So your civilization kills 1.35 million people per year in automobile-related crashes. This is a tragedy, but it is no “accident“. Road deaths are largely preventable, and the evidence is that some countries (the United States, Australia) have much higher rates of road death than others (Sweden). The strategies to reduce the carnage go under different names in different places, from Vision Zero to the Safe Systems Approach, but they are not really that distinct substantively.

Most crashes have multiple points of failure in the chain of causation. If only party A was paying more attention, it wouldn’t matter what party B was doing, and vice versa. If the road were designed differently, party A would have behaved differently.

Consider a vehicle-on-vehicle collision. There are at least six actors here: The driver, the other driver, the vehicle, the other vehicle, the road, the environment. Other vehicles (and their drivers) may also have a role to play, even if they are not directly involved in the crash.

The penalty for distraction or misjudgment should not be death. No one deserves to die for a momentary lapse of awareness. Driving is a hard skill, people are fallible, and in addition to the road deaths noted at the beginning of this post, there are hundreds of millions of severe crashes each year globally, many of which are injurious and life-changing, even if not life-ending.

The general approach is two-fold:

• Prevent crashes.
• Mitigate crash consequences: prevent death and reduce injury.

The good news is that the same things that prevent crashes often reduce the severity of crashes should they occur. Going slower gives drivers more time to react, but even if they fail to reach in time, (braking too late, or not at all), they still are less likely to be killed or injured, or kill or injure others, at a slow speed than a fast one.

The problem is that drivers often do not want to go slower, and the feeling is that the behaviour which is safer is also less efficient. This is true assuming no crash. Of course, being involved in a crash, or stuck in the congestion behind someone else’s is not efficient either.

The safety advocacy field has long used the 3 Es of Engineering, Enforcement, and Education to describe their strategies. This has been extended with other Es, including variously Emergency Services, Evaluation, Environment, Encouragement, and Everyone Else. Toole Design: has recently proposed a new set of 3Es: Equity, Ethics, Empathy. The Es are a useful mnemonic, but we need to dig deeper. This post includes 21 strategies that improve safety.  You might think of others. There is no one magic bullet for this complex problem, though some strategies are more effective than others depending on context.

Engineer for Safety

Design the system to be safer.

Foremost, this means design for slow speed. Wherever a pedestrian may come into conflict with a vehicle, the speed should be as low as possible, but start with 30 km/h (18 mph) as at that speed pedestrians are more likely to survive being hit by a car than die, while at higher speeds the reverse is true. If vehicles must go faster, the separation of pedestrians, bicyclists, and cars should be considered. There are numerous strategies to achieve low speeds on streets, including regulations (discussed below), enforcement of those regulations, and better, designing roads so that drivers only feel comfortable driving at low speeds.  There are numerous techniques to reduce the design speed of streets and roads, including traffic calming devices and shared space approaches.  Traffic calming aims to use street designs to reduce speed, by making it difficult or uncomfortable to travel faster. Solutions include narrowing the street, chicanes to alter direction of vehicles, and speed tables and wombats (raised pedestrian crossings, at intersections or midblock) to remind drivers they are in pedestrian areas. Shared spaces allow persons in and out of vehicles to use the same area and visually negotiate conflicts rather than requiring on an excess of signs, signals, and markings regulating behaviour. The Netherlands has probably done the most to improve the streetscape for the benefit of safety following the “stop the child murders” (Stop de kindermoord) campaign of the 1970s.

Use of roundabouts rather than traffic signals takes up more space, and increases the distance pedestrians have to walk, but by lowering speed at the intersection and deflecting cars, generally results in an overall safer situation than a signal or stop-controlled intersection. In addition to being safer, lower speeds also make driving less advantageous compared to other modes, and reduces demand for cars, which likely improves safety as well.

But it also means that designs for high-speed roads should be safer through better geometric design. Geometric design is usually about the design of horizontal and vertical curves, and the visibility at those curves determines the appropriate speed (or the design speed determines the curvature), which depends on driver perception and reaction times.  But there are other aspects as well.  Civil Engineers are responsible for designing roads and the traffic controls (signs, signals, and markings) that govern them. As an undergraduate student at Georgia Tech, my Transportation Engineering Professor, Paul Wright, was very much concerned with traffic safety. One of the problems he identified was that cars ran off the road at high speed and hit fixed objects, like light poles, or trees, which killed the driver or passenger, while the pole or tree remained standing. So he advocated ensuring the side of state highways were clear of fixed objects within 30 feet (~8 m) of the road edge. Light poles and signs would be redesigned to be breakaway, instead of being designed to outlast a car crash. Trees would be cut down. Bridges would have protected guardrails so that cars would be deflected back into the stream of traffic rather than crashing into a concrete pillar (as bridge pillars should not be breakaway for obvious reasons).  This apparently reduced deaths, though was unfortunately also applied in urban areas, encouraging higher rates of speed. Other similar strategies include cables in the medians of highways to reduce cross-over crashes (which are far worse as the speed of impact of a head-on crash is so high).

