The five Sustainable Safety principles
Sustainable Safety now has five main principles:
- Functionality of roads,
- Homogeneity of mass, speed, and direction,
- Recognizability of the road design and predictability of the road course and road user behaviour,
- Forgivingness of the environment (physical) and between road users (social),
- State awareness by the road user.
The last two principles have been added to the Sustainable Safety vision in the 2005 update.
These five principles are based on scientific theories from road engineering, biomechanics, and psychology. They are explained in more detail in the book "Advancing Sustainable Safety" and have been detailed for the areas of: infrastructure, vehicles, intelligent transport systems, education, and regulations and enforcement. The principles have also been worked out for specific subjects and target groups: speeds, alcohol and drugs, the young, cyclists, pedestrians, motorized two-wheelers, and freight transport.
Functionality
A sustainably safe road network has a functional layout, based on three main road types. The two most 'extreme' types are, respectively, main roads, for traffic dispersion, and access roads, for access to the destination. The third type, the distributor roads, forms a link between the other two types, both literally and figuratively.
Homogeneity
Sustainable Safety aims at homogeneity in mass, speed, and direction. This means that vehicles with large differences in mass, speed, and direction must be physically separated from each other. For example, cars and vulnerable road users are incompatible, and so are lorries and other vehicles, or motor vehicles driving in opposite directions. Conflicts between these vehicle types will almost inevitably have a severe outcome. With separate infrastructures or dual carriageways this type of conflict can be prevented.
Where physical separation is not possible, for example at grade level junctions, the speed must be reduced. It should be sufficiently low that all possible conflicts will end safely, i.e. without any severe consequences. Measures that can be used here are lowering of the speed limit and speed reduction, for instance by constructing roundabouts or raised junctions and raised pedestrian crossings.
Recognizability
Road users should know which driving behaviour is expected of them and what they can expect from others. In a sustainably safe traffic system, road users should 'automatically' drive as is to be expected. Generally, people make fewer mistakes when engaging in automatic behaviour, than while driving using reasoned actions.
The desired driving behaviour can only be incited with a uniform road design which is well tuned to it. Drivers need to recognize the road type and automatically behave accordingly. This must be the case for the entire road network: not only the other road users' driving behaviour should be predictable, but the road course as well.
Forgivingness
Forgivingness in the physical sense means that the road design ensures that the outcome of any possible crashes is as favourable as possible. A vehicle that goes off the road should not hit any obstacles or fixed objects, because this can result in severe injury. The vehicle itself should offer protection to both its occupants and to the collision opponent.
Forgivingness in Sustainable Safety also has a social meaning. Through anticipatory behaviour, the more competent road users should provide more space for the less competent road users. This will prevent errors made by the latter group being 'punished' with a collision.
State awareness
State awareness refers to the road user's capacity, or the opportunity, to correctly judge his own fitness to drive. This means that he must know which skills he possesses and whether they are sufficient to drive safely. But road users should also be capable of knowing if they are, temporarily, unfit to drive due to alcohol, stress, or fatigue.