Head Office SWEDEN www.vv.se Textphone: +46 243-750 90 Roger Johansson International Secretariat roger.johansson@vv.se Direct: +46 243 75880 Mobile: +46 70 6327373 Date: 2006-08-17 Reference: Road design and Safety philosophy, 1 st Draft The scope of this short paper is to outline, in a general way, the safety philosophy inherent in present road design, trace the origin of this philosophy, and to show the consequences on the global road safety crisis. It will be argued that deficiencies in the present road design philosophy are the main cause of the global road safety crisis, clearly indicating its man-made nature. Following an analysis of the problem suggestions are made for finding a solution. The solution is based on some of the principles in Vision zero, the Swedish road safety strategy. It includes a new basic mechanism for creating error-tolerance in the road system, and new design principles for road design. Traditional safety philosophy The traditional road-oriented safety philosophy has as its starting point the accident. Accident statistics are normally based on police reports made up on traffic accidents known by the police. This statistics have been used by road authorities world-wide for describing and analysing the road safety problem associated with roads and road design. It is important to notice that the concept of traffic accident and (bad) road safety is not synonymous. Many accidents could be an indicator of (bad) safety, but if the accidents do not lead to personal injuries they are not. Road safety is a health problem due to loss of full health (ref). A crash or accident without loss of health is no safety problem, only a cost. Sometimes this cost is the price we pay for safety like when we buy a safe care that protect us in a car crash. 1(7)
Accident statistics are never complete. That is, out of all accidents that happens on a road network, only a proportion are known by the police and reported in the statistics. If these omissions were random they could be ignored but they are not. They are for instance related to the kinetic energy in a crash. The higher the kinetic energy in a crash the more likely it is to be included in the accident statistics. A traffic accident as data source is also the starting point for the most widespread statistical fallacy in road administrations, namely the black-spot treatment. By focussing your safety actions on spots where most accidents occurred last year (or any other time period) you will always be successful. Next year accidents will be lower on those spots. But not as a result of your actions it is due to a phenomenon called regression towards the mean. Thus, the result of black-spot treatment is an illusion. A good source is...(ref) But the main thesis put forward in this paper is another, namely that by choosing the accident perspective, you get a safety philosophy that at its best reduces accidents, not necessarily personal injuries. And, as all modern definitions of the road safety problem define it as a health problem (health loss) the accident perspective misses the target. Accident analysis shows typically that 90-95% of all accidents are caused by road users. Society s most fundamental response to accident prevention has been rules and regulations for road user behaviour. The purpose of traffic legislation is mainly to simplify the tasks for road users making the risk of accident lower. In many cases this works as intended. But if the focus is shifted to the effect of the traffic regulation on health loss the pattern is less clear. (Examples are, for instance, traffic lights and pedestrian crossings ) When it comes to road design the totally dominant accident reducing strategy has been to increase space for drivers and vehicles. That is, wider lanes, wider roads, straighter roads, larger crossings etc. The reasoning behind this is straightforward and logical; if drivers run off the road lets make the road a little bit wider so there is room for manoeuvring the vehicle back into the lane and keeping the vehicle on the road; if drivers run off the road in bends, try making the road a little bit straighter thereby avoiding accidents in bends. This strategy has had some success in reducing the number of accidents. But even the effect on accidents and accident risks have been questioned (Ezra Hauer, 1999). But 2(7)
