Vision Zero – Implementing a policy for traffic safety
The scope of this paper is to outline, in a general way, the safety philosophy inherent in present road- andstreet design, trace the origin of this philosophy, and to present the principles for a new design of streetsand roads. It will be argued that deficiencies in the present road design philosophy are the main cause ofthe global road safety crisis, clearly indicating its man-made nature. A brief description is made of thedecision process leading to the establishment of Vision Zero as Sweden’s Traffic Safety Policy in 1997.
Following an analysis of the problem, suggestions are made for finding solutions. The solutions arebased on some of the principles in Vision Zero. They include a new basic mechanism for creatingerror-tolerance in the road system, and new design principles for road- and street design.
The tradition of “blaming the victim” is hereby questioned and focus is put on the need for professionalsto act based on these new standards. During the last 10 years the fatalities in Sweden have droppedfrom approximately 550/year to 450/year. Roads redesigned with median barriers have an 80% reductionin fatalities. Streets with 30 km/h design speed show similar results. This indicates that measures derivedfrom Vision Zero strategy are effective but that large scale implementation has not yet been done.
1. The process
The Swedish Road Administration (SRA) had an overall responsibility for Road Traffic Safety in Sweden since 1993. This responsibility was further clarified by the Government in 1996. Sweden has very small Ministries (number of personnel). As a consequence Administrations like the SRA often have semi-political tasks like development of policies and targets. Decisions on policy, long term targets and overall budgets are made by the Government or the Parliament but development is made in the Administration.
Following the elections in the autumn 1994 Sweden got a new Minister for Transportation. The Minister declared that traffic safety would be one of her priorities. A dialog was started between the Minister’s Staff and the SRA on how the Minister could make traffic safety a prioritized subject.
In the spring of 1994 the SRA together with the major stakeholders for traffic safety had presented a short term program for action for the years of 1994–2000. It had the character of continuing earlier work but with more emphasis on cooperation between key actors and focus on results. Directly after this program was launched the SRA started to develop some basic ideas for a long term strategy for traffic safety. It had been recognised for some time that the contemporary traffic safety paradigm had some problems (Johansson, 1991). Part of this problem was a lack of expected benefits of many measures, something that was recognised by among others Gerald Wilde (best described in Wilde, 2001). A comprehensive overview can be found in OECD (1990).
The new safety paradigm, Vision Zero is built around the basic idea that even if not all crashes or collisions can be avoided, all severe injuries can, in principle, be avoided. The basic idea was to build a “safe system” where all predicted crashes and collisions had tolerable health losses. The Minister and her Staff recognised that it was possible to work with the ideas behind Vision Zero in a political setting and quickly adopted the basic ideas, developed a text (translated in Belin et al., 1997), and took it to the Parliament in 1997, where it was accepted by all political parties (Tingvall, 1998). Since then, the Parliament has repeated this decision on a number of occasions. The notion of “Vision Zero” has become synonymous with the concept of “high political ambitions” in a number of other areas as well. The Government in 2008 took a decision on a Vision Zero for suicide. Much of the political debate on Vision Zero between 1995 and the Parliament’s decision in 1997 was concentrated on the question”How many fatalities can we accept?” At this time Sweden had around 500 fatalities in road traffic per year. Comparisons where made with the safety level for other transport modes, (clearly a zero fatality goal), occupational safety (about 50 fatalities annually), electricity (about five fatalities annually). From this political analysis it was concluded that a zero fatality target was the only justifiable target for road traffic.
During the same time period SRA and its network concentrated work on developing strategies for radically lowering fatality risks in road traffic, typically aiming at reducing fatality risks with a factor 10. Examples follow later in this paper.
2. Vision Zero
In 1997 the Swedish Parliament passed a bill on Traffic Safetywhere it was stated that:
“Vision Zero means that eventually no one will be killed or seriouslyinjured within the road transport system.”