Different types of roads require different treatments. Limited access motorways (freeways) are generally safer at high speeds than city streets, and when faster (e.g. with higher freeway speed limits, to a point), attract traffic away from city streets and rural roads, which reduces overall statewide fatalities, though increases them on the relevant freeways, and probably induces increased demand overall.

Design road surfaces to reduce slip and increase friction. Pavement engineers consider not only the strength of pavements, but their surface condition.

Maintain Roads to improve traffic safety as well. This includes the general road condition, as well as snow and ice clearance. Toshihiro Yokoo, Mihai Marasteanu, and I found that good pavement quality is associated with lower crash rates in several conditions:

• Snow – for fatal crashes,
• Asphalt over concrete and sags for injury and property damage crashes,
• Wet roads for injury crashes, and
• Crests, and spring load restrictions for property damage crashes.

It should also be noted that very bad pavement quality also performs as a type of traffic calming, as people are uncomfortable traveling at higher speeds on bumpy roads.

Educate, Enforce, and Regulate Drivers

Regulate driver behavior by adopting severe rules about drunk driving (drink driving, driving under the influence, driving while intoxicated) and rules about maximum hours to ensure drivers are as alert (sober) as possible when making decisions. In a sense much of this is pre-crime, we regulate this behavior even if the driver has not actually driven badly or caused a crash because they are in a state where they might at a moment’s notice. But unlike walking, driving is a privilege, not a right. Other rules include things like prohibiting the use of mobile phones while driving, as distracted driving, unlike distracted walking, is a real problem. Some rules are downright counterproductive, like assuming pedestrians should only cross at marked crosswalks. The US is terribly inconsistent about which crosswalks are marked, leading to confusion and danger.

Enforce the adopted rules and laws like the speed limit and other traffic laws that improve actual safety (that is, punish bad behavior). This is traditionally the responsibility of the police. Much of this can be automated with various types of `photocop‘ technologies, such as red-light running cameras and photo-radar speed enforcement. These generally improve safety. In contrast, ad hoc human-based enforcement often has racial bias, and has traditionally been used as a pretext to harass minorities. Still, if people believed there were serious consequences for violating road rules and killing or injuring other people with automobiles, they would probably be more careful.

Encourage and reinforce good behavior. While encouragement is not widely used, it is certainly possible to imagine earning points for good behavior, that might result in lower insurance premiums, or removing points from your driver’s license. However encouragement has its downsides:  imagine being pulled over by police, even if in the end they give you a citation of good behavior, the stress of the event, depending on your circumstances, especially if you had a record or points, may have taken several hours or days off your life)

Educate and License drivers, both new and continuing, on the state of the road rules, and their knowledge thereof. Driver education (and examination and licensure) is intended to produce better drivers. The US driver education system is not especially rigorous given the damage that can be caused, and there is no effective “continuing education” for drivers, requiring them to demonstrate continued improvement in driving skills, aside from occasional public service announcements and variable message signs. Practice improves skill, but experience creates relaxation and may induce over-confidence on the job (of driving). Licensure has been getting more rigorous in the US, and this has improved safety. Still, the only rigorous test are for the first time the license  is earned, and changes in road rules are never tested, much less memory of the existing road rules.

Equipment

Equip vehicles with technologies that reduce injury to vehicle occupants in a crash, and equipment that reduces the likelihood of a crash in the first place.

Mechanical engineers have done better at the first of these, vehicle occupants are much less likely to die due to better-designed automobiles that now feature things like:

• Seatbelts
• Crash cages
• Crumple zones
• Shatterproof Glass
• Airbags
• Child safety seats (car seats)

Software and electrical engineers have helped develop systems such as

• Rear cameras, for backing up,
• Lane-departure warning
• Automatic emergency braking systems
• Adaptive cruise control
• Auto-pilot, Supercruise, other advanced driver assistance systems

which improve safety, the latter ones especially on highways.

However, the increase in SUVs increases the severity of crash consequences for those outside the vehicle (in other cars, or on foot or on bike) both due to the mass of the vehicle, and the height, which collides with the soft body of the pedestrian nearer the vital organs than a lower sedan.

Materials engineers and mechanical engineers are involved in the design of tires, which is an important element in safety.

Equip humans with safety gear. If we can redesign vehicles, can we also redesign our unprotected road users, pedestrians and bicyclists?  Safety promotors have essentially proposed this. Some equipment that helps pedestrians and bicyclists be seen is that which increases visibility, including bicycle lights and increased reflectivity of the bicycle or the high-visibility clothes worn by road users. Or worse, asking pedestrians to carry flags to cross the street. By increasing visibility, the argument goes, the driver will be able to react and apply the brakes sooner, and either stop, or at least be slower, at the time of impact. The empirical evidence for safety is non-existent either way on reflective gear, though one imagines it helps, as it improves visibility in tests.

