Sustainable Safety

Sustainable Safety (“Duurzaam veilig” in Dutch) is the name of the Dutch approach to achieve a better road safety. This policy is lesser known than ‘strict liability‘ and underestimated. Where strict liability is a cure after something went wrong, sustainable safety does much more and at a different time. The main objectives of this vision are preventing severe crashes and (almost) eliminating severe injuries when crashes do occur. It was introduced and quickly adopted by all road managers in 1992 and has since been very successful. In 2005 it was revised and extended. The approach began with establishing that the road system was inherently unsafe. The goal was to fundamentally change the system by taking a person as a yardstick. The guidelines for design were to be the physical vulnerability of a person, but also what a person can and wants to do (humans make mistakes and don’t always follow rules). There is now an integral approach to the road system which refers to ‘human’ (behavior), ‘vehicle’ (including bicycles!) and ‘road’ (design). Roads and vehicles must be adapted to the human capabilities and the human has to be educated enough to be able to operate a vehicle on a road in a safe manner. The approach is pro-active, it wants to remedy gaps and mistakes in the traffic system before crashes occur. So Sustainable Safety is about a lot more than just infrastructure.

Sustainable Safety is based on five principles: 

  1. Functionality (of roads)
  2. Homogeneity (of mass, speed and direction of road users)
  3. Predictability (of road course and road user behavior by a recognizable road design)
  4. Forgivingness (of both the road/street environment and the road users)
  5. State awareness (by the road user)

The principles are based on scientific research and theories from traffic engineering, biomechanics, and psychology. Since the 2005 revision the principles are also based on infrastructure, vehicles, intelligent transport systems, education and enforcement of laws and regulations.

1. Functionality of roads

To the Dutch the most ideal situation is when roads and streets have only one single purpose. To achieve this mono-functionality a hierarchy of roads was introduced.

  1. Through Roads for high volumes of fast traffic on longer distances.
  2. Local Access Roads from which end destinations can be reached.
  3. Distributer Roads which connect through roads and local access roads.

All Dutch streets and roads have been classified (under a legal obligation) and are or will be re-designed to the Sustainable Safety principles by the road managers. This led to areas where people stay (residential areas and areas for shopping/sporting/theatre etc.) and designated space used for the flow of traffic in order to transport people from A to B. Under the Dutch vision these functions cannot be mixed.

2. Homogeneity of mass, speed and direction of road users

Large differences in speed and mass of different road users in the same space must be eliminated as much as possible. Road users can best be forced to travel at lower speeds by road design. This works better than with signs. If crashes occur at lower speed differences they cause a lot less damage to the most vulnerable road user. Where speed differences cannot be eliminated types of traffic must be separated. On roads with higher speeds road users travelling in opposite directions should be separated by a division as well, to further eliminate conflicts. Cycle paths and pedestrians are always separated from these through roads, following the principle of homogeneity of mass as well as speed. Because of this principle the Dutch will never implement a combined bus/cycle lane as is common in some other countries. Instead there sometimes even are bus lanes separated from other motorized traffic because the mass of cars and buses do not match either. Eliminating crossing movements is possible with roundabouts because on roundabouts traffic flows in less conflicting directions than on an ordinary traffic junction.

3. Predictability of road course/road user behavior by recognizable road design

Road design should be so consistent that road users instantly understand what they can expect and what is expected of them on a certain type of street or road. The road design itself gives information about the type of road/street. If the street is paved with bricks, there are parked cars and the street is shared with cyclists and gives access to homes, the road user will instantly know and feel this is a 30km/h (19mph) local access street. However, if the road has two carriageways separated by a median, there is no parking and cyclists have their own cycle paths, it is clear to the road user that this is a through road.

4. Forgivingness of both the road/street environment and the road users

Humans make errors and willingly or unwillingly break rules. This is a given that cannot be changed. So roads and streets should be designed in such a way that this natural human behavior does not lead to crashes and injuries. An example is a shoulder with a semi-hard pavement. A road user coming off the main road will not crash immediately; the semi-hard shoulder will give this road user the ability to get back to the main carriageway. The equivalent for cyclists is a curb with a different angle; 45 degrees in stead of 90 degrees. Hitting this curb with your front wheel will not immediately result in a fall. Forgivingness towards other road users is enhanced when road design leads to a predictable behavior of road users. A result of this principle is that motorized traffic sometimes gives priority to cyclists even if they don’t have it. Because it is so clear where the cyclists want or need to go the motorist anticipates their behavior and gives the cyclist more room than he or she is legally obliged to, often to the surprise of especially foreign cyclists.

Closer look to a 'forgiving curb'. It has a 45 degree angle. Less dangerous than the older curbs with a more common 90 degree angle. A cyclist accidently hitting this new type of curb is less likely to fall.
Closer look to a ‘forgiving curb’. It has a 45 degree angle. Less dangerous than the older curbs with a more common 90 degree angle. A cyclist accidently hitting this new type of curb is less likely to fall.The picture also shows the separation of traffic with a different mass and speed, from left to right: pedestrians on the sidewalk, the red cycle track and in the center of the road motorized traffic. On the other side of the road there is a again a cycle track and a sidewalk.
5. State awareness by the road user

This principle is about the ability of road users to assess their own capabilities to perform tasks in traffic. This has to do with understanding vehicle operation and knowing how speed changes the behavior of the vehicle to understand what speed is safe in a certain situation. But it also has to do with the assessment of speeds of other traffic users to estimate crossing times for instance. These abilities can be improved by education but there are limits, for instance when road users are children or elderly.