Vision Zero does not presume that all accidents that result inpersonal property damage or in less serious injuries must be eliminated. These occurrences are not considered to be an essential elementin the road traffic safety problem even if they can entail largecosts for the State, county councils, municipalities and individuals. Rather, focus shall be placed on those incidents that lead to a personbeing killed or seriously injured. Vision Zero also proposes anethical approach to the health problems associated with roadtraffic:
“It can never be ethically acceptable that people are killed orseriously injured when moving within the road transport system.”
Vision Zero is said to be a long-term goal for the design andfunctioning of the road transport system. What is important is torealise that the Vision Zero approach will alter the aim of the workon road traffic safety; i.e., from attempting to reduce the number ofaccidents to the formulation of an explicit goal: to eliminate the riskof chronic health impairment caused by a traffic accident. This newapproach will also alter the question from “what can we do?” to “what must we do?”
Vision Zero presumes a new division of responsibility for roadtraffic safety within the road transport system. The responsibilityfor road traffic safety should be introduced along the followinglines.
1. The designers of the system are always ultimately responsiblefor the design, operations and use of the road transport systemand are thereby responsible for the level of safety within theentire system.
2. Road users are responsible for following the rules for using theroad transport system set by the system designers.
3. If road users fail to obey these rules due to a lack of knowledge, acceptance or ability, or if injuries do occur, the system designersare required to take the necessary further steps to counteractpeople being killed and seriously injured.
Taking the Vision Zero approach means that paying attention tohuman life and health is an absolute requirement in the design andfunctioning of the road transport system. This implies that roadtraffic safety issues, in similarity to environmental issues, mustbe clearly integrated in all the processes that affect road trafficsafety in the road transport system and be based on the following:
“The level of violence that the human body can tolerate withoutbeing killed or seriously injured shall be the basic parameter in thedesign of the road transport system.”
It is upon this principle that the future society with safe roadtraffic can develop: through designing and constructing roads, vehicles and transport services so that the level of violence thatcan be tolerated by the human being is not exceeded; and throughthe effective contribution of different support systems such asrules and regulations, education, information, surveillance, rescueservices, care and rehabilitation. With this as the basis, there willbe a positive demand for new and effective solutions that can contributeto a road transport system where human needs, prerequisitesand demands are in focus.
“It is true, that 95% of all crashes or collisions depend on humanerror, but according to Vision Zero philosophy, 95% of the solutionsare in changing roads, streets or vehicles.”Some simple examplesfollow:
(1) Drivers in Sweden used to have a 92% seat-belt wearing rate. Good but not good enough. EuroNCaP1 established a protocolfor seat-belt reminders a couple of years ago having the effectthat 70% of new cars sold in Sweden 2005 had seat-beltreminders. The drivers of these cars have a seat-belt wearingrate of 99%. Hence, the problem of seat-belt wearing will graduallybe solved at a very low cost.
(2) Alcohol: All over the world alcohol and traffic is a big problem, even if improvements can be made with strict legislationand enforcement. By demonstrating a demand for safetransport primarily by professional transporters a demandfor “proven sober” transports has risen. In Sweden about50% of all school buses have alcohol interlocks (a device thatchecks if the driver is sober). A new generation of Alco locksare coming on the market (at least four competitors in Europe/USA) reducing price and improving performance.
In this way a car that reminds you to use your seat-belt, andchecks your breath for alcohol, or otherwise checks your performance, and assists you to be a better, safer driver. Different aspectsof the Vision Zero philosophy can be found in (Tingvall et al., 1996, 1997; Tingvall, 1998, 2007; Belin et al., 1997).