Vehicle equipment designs that reduce the impact of vehicles on bikes and people on foot should also be considered. The increasing height and mass of SUVs (and their increasing number) has been credited with the fast-rising number of pedestrian deaths in the US in recent years. The height makes it harder for drivers to see people (especially children and others who don’t play basketball professionally) just in front of the vehicle. The height also means the collision will occur on the upper rather than lower half of the body, where people keep most of their vital organs.

Bicyclists are often asked or required to wear helmets in countries like Australia with a weak biking culture. Yet the safest countries for bicyclists, like the Netherlands, don’t require this. It is clear from the medical literature that if you are dropped on your head, a helmet helps. But that is not the whole story. The question is one of incidence, whether a helmet increases the likelihood of being dropped on your head, either because of more aggressive cars around helmeted, uniformed, and armored bicyclists or because of the false confidence that helmets provide bicyclists. By the same logic, vehicle passengers and drivers should wear helmets and goggles, which will reduce injury and death. We might want them wearing giant inflatable bags as well. This seems ridiculous, but we essentially ask this of bicyclists. The entire conception of bicycling as a race requiring special gear ensures we have othered (dehumanized) the bicyclist, which reduces driver empathy. Delbosc et al. have found that dehumanization is correlated with aggression.

Ergonomics, or Human Factors Engineering,  considers road user interaction with the vehicle and with the road environment. Out-of-vehicle, human factors engineers are responsible for standardising traffic signs, signals, and markings, and interfaces, which appear to be getting better, if too numerous. In-vehicle, human factors engineers interfaces like the dashboard, which appears to be getting worse, increasing the distractability of drivers.

Emergency Response

Emergency response saves lives if there is a crash, and this has been getting better, both in terms of reduced response time, due to almost instant notification of an incident from vehicle-based systems or from mobile phones, as well as faster dispatching of emergency response, as well as improvement in medical care technologies over the past century. Improvements in response time and medicine are responsible for about one-third of the reduction in fatality rates from crashes in the UK.

Exposure

Fewer automobiles will result in fewer automobile-related deaths. No cars eliminate the risk entirely, but also is beyond the pale to consider, apparently.

Pedestrianisation, or reducing the number of roads where cars are permitted, naturally reduces car crashes on the pedestrianised sections. Similarly, better pedestrian networks and pedestrian priority will both increase pedestrian safety and reduce the number of drivers. A key example of this is the trip to and from school, which children used to do on their own

Improve public transport, walking, and bicycle networks, to reduce the number of people who feel the need to drive.

Change land use patterns to reduce driving. Reorganizing the location of activities so that origins and destinations are nearer means more trips can be by walking, biking, or public transport. Denser areas are generally safer on a per capita basis (that is the more people, the more collisions, but the rate of serious collisions per pedestrian or per vehicle drops), as there are safety-in-number effects, which we have corroborated for pedestrians and bicyclists. The relationships are complex.

Grid the street network. Marshall found that “Denser street networks with higher intersection counts per area are associated with fewer crashes across all severity levels.”

Economy is a factor, the better the economy, the more people driving, both to work and to non-work destinations. Our research has shown that as the gas prices rise (and one expects, as the economy deteriorates), the drivers who give up the road are typically worse than average, often younger, less responsible, and less able to hold down a job, while younger potential drivers defer licensure. It might be socially counter-productive to want high gas prices or a bad economy solely to reduce road deaths, and a bad economy may very well increase other deaths, though high gas prices may have additional beneficial effects from reduced pollution. Nevertheless, the correlation remains.

Emerging Technologies

Vehicle automation will certainly help in the long run, as computers are less likely to be vulnerable to the same imperfections that humans suffer when attempting to maintain concentration, and are programmable to behave in a more risk-averse way, as well as having faster reaction times and being more predictable and more likely to obey road rules. But we are at least two decades away from full automation, and many of the strategies here will help even with automated vehicles.

Conclusions

Like congestion and global warming, the road death toll can be significantly reduced, but there is little evidence that the United States, in particular, is collectively interested in solving it. While there are obviously advocates, they do not have the upper hand, otherwise deaths would not be rising in recent years off its 2014 lows.

Ezra Hauer argues convincingly that practice needs to engage better with research, and be more evidence-based. There are other strategies as well would result in safer systems that kill and injure fewer people each year.  Despite the high road toll, the issue seldom received the attention it deserves, overshadowed by more newsworthy types of death. This post also doesn’t cover the deaths due to air pollution, which is of a similar magnitude, and suggests another set of solutions.