the strategy to create space for evasive action has not been successful in reducing fatalities and other severe injuries. In fact, everything else considered this strategy increases fatalities and other health losses. A wide, strait road has more fatalities than a narrow road with many curves if everything else is the same. The reason is simple: the most predominant effect of creating more space is an increase in driving speed, which means higher levels of kinetic energy in crashes. Higher energy levels, off course, lead to more severe health losses all other equal. This increase in speed has two reasons; first road administrations normally set a higher speed limit on a road that is wide and straight because they are said to have a higher safety standard, and drivers tend to drive faster anyway on these roads. This safety philosophy to build wide, straight roads (and streets for that matter) is the main contribution to the present global road safety crisis. The result is increase by one or two factors of 10 of the risks of severe personal injury of fatality, compared to the Vision zero design philosophy described later in this paper. No other design parameter has an impact of this magnitude. As an example Swedish 2-lane highways with a speed limit of 110 km/h had one of the most severe injury pattern recorded ever; out of three persons injured on these roads one was killed, resulting in 0,5-0,7 killed/10 km/year (in the 1990ies). Relatively new Chinese highways produce up to 20-25 killed/10 km/year. The main difference between the Swedish rural roads and the Chinese highways is that the latter have a large quantity of unprotected road users which are separated from motorized vehicles only by the wideness of the roads and traffic regulations e.g. pedestrian crossings. It has been shown on these Swedish roads mentioned in the example that the fatalities can be reduced by 85-90% by applying mid- and side barriers. The Chinese highways mentioned above could, at least in principle, be rebuilt reducing fatalities with up to 99%. A note must be made on motorisation and its effect on overall safety in a country. Sweden has approximately 0, 5 cars/inhabitant whereas China is only in its beginning as a motorised country with 30 million vehicles and a population of 1300 million inhabitants. WHO (Jonathon Passmore, 2006) has noted that the number of persons killed in a country turns from an increasing trend to a decreasing trend when the GNP/capita reaches approximately 8000 US$. A hypothesis based on this data could be that the change in composition of traffic, that is the mixture of protected/unprotected road users reaches a critical limit at that stage of economic development (8000 US$). That is, the separation between vehicles and unprotected road users reaches a certain level which has an overall good effect on road safety. It should also be noted that this separation in (most) societies is spontaneous and not 3(7)
engineered. It is a function of more and more people become motorised (car or bus) and the number of unprotected road users decrease, especially on rural roads. The challenge in a developing country is of course to engineer this separation in an early stage of motorisation. Vision zero philosophy Vision zero is a safety strategy that focuses on health. Health, in this context, can be defined as a state where crashes or collisions do not lead to health loss. If a car hits a crash barrier with damage to the car and the barrier but with no personal injuries, it is not a safety issue only a cost. If an injury is minor e.g. a bruise it can be accepted. Some injuries are thus too trivial to be considered health losses. The human tolerance for biomechanical forces is in this perspective the starting point for the design of a safe traffic system. This tolerance is a given factor it cannot be affected to any significant extent. For instance if cars hits pedestrians in 25-30 km/h most of them survives. However, if the cars instead do 50 km/h, most pedestrians will die. The trick from an engineering point of view is to design and construct a traffic system where this human tolerance isn t exceeded. Whereas the general strategy for safe road design from the accident perspective was to increase space for drivers and vehicles, the corresponding strategy from a Vision zero perspective is to manage kinetic energy in crashes and collisions. It is kinetic energy that kills and injures the road user not the accident. By managing the crash in terms of the energy that is transferred to the human body, an error tolerance can be built into the traffic system. In fact, an error tolerance was also the intention behind the idea to give drivers space in the traditional safety paradigm. Space would give room for evasive manoeuvres thus avoiding the accident; the problem was that it never worked the way it was intended. The management of kinetic energy in crashes and collisions can be broken down to the following principle for road and street design; Integration and Separation. You manage kinetic energy by integrating compatible traffic elements and by separating incompatible ones. Here are some boundary values: 1. Unprotected road users should not be exposed to motorised vehicles at speeds exceeding 30 km/h 2. If 1. cannot be satisfied then separate or reduce vehicle speed to 30 km/h 4(7)