3. Traditional road design philosophy
The traditional road-oriented safety philosophy has as its startingpoint the ‘‘accident”. Accident statistics are normally based onpolice reports made up on traffic accidents known to the police. These statistics have been used by road authorities world-widefor describing and analysing the road safety problem associatedwith roads and road design. It is important to notice that the conceptsof traffic accidents and (bad) road safety are not synonymous. Many accidents could be an indicator of (bad) safety, but if theaccidents do not lead to personal injuries they are not. Road safetyis a ‘loss of health’ problem. A crash or accident without loss ofhealth is no safety problem, only a cost. But the thesis put forwardin this paper is another, namely that by choosing the ‘‘accident” perspective, you get a safety philosophy that at its best reducesaccidents, not necessarily personal injuries. And, as all modern definitionsof the traffic 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 accidentsare caused by road users. Society’s most fundamental response toaccident prevention has been rules and regulations for road userbehaviour. The purpose of traffic legislation is mainly to simplifythe tasks for road users, making the risk of accident lower. In manycases this works as intended. But if focus is shifted to the effect ofthe traffic regulation on health loss, the pattern is less clear. Examplescould be, for instance, traffic lights and pedestrian crossings. Installing traffic lights typically results in fewer crashes, but moresevere injuries. Pedestrian crossings generally do not lead to a safercrossing for pedestrians; they facilitate crossing a street but provideno safety in themselves.
When it comes to road- and street design the dominant safetystrategy overall has been to increase space for drivers and vehicles. That is, wider lanes, wider roads, straighter roads, larger crossingsetc. The reasoning behind this is straightforward and logical; ifdrivers run off the road, make the road a little bit wider so thereis room for manoeuvring the vehicle back into the lane and keepingthe vehicle on the road; if drivers run off the road in bends, trymaking the road a little bit straighter thereby avoiding accidentsin bends. This strategy has had some success in reducing the numberof accidents, but even the effect on the accident risk has beenquestioned (Hauer, 1999). The strategy to create space for evasive actionhas not been successful in reducing fatalities and other severeinjuries. In fact, everything else considered, this strategy increasesfatalities and other health losses. A wide, strait road has more fatalitiesthan a narrow road with many curves if everything else is thesame. The reason is simple: the most predominant effect of creatingmore space is an increase in driving speed, which means higherlevels of kinetic energy in crashes. Higher energy levels lead tomore severe health losses, all other things being equal. This increasein speed has two reasons; first road administrations normallyset a higher speed limit on roads that are wide andstraight 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 streetsis one of the main contributions to the present global road safetycrisis. The result is an increase, by one or two factors of 10, inthe risks of severe personal injury or fatality, compared to theVision Zero design philosophy described later in this paper. Noother design parameter has an impact of this magnitude. As anexample Swedish 2-lane highways with a speed limit of 110 km/hhad one of the most severe injury pattern recorded ever; out ofthree persons injured on these roads, one was killed. Relativelynew Chinese highways produce more than 1 killed/km/year. Themain difference between the Swedish rural roads and the Chinesehighways is that the latter have a large quantity of vulnerable roadusers, who are ‘‘separated” from motorised vehicles only by the“wideness” of the roads and traffic regulations e.g. pedestriancrossings. It has been shown on the Swedish roads mentionedin the example that the fatalities can be reduced by 85–90% by applying mid- and side barriers. The Chinese highwaysmentioned above could, at least in principle, be rebuilt reducingfatalities with up to 99%.
A note must be made on motorisation and its effect on overallsafety in a country. Sweden has approximately 0.5 cars/inhabitantwhereas China is only in its beginning as a motorised country with0.04 cars/inhabitant. The World Bank has noted that the number ofpersons killed in a country turns from an increasing trend to adecreasing trend when the GNP/capita reaches approximately8000 US$ (Kopits and Kropper, 2003). A hypothesis based on thisdata could be that the change in composition of traffic, that is, the mixture of protected/unprotected road users reaches a criticallimit at that stage of economic development. That is, the separationbetween vehicles and unprotected road users reaches a certain levelwhich has an overall good effect on road safety. It should alsobe noted that this separation in (most) societies is spontaneousand not engineered. It is a function of more and more peoplebecoming motorised (car or bus) and the number of vulnerableroad users decreasing, especially on rural roads. The challenge in adeveloping country is of course to engineer this separation at an earlystage of motorisation.
