It will probably take at least several decades for completely self-driving vehicles to become commercially available, if they ever will. Yet, vehicles in which part of the driving task is automated, for example automated braking, accelerating and steering, are already available.

Traffic congestion occurs when traffic demand exceeds road capacity, or when an incident such as a traffic crash, a vehicle breakdown occurs or temporary roadworks take place, all of which temporarily reduce capacity and restrict traffic flow. Congestion crashes mainly occur at the tail end of a traffic jam. There, the speed of the traffic flow decreases sharply, which coincides with frequent and hard braking, and with a high risk of rear-end crashes.

If the average speed on a road increases, crash risk also increases, as does the risk of a serious outcome. This is true in general terms, but more so when motorised vehicles crash with unprotected road users, such as pedestrians, cyclists and (light) moped riders. Furthermore, speed differences between vehicles at any one time or place are related to a higher crash risk. Drivers that maintain a speed that is higher than the average speed on that road run a higher crash risk; drivers that maintain a speed that is lower than average do not.

In this factsheet wrong-way driving is defined as ‘a car driving in the wrong direction on a road with separated driving directions and consequently driving into oncoming traffic '. This relates mainly to motorways. Wrong-way driving crashes are rare. The outcome, however, is often severe. Most wrong-way driving crashes occur when a driver enters a motorway exit ramp or when a driver reverses direction on a motorway. Orientation problems (especially among the elderly) or recklessness (especially among young drivers) are the most common causes.

Visual information is of the utmost importance to road users. In darkness, both public lighting and vehicle lighting help road users take stock of the traffic situation and help them to be seen by others. Installing public lighting leads to a 50% reduction in the number of nighttime injury crashes. Disavantages of public lighting are, among other things, the risk of collisons with lamp posts, light pollution and the costs of material, maintenance and energy consumption. The road safety effects of a reduction in illuminance level on motorways vary according to the traffic situation.

Risky road user behaviour is behaviour that adversely affects road safety, such as driving under the influence of alcohol, drugs or medicines, speeding, inappropriate speed, distracted or fatigued driving, red light negation, and failure to use or misuse means of protection (motorcycle or moped helmet, seatbelt). Younger road users more often display risky behaviour than older road users, and men more often than women.

The mobile phone is symbolic of ‘distraction in traffic’. But apart from mobile phone calls, texting, or listening to music, many drivers, cyclists and pedestrians are occupied with all sorts of other activities that may distract them. Examples are: operating the navigation system, eating, drinking, talking to passengers or daydreaming.

Driving under the influence of drugs or impairing medicines reduces fitness to drive[i] and increases crash risk. Drugs have a numbing, stimulating or mind-altering effect on the brain, or a combination of these effects, which impair traffic task performance. For drug use in traffic, we (unfortunately) have to rely on research dating back to 2011.

The weather has an influence on road safety. Weather conditions partly determine the road conditions and the driver's behaviour. Most studies into the relation between weather and road safety are about the situation during rainfall. However, many other weather conditions are serious influences: fog, snow and black ice, low sun, hard wind, and high temperatures.

Driver fatigue is estimated to be a (contributing) factor in 15 to 20% of crashes, but estimates in individual studies vary widely. Drivers who are tired are less attentive and react less quickly and less adequately than drivers who are not tired. They also get irritated and frustrated more easily.