3. Car passengers should not be exposed to other motorised vehicles at speeds exceeding 50 km/h in 90 degree crossings 4. If 3. cannot be satisfied then separate or reduce angel or reduce speed to 50 km/h 5. Car passengers should not be exposed to oncoming traffic (other vehicles of approximately same weight) at speeds exceeding 70 km/h or 50 km/h (if oncoming vehicles are of considerably different weight) 6. If 5. cannot be satisfied then separate, homogenize weights or reduce speeds to 70(50) km/h 7. Car passengers should not be exposed to the road side in speeds exceeding 70 km/h or 50 km/h (if road side contains trees or other narrow objects) 8. If 7. cannot be satisfied separate or reduce speed to 70(50) km/h It should be noted that a separation is always a physical separation and never a temporal (traffic lights). Spatial separations could be tunnels, bridges or other crossings in different levels, crash barriers or barriers for pedestrians or different roads for different traffic elements (e.g. bicycle roads). A wide space is not to be considered as a separation. The result of an application of these principles to the design of roads and streets can be described in many ways. One is to look upon the road and street environment from the perspective of the road user. From the perspective of the driver the following can be observed: In areas with many unprotected road users maximum speed is 30 km/h. Expect narrow lanes, bumps and unprotected road users passing the streets even in-between crossings. Where driving speeds are 50 km/h lanes are still narrow, pedestrians and bicyclists do not cross in-between crossings due to mid-street pedestrian fences and 30 km/h where unprotected road users cross. For all roads and streets with speeds higher than 50 km/h drivers should expect barriers both to the right and to the left of their car. In +50 km/h environment unprotected road users are never mixed with cars. 5(7)
The general solutions for crossings are roundabouts. If capacity is a problem, add traffic lights. If unprotected road users are present, canalize and lower car speed to 30 km/h in crossings. Pedestrians and bicyclists generally have their own roads. Cars are separated from this network by their crash barriers in +50 km/h environments. In 30-50 km/h environments pedestrians are if necessary hindered to pass streets by use of pedestrian fence in mid-street. Always when pedestrians and bicyclists share space with cars, car speed is maximum 30 km/h. Discussion It is a common opinion among road administrations that crash barriers can be dangerous. This is not correct. The danger comes from barrier ends. The wide spread application of crash barriers in most countries is to put up relatively short crash barriers where there is a height difference between the road and the side of the road or where there is water by the side of the road. The safety effect of this could be positive (if the barrier is long enough), neutral (if the benefit of the barriers length is balanced by the hazard of the barrier ends) or negative (if the barrier is to short). How long a barrier must be in order to counteract the negative effect of its ends is not known, but a fair guess would be at least more than 100 meter. The solution to the problem is, of course, to take away the bar ends. That is, continuous barriers. A crash with a modern vehicle into a modern barrier designed according to European standards is a crash without severe personal injuries. There is one type of road that do not follow the traditional pattern, and that is motorways (expressways) with continuous crash barriers on both the median and right side of the road found in many parts of the world. If the traditional strategy would have been applied you should have expected a wide median without barrier and a side area without barrier. These motorways with continuous barriers are, of course, very safe. A hypothesis on how this has happened is as follows: these motorways were initially built without barriers as tradition and manuals say. Then traffic increased and additional lanes were built. When the new lanes were added the midsection became very narrow with risks for head-on collision. Or the side area became to narrow with risk of crashing into fix objects by the side of the road. 6(7)
Therefore mid-barriers or side-barriers were added. This procedure (by accident) turned out to create very safe motorway and is now standard procedure in many countries. There are some applications of this road design strategy to manage kinetic energy by applying the principles of Integration and Separation. The safety principles inherent in Lugna gatan is very spot on and a recent extension of the Sunflower project shows very clearly that unprotected road users have a substantial lower fatality risk/personkm compared to the Dutch and British. The Swedish 2+1 roads with mid barrier and alternating two or one lane(s) are also very near these principles. Results show at present a reduction of fatalities by 85-90% a figure which at least in theory should be possible to get to 90-95%. But Swedish rural roads are easy because there is so few pedestrians and bicyclist. In many highly populated developing countries pedestrians and bicyclists are almost as numerous on rural roads as in villages or towns. The need for special roads for these road users is therefore large. The costs for these roads are, however, not high in comparison. 7(7)