4. Design principles in Vision Zero
The human tolerance for biomechanical forces is in this perspectivethe starting point for the design of a safe traffic system. This tolerance is a given factor – it cannot be affected to any significantextent. For instance if cars hits pedestrians at 25–30 km/hmost of them survive. However, if the cars instead do 50 km/h, most pedestrians will die.
The trick from an engineering point of view is to design andconstruct a traffic system where this human tolerance is not exceeded. Whereas the general strategy for safe road design fromthe accident perspective was to increase space for drivers and vehicles, the corresponding strategy from a Vision Zero perspective is tomanage kinetic energy in crashes and collisions. It is kinetic energythat kills and injures the road user – not the accident. By managingthe 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 errortolerance was also the intention behind the idea to give driversspace in the traditional safety paradigm. Space would give room forevasive manoeuvres thus avoiding the accident; the problem wasthat it never worked the way it was intended.
The management of kinetic energy in crashes and collisions canbe broken down to the following principle for road and street design; “Integration and Separation”: kinetic energy is managed byintegrating compatible traffic elements and by separating incompatibleones. Here are some boundary values:
1. Vulnerable road users should not be exposed to motorised vehiclesat speeds exceeding 30 km/h.
2. If 1. cannot be satisfied then separate or reduce the vehiclespeed to 30 km/h.
3. Car occupants should not be exposed to other motorised vehiclesat speeds exceeding 50 km/h inword/media/image1.gifcrossings.
4. If 3. cannot be satisfied then separate, or reduce the angle, orreduce the speed to 50 km/h.
