4/5 & 5/5 Sustainable Safety principle – Forgivingness and State Awareness

In June 2014 we adopted Sustainable Safety as our first policy. Here we will describe the five principles of Sustainable Safety. This article will talk about the last two principles and what they mean for cycling safety and road design.

We have previously discussed Functionality, Homogeneity and Predictability. We explained the need for clear classification of roads how the difference in speed and mass of vehicles creates a need for different types of cycle provision depending on the function of the road, and how consistent design used across an entire country makes the road conditions and peoples behaviour more predictable.

In Advancing Sustainable Safety by SWOV (http://www.swov.nl/rapport/DMDV/Advancing_Sustainable_Safety.pdf page 13) Forgivingness of the road environment and users is described as “injury limitation through a forgiving road environment and anticipation of road user behaviour” and State Awareness is described as “ability to assess one’s task capability to handle the driving task”.

That’s the theory. But what does this mean in practice?

Using the road system requires three different levels of task-based performance, skill-based, rule-based and knowledge-based. As road users are human, all three of these are prone to mistakes occurring, for a road network to be sustainably safe, it is important that the network is forgiving and reduces the possibility rule and knowledge-based mistakes. The most serious types of errors tend to occur around rule- and knowledge-based mistakes.

Skill-based actions tend to be routine actions that are carried out with little thought from the road user, examples of this are tasks like changing gears, accelerating, braking and steering. As these actions tend to be automatic, they do not offer the flexibility for the road user to be fully alert of what they are doing and to react consciously to what they are doing. It is even considered best that these acts are carried out at an automatic level leaving more mental ability of the road user to focus on dealing with the situations in front of them using rule- and knowledge-based performance.

Initially the act of learning is useful for a road user getting used to ‘handling’ the road so that the actions to control their vehicle become automatic. Additionally they should learn the rules that apply to them while on the road. In the UK for drivers we have the driving tests (theory and practical) to ensure that drivers have the minimum expected skills to carry out the task of driving on the road. However after learning there is very little enforcement to ensure that road users continue to drive with the skill, understanding of rules and knowledge to drive safely. There is, for example no period or age-dependent re-test.

Designing for State Awareness 

As it would be unsustainable and uneconomical to police every road user to ensure that they following the rules of the road, it is important that the road is designed in a way which makes it clear how the section should be used. Through the design ideas we have previously discussed, we have explained how roads should be defined by their function; and once its function is defined the road should be designed in a way that makes it obvious how it should be used, using features that are also consistent to provide better predictability.

An example of this from the Netherlands is on the slower roads brick surfacing is often used, the use of this surface makes it uncomfortable to drive fast, in additional to this narrow road widths make it feel more dangerous to drive quickly.

Amsterdam Slow Local Road

On higher speed roads, the use of wider lanes, smoother surfaces and junctions that sweep much wider allow faster speeds.

Additionally, the use of predictable patterns make it more obvious to them where to expect different types of behaviour and act as an aide to them remembering the rules of the road at these points. In the image below, the cycle path colour continues through the junction, both reminding drivers to expect cycles (using the colour red) and the continuous use of red, that shows it is the bike that has priority. In addition to this the pedestrian crossing works in similar way.

Amsterdam Side Road Crossing

Forgivingness

It is largely through the design towards homogeneous mass, speed and direction of traffic that the roads become forgiving to mistakes. Where speeds or mass of traffic is high enough to cause significant injury to less protected road users (like pedestrians and cyclists), the road should be designed to completely separate these users so that the conflict cannot occur, whereas vehicles of similar mass, speed and protection are generally much safer should a mistake occur.

At the point where motor vehicles do have to mix with cyclists and pedestrians, the road speeds are kept low through the design and layout used. Drivers are made to feel like they should be used at low speed (as discussed above), so that if there is a lapse in concentration, there should be time to recover from the mistake. This added time lowers the possibility of a collision occurring and the energy transfer in the collision should be low enough that any injuries sustained are not serious or fatal.

Here is another example. Angled kerbs can be used on cycleways to create forgiving environments. On an angled or chamfered kerb your cycle would run up the slope and you would come to a stop, rather than running into the vertical kerb with a likely consequence of you coming off your cycle.

Investigating Incidents

When collisions occur, it is important that the incident is investigated. This should not be done to identify who is at fault (this would be a separate investigation) but to identify what went wrong including any issues with the road design. This investigation allows the guidelines for road design to be scrutinised and changes made where issues are found. Having this allows the guidelines to develop and improve over time so that roads can be designed to be safer than they have been before. Ideally this would also extend to reported light collisions and ‘near misses’, as each event is a warning and an indication that something has gone wrong.

Conclusion

Through the application of the Sustainable Safety principles, we would quickly develop a road system that is safe for all road users. This means providing a network with roads designed for functionality, traffic movement designed around homogeneity of mass and speed, and using consistent designs to make the roads more predictable. As a result, road users would find an environment that is forgiving towards their mistakes and that makes it easy for them to be aware of their own actions and reactions.