Effects of Sustainable Safety

Many countries have seen a considerable drop in traffic injuries and deaths since roughly the 1970s. Reasons were the introduction of seatbelts, drunk-driving laws, helmet laws for motorcyclists and mopeds, car cages and airbags. But in the Netherlands there also was a dramatic drop in injuries and deaths of the most vulnerable road users: cyclists and pedestrians. Traffic researches attribute this difference to the introduction of Sustainable Safety.

Ten years after the introduction researches found a traffic death and injury reduction of on average 6% per year. And that wasn’t the only positive outcome. When the costs of the measures that had to be taken were compared with the benefits of the reduced traffic injuries and deaths it was found that the benefits outweighed the costs by a factor of four.

Students of the Northeastern University in Boston compared the Netherlands with the US. After analyzing all they had learned on their study tour in the Netherlands in 2010 they found the following: “In the 1970’s, the Netherlands and the US had the same traffic fatality rate (fatalities per person). Both countries have seen dramatic decreases in traffic fatality rates over the past forty years […]. However, the Netherlands has put much more emphasis than the US on making their roads inherently safer. The result: the Netherlands has reduced its traffic fatality rate to less than half of the US traffic fatality rate; the Netherlands now has a traffic fatality rate that’s only 23% of its 1970 rate, compared to the US whose traffic fatality rate is 54% of its 1970 rate.”

So the system of Sustainable Safety is undisputedly successful, it is worth to be studied.

SWOV Factsheets (English, PDF): sustainable safety principles / sustainable safety background
SWOV Factsheets (Dutch, PDF): duurzaam veilig principes / duurzaam veilig functionaliteit en homogeniteit
Sustainable Safety Wiki (English) by students of the Northeastern University of Boston

This post, written by me, was originally published on a different platform.

66 thoughts on “Sustainable Safety

  1. Reblogged this on 0 to 100 and commented:
    I have never reblogged a post before, so I am curious what happens. Since most people I talk with in the US have only heard of Vision Zero and have never heard of Sustainable Safety, have you heard of Sustainable Safety? How do you think Sustainable Safety compares with Vision Zero?

    1. Hello Ray,

      FWIW This particular blogpost is my go-to must-read primer for understanding and explaining Dutch Sustainable Safety. I’m always returning to it.

      In my opinion the NL’s Sustainable Safety is much better than V0 as it holistically encompasses urban planning; in fact the aims of good urban planning (that now seem to be almost universal in developed countries) are what drive SS.

      SS dictates to traffic engineers what is required of them, and why, and crucially doesn’t leave it to the autosupremacist traffic engineering “profession” to do what they’ve been doing for the last 60+ years.

      Below is an article by SWOV comparing the two methods, with links to another discussion about the two (that I’ve not yet read).

        1. I am in Australia, where both V0 and SS were adapted into its “Safe Systems Approach” in around 2005. The latter was done in name only, obviously, hence why 15 years later we don’t have ubiquitous nice quiet residential streets to live in like the NL does, and our national cycling mode share is a pathetic 1% and falling.

          Just one example of how inanely, stupidly autosupremacist our “road safety” people are here, the university “expert” given the responsibility for rolling out Australia’s “Safe Systems Approach” (since dropped as a policy) to the Australasian traffic engineering “profession”, couldn’t grasp – in a workshop full of traffic engineers – that the NL’s SS core tenet of road *mono-functionality* was by definition totally incompatible with the Sirensong/snake oil concept that is the UK’s “Link and Place”, which Australia has also adopted without credible evidence.

          For me it was like being in The Simpsons “monorail” episode, except the whole room was even dumber than Homer was, with “Mono meaning one, and functionality meaning functionality” well beyond their brain capacities.

          1. I like Sustainable Safety but not Vision Zero. I appreciate a pro-active approach but without the use of zero.

  2. The extensive use of dedicated bus lanes raises the question of why don’t they use light rail rather than buses.

  3. Reblogged this on CycleBath and commented:
    I think the critical bit that UK Highways needs to listen to is: “Many countries have seen a considerable drop in traffic injuries and deaths since roughly the 1970s. Reasons were the introduction of seatbelts, drunk-driving laws, helmet laws for motorcyclists and mopeds, car cages and airbags. But in the Netherlands there also was a dramatic drop in injuries and deaths of the most vulnerable road users: cyclists and pedestrians. Traffic researches attribute this difference to the introduction of Sustainable Safety.”

    1. Then how about us building the bicycle paths? About 10.000 times as effective as laws

  4. The functionality problem with roads in North America (and you too Australia, NZ and UK) is so bad that someone even came up with a word to describe them: stroads. A combination of the word road and street. Roads are for 100-130 km/h traffic at high speed on motorways or autowegen or 70 km/h distributors in the urban area with no local access and partial control of access. 50 km/h distributors in the Netherlands have as few stops as possible and if possible, have no local access. Every junction is a roundabout if possible, and speeds are kept to 50 km/h, 30 km/h if they cross the path of a cycleway or footway when possible. In North America, we combine 4-6 lane roads with 12′ (I prefer 3.7 metre) lanes and often parking, wide corner radii and between 50 and 60 km/h speed limits. Just fast enough to be dangerous but too slow to be efficient for going anywhere in a hurry. This is why service roads and downgrades to smaller distributors, ideally a single lane in each direction, is important, especially in the urban area.

  5. I suggest that you use the fact that cyclists are usually protected with a verge on distributor and through roads as an example of forgiveness. If a car has a very hard time getting onto the cycle path, it will happen less by accident.

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