5. Car occupants should not be exposed to oncoming traffic (othervehicles of approximately same weight) at speeds exceeding70 km/h or 50 km/h if oncoming vehicles are of considerablydifferent weight.
6. If 5. cannot be satisfied then separate, homogenise weights orreduce speeds to 70 (50) km/h.
7. Car occupants should not be exposed to the road side at speedsexceeding 70 km/h, or 50 km/h if the road side contains trees orother narrow objects .
8. If 7. cannot be satisfied separate or reduce speed to 70 (50) km/h.
视觉零——道路交通安全的一项实施政策
本文的范畴是一个提纲，一般来说，道路安全理念本来就存在于现在道路和道路设计中。追踪这种理念的起源，提出了新的街道道路的设计原则有人会争辩说，在目前的道路设计理念的缺陷。是主要的原因全球道路安全危机，清楚表明其人造的性质。一个由决策过程所构成的简短的描述，导致零视觉在1997年作为瑞典交通安全政策确立。
通过对问题的分析，为寻求解决之道提出建议。这些解决方案基于视觉零中的一些原则。这些措施包括一个用于创建错误容忍的道路系统的新的基本机制，和道路、街道新的设计原则。因此，传统的“怪罪受害者”的质疑和焦点放在了需要专业人士基于这些新的标准所采取的行动。在过去10年在瑞典的死亡人数已经从大约550 /年下降到450 /年。重新设计的道路中央分隔带已经减少了80％在死亡。街道以30公里/小时的设计速度显示出类似的结果。这表明，从视觉零衍生出来的策略是有效的，但还没有大规模实施。
1、过程
自1993年，在瑞典瑞典公路管理局（SRA）的有一个整体的责任道路交通安全。在1996年，这一责任被政府进一步澄清。瑞典已有非常小的部委（人员数）。因此，像SRA的管理部门经常有半政治任务，如发展政策和目标。政策决定、长期目标和总体预算是由政府或议会做出的，而发展是在管理部门做出的。
继1994年秋季瑞典有了一个新选举的交通部长。交通部长宣布，安全将是她的优先事项之一。部长的工作人员就如何使部长能够做出交通安全优先课题和SRA之间展开对话。在1994年春天，SRA和主要利益相关者一起对1994-2000年的行车安全提出了一项短期方案。它不仅有和先前工作的连续性，而且更加强调关键行动和重视成果之间的协作。这个方案后，直接推动SRA开始制定交通安全长期战略的基本思路。它已经被确认为当代一些交通安全问题的范例（约翰逊，1991）。部分问题的原因是许多措施缺乏预期的效益，这被Gerald Wilde等承认（2001年，在Wilde中最好的描述）。详细概述可以在经合组织（1990）中找到。
即使不是所有的崩溃或冲突是可以避免的，非常严重受伤可以在原则上是可以避免的，新的安全模式——视觉零是建立在这一基本思想上的。基本思想是建立预测碰撞事故，将健康损失控制在容忍范围以内的安全体系。
部长和她的工作人员认识到在视觉零的想法和政治背景下工作是可能，迅速采用了这一基本思路，制定了文本（翻译Belin等，1997），1997年在议会上提出这一思路，它被所有的政党接受（Tingvall，1998年）。从那时起议会多次在不同场合重复这一思路。“视觉零”的概念在其他很多领域已经成为了“高度的政治野心”的代名词。2008年，政府对视觉零做了一个自杀决定。
1995年，关于视觉零的许多政治辩论和在1997年议会的决策都集中在这样的一个问题“死亡人数是多少，我们才能接受？当时，瑞典大约有500人死于交通事故中。比较与其他运输方式情况下作出安全水平，（显然是零死亡率的目标），职业安全（每年约50人死亡），电力（每年约5人死亡）。从这个政治分析得出的结论是零死亡率的目标是唯一合理的道路交通目标。在同一时期，SRA及其网路的工作集中在寻找从根本上降低道路交通死亡风险的策略。通常旨在减少一个死亡风险的因素10。下面是个例子。
2、视觉零
1997年，瑞典议会通过了一项关于交通安全条例草案其中有人指出：“视觉零意味着最终没有人在道路交通系统被杀死或严重受伤。”
