road traffic safety road traffic safety road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. typical road users include pedestrians, cyclists, motorists, vehicle passengers, horse riders, and passengers of on-road public transport (mainly buses and trams). sidewalks, curbs and traffic signals in hagerstown, maryland, united states speed limits in different areas, unusually with only a "recommended" limit (130 km/h) for the autobahn drip variable message sign guiding traffic on the dutch a13 motorway vehicles experiencing a breakdown or an emergency can stop in the emergency lane; these lanes may themselves present risks to traffic. sacrifices to the modern moloch, a 1922 cartoon published in the new york times, criticizing the apparent acceptance by society of increasing automobile-related fatalities best practices in modern road safety strategy: the basic strategy of a safe system approach is to ensure that in the event of a crash, the impact energies remain below the threshold likely to produce either death or serious injury. this threshold will vary from crash scenario to crash scenario, depending upon the level of protection offered to the road users involved. for example, the chances of survival for an unprotected pedestrian hit by a vehicle diminish rapidly at speeds greater than 30 km/h, whereas for a properly restrained motor vehicle occupant the critical impact speed is 50 km/h (for side impact crashes) and 70 km/h (for head-on crashes).— international transport forum, towards zero, ambitious road safety targets and the safe system approach, executive summary page 19 as sustainable solutions for classes of road safety have not been identified, particularly low-traffic rural and remote roads, a hierarchy of control should be applied, similar to classifications used to improve occupational safety and health. at the highest level is sustainable prevention of serious injury and death crashes, with sustainable requiring all key result areas to be considered. at the second level is real-time risk reduction, which involves providing users at severe risk with a specific warning to enable them to take mitigating action. the third level is about reducing the crash risk which involves applying the road-design standards and guidelines (such as from aashto), improving driver behavior and enforcement. traffic safety has been studied as a science for more than 75 years. background guardrails save a vehicle from a long fall c. 1920; but so said the original caption, guard rails were only sometimes effective at the time. it was not until the 1960s that safety testing ensured adequate protection, and even then only for vehicles of a limited weight-class. road traffic crashes have become one of the world's largest public-health and injury-prevention problems. the issue is all the more acute because the victims are overwhelmingly healthy before their crashes. according to the world health organization (who), more than 1 million people are killed on the world's roads each year. a report published by the who in 2004 estimated that some 1.2 million people were killed and 50 million injured in traffic collisions on the roads around the world each year and that traffic accidents were the leading cause of death among children 10–19 years of age. the report also noted that the problem was most severe in developing countries and that simple prevention-measures could halve the number of deaths. the standard measures used in assessing road safety interventions are fatalities and killed-or-seriously-injured (ksi) rates, usually expressed per billion (109) passenger kilometres. countries using older road-safety paradigms replace ksi rates with crash rates – for example, crashes per million vehicle-miles. vehicle speed within the human tolerances for avoiding serious injury and death is a key goal of modern road-design, because impact speed affects the severity of injury both to vehicle occupants and to pedestrians. for occupants, joksch (1993) found the probability of death for drivers in multi-vehicle collisions increased as the fourth power of impact speed (often referred to by the mathematical term δv ("delta v"), meaning change in velocity). injuries are caused by sudden, severe acceleration (or deceleration); this is difficult to measure. however, crash reconstruction techniques can estimate vehicle speeds before a crash. therefore, the change in speed is used as a surrogate for acceleration. this enabled the swedish road administration to identify the ksi risk curves using actual crash-reconstruction data which led to the human tolerances for serious injury and death referenced above. interventions are generally much easier to identify in the modern road-safety paradigm, which focusses on the human tolerances for serious injury and death. for example, the elimination of head-on ksi crashes simply required the installation of an appropriate median crash-barrier. also, roundabouts, often with speed-reducing approaches, feature very few ksi crashes. the old road-safety paradigm of purely crash risk is a far more complex matter. contributing factors to highway crashes may be related to the driver (such as driver error, illness, or fatigue), the vehicle (brake, steering, or throttle failures), or the road itself (lack of sight distance, poor roadside clear- zones, etc.). interventions may seek to reduce or compensate for these factors, or to reduce the severity of crashes. a comprehensive outline of interventions areas can be seen in management systems for road safety. study conducted in finland revealed that the fatality risk is increased most when a collision type is either pedestrian or meeting of the vehicles. in addition to management systems, which apply predominantly to networks in built-up areas, another class of interventions relates to the design of roadway networks for new districts. such interventions explore the configurations of a network that will inherently reduce the probability of collisions. interventions for the prevention of road traffic injuries are often evaluated; the cochrane library has published a wide variety of reviews of interventions for the prevention of road-traffic injuries. for the purposes of road-traffic safety it can be helpful to classify roads into three usages: built-up urban streets with slower speeds, greater densities, and more diversity among road users non built-up rural roads with higher speeds major highways (motorways/ interstates/ freeways/ autobahns, etc.) reserved for motor-vehicles, and which are often designed to minimize and attenuate crashes most injuries occur on urban streets but most fatalities on rural roads, while