 2000 lives per year (European Road Safety Observatory, 2021).
The relationship between speed and changes in road safety is indeed causal. This is based on the following arguments:
1. There is a strong statistical relationship between speed and road crashes. It is difficult to think of any other risk factor that has a more powerful impact on crashes or injuries than speed. A 5% increase in average speed leads to approximately a 10% increase in all injury crashes and a 20% increase in fatal crashes (OECD/ECMT, 2006).
2. The statistical relationship between speed and road crashes is very consistent. When speed is reduced, the number of crashes or injured road users also decreases in 95% of the cases. When speed goes up, the number of crashes or injured road users goes up in 71% of the cases (Elvik, 2004). While it may to some extent be possible to offset the impacts of higher speed by introducing other road safety measures, a reduction in speed will almost always improve road safety.
3. The relationship between speed and road safety appears to hold universally and is not influenced by, for example, the country in which it has been evaluated, when it was evaluated or the type of traffic environment in which it was evaluated.
Furthermore, the effect on crashes of a given relative change in speed is largest when initial speed is highest (Elvik, 2013). It can be estimated that a 10% reduction in the mean speed of traffic will result in a 37.8% reduction of the number of fatalities (Elvik, 2004). The analyses suggest a 49.8% reduction in fatal crashes and a 28.9% reduction in injury crashes when reducing the initial speed by 10 km/h (Aigner-Breuss, 2017).
According to the NHTSA’s report 29% of fatal crashes, 13% of injury crashes and 10% of property-damage-only crashes in 2020 were speeding-related (NHTSA, 2022). Excessive speed is a major problem in all motorised countries. An estimate for Norway shows that if all drivers were driving below speed limits, the number of fatalities would be reduced by about 20% (Elvik, 2009).
In conclusion, speeding – which encompassed excessive speed or inappropriate speed is dangerous. As well as being a causation factor in around one third of fatal crashes, speed is an aggravating factor in the severity of all crashes (ECMT, 2006). That is why co-ordinated actions should be taken by the responsible authorities to bring about an immediate and durable response to the problem of speeding.
- Aarts, L., & Van Schagen, I. (2006). Driving speed and the risk of road crashes: A review.
- Aigner-Breuss, E. B. (2017). Speed of Traffic. European Road Safety Decision Support System, H2020 project SafetyCube.
- Elvik, R., Christensen, P., & Amundsen, A. (2004). Speed and Road Accidents: An Evaluation of the Power Model. Oslo: Institute of Transport Economics (TOI).
- Elvik, R. (2013). A Re-Parameterisation of the Power Model of the Relationship between the Speed of Traffic and the Number of Crashes and Crash Victims, p.854-860.
- Elvik, R., Vadeby, A., Hels, T., & Van Schagen, I. (2019). Updated estimates of the relationship between speed and road safety at the aggregate and individual levels. Accident Analysis & Prevention, 123, 114-122.
- Elvik, R. H. (2009). Handbook of road safety measures. United Kingdom: Emerald Group Publishing limited. European Road Safety Observatory. (2007). Speeding. erso.eu.
- International Transport Forum (2006). Speed Management Report , 2006, p.14. OECD Publishing.
- International Traffic Safety (2018). Speed and Crash Risk. OECD/ITF.
- Lu, Q. L., Qurashi, M., & Antoniou, C. (2023). Simulation-based policy analysis: The case of urban speed limits.
- National Highway Traffic Safety Administration - NHTSA (2022). Traffic Safety Facts, Speeding. U.S Department of Transportation.
NTUA Road Safety Observatory - NRSO (2023). Speeding Kills. Retrieved from https://www.nrso.ntua.gr/speeding-kills/. Accessed on 31/05/2019.
- Transport Roads & Traffic Authority (2011). Why is speeding a problem? NSW Centre for Road Safety.