视觉零点并不意味着导致个人财产损失轻微损失和人身受到轻微伤害的事故必须被消除。上述问题并不认为是道路交通安全方面的一个重要的因素，即使他们能为国家的费用，县议会，市和个人带来巨大收益。相反，重点应放在，导致一人被杀害或严重受伤的这些事件。视觉零还提出了一种道德的方法解决来与公路交通有关的健康问题：
“当在道路交通系统中运行时，人身被致死或受到严重伤害在道德上是不能接受的。
视觉零被认为是道路交通系统设计和运作的一个长期目标。重要的是实现零的视觉做法将改变对道路交通的安全的工作目标；即从减少交通事故伤亡的数量方面制定一个明确的目标：消除交通事故所造成的长期健康损害的风险。这些新的方法使我们从“我们能做些什么？”向“我们必须做些什么？”转变。
视觉零对道路交通安全系统中的道路交通安全作出了新的假定划分，道路交通安全责任应遵循以下底线：
1.该系统的设计者总是对道路安全系统的设计、运作和使用负最终责任，
而对整个系统的安全水平负责。
2.道路使用者使用的责任是使用道路交通系统时，要按照设计师所确定的规则。
3.如果道路使用者不遵守这些规则而缺乏知识，接受或能力，或者如果伤害确实发生，系统设计者必须采取必要的进一步措施，消除人被杀害和受重伤。
采用视觉零方法意味着注重人的生命和健康是设计和运作的道路交通系统绝对的要求。这意味着道路交通安全问题与环境问题相似，必须明确结合影响道路交通安全系统中安全运行的所有进程。基于以下几点：
“人体能够承受的，不能是自身致死和重伤的暴力水平应当是道路运输系统的基本参数。”
基于这个原则，能够发展道路安全的未来社会：通过设计和建造的道路，改良车辆和提高运输服务，使人们受到的暴力水平不超过人体承受范围；这些都是通过不同的支持系统，如有效的贡献规章制度，教育，信息，监测，救援服务，护理和康复。以此为基础，将产生一种积极的需求：寻找新的和有效的解决方案，能够推动公路运输系统的建设重点和要求以及先决条件都在人的需要上。
“这是事实，有95％的事故或碰撞是因为人类的错误，但根据视觉零理念，95％的解决方案在改变道路，街道或车辆。”下面是几个例子：
（1）在瑞典司机曾经有92％的安全带佩戴率。虽然不错，但还是不够好。EuroNCaP几年前建立了一个对安全带提醒协议，结果2005年出售的70%的新车都有安全带提醒装置。这些车的司机安全带佩戴率为99％。因此，系安全带的问题会逐渐以非常低的成本的方式得到解决。
（2）酒精：酒后驾车在世界各地都是一个很大的问题，尽管在严格的立法和执法下，有些改善。证明交通运输的安全性首先要满足交通运输专业人士提出的“证明清醒”的要求。在瑞典约有50％学校巴士有酒精联动锁（一装置检查驱动程序是否清醒）。新一代的酒精锁将要上市（在欧美至少有4个竞争对手），它将有更低的价格和更高的性能。
通过这种方式，一辆车，它提醒你使用安全带，并检查你的呼吸酒精或检查你的表现，并帮助你成为一个更好，更安全驾驶的司机。不同方面的视觉零的理念能在这里找到（Tingvall等，1996年， 1997年；Tingvall，1998年，2007年；Belin等人，1997年）。
3、传统的道路设计理念
传统的道路交通安全导向是以“事故”为出发点。事故统计数通常基于警方报告，而报告是依据警方已知的事故所制作的。这些统计数据已被世界各地的道路部门用于描述和分析与道路安全问题相关的道路及道路设计问题。重要的是要注意的交通事故和（差）的道路安全不是相同含义。很多事故可能是一种（差）的安全指标，但如果事故没有造成人身伤害，则他们（这些事故）不是。道路安全是一个有关人身健康问题。如果碰撞或交通事故没有人身伤害就不是交通安全问题，只是经济损失问题。但在本文中提到另一种安全理念，即从选择“事故”的角度，最大限度的减少事故，降低不必要的人身伤害。正如所有现代交通安全问题都定义为健康问题（健康损失），而从交通事故角度都失去了这个目的。
一般事故分析表明90-95％的事故由道路使用者所造成的。社会对预防交通事故最基本的回应是制定约束道路使用者行为的规章制度。交通立法的目的主要是为了简化对道路使用者的任务，使事故的风险较低。很多情况下这一工作是一目的。但是，如果把焦点转移到交通法规所减少的健康损失的效果上，该模式就不太清楚了。例如，在交通信号等和行人过路处，通常在安装信号灯的地方碰撞事故较少，但多发生严重伤害。行人过路处通常没有行人安全通过的方式，因为他们横穿马路方便，但这给他们自身带来了不安全。