motorways are the safest in relation to distance traveled. for example, in 2013, german autobahns carried 31% of motorized road traffic (in travel-kilometres) while accounting for 13% of germany's traffic deaths. the autobahn fatality-rate of 1.9 deaths per billion-travel-kilometres compared favorably with the 4.7 rate on urban streets and 6.6 rate on rural roads. road class injury crashes fatalities injury rate fatality rate fatalities per 1000 injury crashes autobahn 18,452 428 82 1.9 23.2 rural 73,003 1,934 249 6.6 26.5 urban 199,650 977 958 4.7 4.9 total, average 291,105 3,399 401 4.6 11.6 per 1,000,000,000 travel-kilometres history roadways originally carried all sorts of traffic indiscriminately - beasts of burden as well as pedestrians. road behavior and rules have developed to prioritize certain types of traffic. important people traversing crowded streets and alleys in ancient rome (famous for its roman roads) deployed minions to clear the way for their litters or (if allowed) carts and chariots. even the mighty preferred not to trample the bystanders. in the 19th century the advent of powered vehicles inspired british road-safety law to impose speed limits and to require a person on foot carrying a red flag warning of the arrival of a frightening noisy mechanical contrivance. subsequently, motoring lobby-groups pressed for the priority of motorized traffic, and safety laws drove playing children off the streets and ghettoized the likes of walkers, bicycles, wheel-chairs and scooters to the margins. concepts like shared space, living streets and woonerven developed to counter this paradigm. mortality mortality units according to the who/irtad: traffic accident data are often compared between countries and between regions. these comparisons are done in numbers of casualties, but also in relation to the number of inhabitants (a measure of national health risk), the number of vehicle kilometres driven (a measure of the transport risk) as well as the number of cars in a country, etc. for a reliable comparison the real volumes should be used (rather than recorded numbers with different recording rates) mortality statistics killed eu28, 2013 killed eu27, 2019 killed japan, 2017 killed us eu source: european institutions (ec): eu28 2013; eu27 2019 japan source: white paper on traffic safety in japan 2018 us source: oecd us source, 2019: nhtsa global mortality by region per million inhabitant in 2015 source: world health organization, global status report on road safety 2015 us mortality by state per million inhabitant in 2013 source citylab: europe mortality in selected countries per million inhabitant in 2013 source eurostat (trans_r_acci serie) (data provided by member countries on a voluntary basis) fatalities by billion traveled km fatalities by billion traveled km fatalities by vmt allow to compare different class of roads, here in france source: maille france: soes, 49e rapport de la commission des comptes des transports de la nation / la documentation française. setra, ministère des transports built-up areas pedestrian crossing, line markings and street furniture a curb extension at a mid-block crosswalk a traffic circle applied to a four-way intersection as a means of improving its safety. this device, with a proven record of collision reductions and traffic flow improvement, turns the cross-intersection into four virtual three-way intersections. utrecht has specially painted bicycle-only lanes. on neighborhood roads where many vulnerable road users, such as pedestrians and bicyclists can be found, traffic calming can be a tool for road safety. though not strictly a traffic calming measure, mini-traffic circles implanted in normal intersections of neighbourhood streets have been shown to reduce collisions at intersections dramatically (see picture). shared space schemes, which rely on human instincts and interactions, such as eye contact, for their effectiveness, and are characterised by the removal of traditional traffic signals and signs, and even by the removal of the distinction between carriageway (roadway) and footway (sidewalk), are also becoming increasingly popular. both approaches can be shown to be effective. for planned neighbourhoods, studies recommend new network configurations, such as the fused grid or 3-way offset. these layout models organize a neighbourhood area as a zone of no cut-through traffic by means of loops or dead-end streets. they also ensure that pedestrians and bicycles have a distinct advantage by introducing exclusive shortcuts by path connections through blocks and parks. such a principle of organization is referred to as "filtered permeability" implying a preferential treatment of active modes of transport. these new patterns, which are recommended for laying out neighbourhoods, are based on analyses of collision data of large regional districts and over extended periods. they show that four-way intersections combined with cut-through traffic are the most significant contributors to increased collisions. modern safety barriers are designed to absorb impact energy and minimize the risk to the occupants of cars and bystanders. for example, most side rails are now anchored to the ground, so that they cannot skewer a passenger compartment. most light poles are designed to break at the base rather than violently stop a car that hits them. some road fixtures such as signs and fire hydrants are designed to collapse on impact. authorities have removed trees in the vicinity of roads; while the idea of "dangerous trees" has attracted a certain amount of skepticism, unforgiving objects such as trees can cause severe damage and injury to errant road users. safety barriers can provide some combination of physical protection and visual protection depending on their environment. physical protection is important for protecting sensitive building and pedestrian areas. visual protection is necessary to alert drivers to changes in road patterns. most roads are cambered (crowned), that is, made so that they have rounded surfaces, to reduce standing water and ice, primarily to prevent frost damage but also increasing traction in poor weather. some sections of road are now surfaced with porous bitumen to enhance drainage; this is particularly done on bends. these are just a few elements of highway engineering. as well as that, there are often grooves cut into the surface of cement highways to channel water away, and rumble strips at the edges of highways to rouse inattentive drivers with the loud noise they make when driven over. in some cases, there are raised markers between lanes to reinforce the lane boundaries; these are often reflective. in