当涉及到以公路和街道为主的安全设计总体战略时是增加司机和车辆的空间。也就是说，更广泛的通道，更广泛的道路，直路，大通道等。这背后的原因是直接的和符合逻辑的。如果司机驾车偏离道路，那么宽一点的路面有助于车辆回到原来道路，继续前行。如果司机驾车在弯道处容易偏离车道，那么就将车道建的直一些，以避免交通事故的发生。这种方法在减少交通事故方面取得一些成功，即使对降低事故风险方面受到质疑（Hauer，1999）。这种方法只是创造了回避的空间，而在减少严重伤亡的方面没有获得成功。事实上，从所有的方便考虑，这一方法增加了死亡和对健康的损害。如果其他一切一样的话，宽阔的道路上比有很多曲线的窄路上有更高的（事故）死亡率。原因很简单：最突出的效果是有更广阔的运行空间，就有更高的车速。这就意味着在车辆碰撞时有更大的动能。在其他条件相同的情况下，更高的能量水平导致更多的健康损伤。车速增长有两个原因：一是道路管理者在宽阔的道路上的规定的车速上限值大，二是在直的道路上，司机被告知这种道路安全等级高，致使司机在这些道路上更快的行车。
建造宽阔、笔直的道路和街道的这种安全理念是导致全球道路安全危机的主要原因之一。通过与后文中的视觉零理念的对比，得到在严重人身伤害或死亡方面的风险会增加，这是由十个因素中的一个或两个引起的。没有其他的设计参数有如此巨大的影响。例如，瑞典二线的公路，最高车速限速我110公里/小时。而在这些道路上有最严重的伤亡记录，一人死亡，超过三人受伤。相对于新中国公路产生的每年每公里公路上死亡超过一人来说。瑞典乡村公路和中国公路主要不同是：后者有大量的易受伤的道路使用者，只能采用像是采用拓宽道路和交通法规的方法使他们与机动车分离。
必须注意机动车化及其对整个国家道路安全的影响。瑞典机动车大约有0.5辆/居民，而中国在开始时机动车为0.04辆/居民。世界银行指出，当国民生产总值/人均达到约8000美元，一个国家的道路死亡人数从原来的上升趋势变为下降趋势（Kopits和Kropper，2003）。基于这些数据，有这样一种假说：交通组成的变化，也就是说，在这个经济发展阶段，受保护/未受保护道路使用者的混合交通达到临界限。也就是说，分离车辆与未受保护道路使用者达到一定水平时，有最佳的道路安全的整体效果。它还应值得注意的是，这（大多数）社会的分离是自发的而不是设计的。还有这样一个功能越来越多的人使用机动车（车或公共汽车）和减少脆弱道路使用者数量，尤其是在农村道路上。这在发展中国家是一个挑战，当然，工程师在机动化的早期阶段的这种分离也是挑战。
4、视觉零的设计原则
交通安全系统设计的出发点从这样的一个角度：人类所能忍受的生物力学方面的暴力。这种忍受能是一个给定的因素—这不会在重大程度上的影响。例如，汽车以25—30公里/小时的车速撞击行人，大部分被撞击者能够幸存。但是，如果汽车以50公里/小时车速撞击行人，则大多数行人会死亡。
鉴于道路安全设计在交通事故方面一般思路是增加驾驶员和车辆的空间，从视觉零角度相应的策略是控制车辆冲突和碰撞时的动能。就是这些动能使道路使用者受到伤亡，而不是事故本身。通过控制碰撞时传递到人体的能量，一种错误的忍受能力将被放入交通系统中。事实上，错误容忍能力观点的背后目的是给驾驶员空间的传统安全模式。有空间来进行回避操作，避免发生事故，但问题是没有按照所计划的方式生效。
控制车辆碰撞冲突时的动能，可以被分解的关于道路和街道设计以下原则：“整合”和“分离”即通过整合兼容的交通要素和分离不兼容的交通要素。这是一些边界值：
1、易受伤害的道路使用者不应该接触机动车时速超过30公里/小时的机动车。
2、如果第1条不能满足，则要将易受伤害的道路使用者和机动车分离或减少车速到30公里/小时。
3、在转弯超过90度路口，车辆内成员不应接触车速超过50公里/小时的其他车辆。
4、如果第3条不能满足，那么要是他们分离或减小角度或降低车速到50公里/小时。
5、车内的人不应该接触迎面而来的车辆（其他车辆大约同等重量）速度超过70公里/小时或车速50公里/小时，如果迎面而来的车辆是相当不同重量。
6、如果第5条布不能满足，那么应该分离车辆或使车辆质量平均或降低车速到70 (50) 公里/小时。
7、车内的人不应该接触路边，在车速超过70公里/小时或车速50公里/小时，路边有树木或其他狭窄物体。
8、如果第7条不能满足，那么应将车辆与路边分离或降低车速到70 (50) 公里/小时。
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