A first principles assessment
Why introduce accident remedial measures?
Which measures should be introduced?
Why introduce speed limitation and enforcement?
Why introduce road marking?
Demand impacts
Short and long run demand responses
Supply impacts
Financing requirements
Expected impact on key policy objectives
Expected impact on problems
Expected winners and losers
Barriers to implementation

Why introduce accident remedial measures?

Traffic accidents create an enormous global health problem.  According to the World Health Organisation report there are more than 1.24 million road deaths worldwide each year, and it is estimated that there are 20 times as many non-fatal road injuries (2013, pp. 4-7).  Risks of death and serious injury on the roads vary greatly within and between countries, and across users of different transport modes, among different income groups, and among different age groups.    

The WHO (2013) reports that young people are especially vulnerable to road traffic deaths, with this being the “leading cause of death for young people aged 15–29 years” (p. 1).   Further the WHO study found that “[h]alf of the world’s road traffic deaths occur among motorcyclists (23%), pedestrians (22%) and cyclists (5%) – i.e. “vulnerable road users.”” (p. 6), and that the ”European Region has the highest inequalities in road traffic fatality rates, with low-income countries having rates nearly three times higher than high-income countries (18.6 per 100 000 population compared to 6.3 per 100 000)” (2013, p. 5).

The size of the health risk posed by road accidents in a country depends on the amount of travel performed per year per inhabitant, the level of traffic risk, and the resources available to protect road users from fatal injury or provide rapid medical treatment of serious injuries. There is a simple definitional relationship between health risk and traffic risk (Elvik & Vaa 2003):

Health risk = Traffic risk x Motorization rate (the number of motor vehicles per inhabitant in a country).

There are fairly large variations in both health risk and traffic risk between motorised countries (having at least 0.14 motor vehicles per inhabitant).

Table 2: Road accident fatalities, health risk and traffic risk in IRTAD member countries. Source: IRTAD (OECD)

Road accident costs have three major components; direct costs (medical treatment, repairing vehicles etc.), indirect costs (losses in output attributable to premature death, permanent impairment or temporary absence from work) and the value of preventing premature death and pain, grief and suffering caused by road accidents. If an economic valuation of lost quality of life is included, the costs amount to 2.5% of GNP (gross national product) on the average, based on estimates for 12 countries. There is substantial variation among countries, with a range from 0.5% to 5.7%. If the costs of lost quality of life are excluded, road accident costs on the average drop to 1.3% of GNP, with a range from 0.3% to 2.8% (Elvik 2000).

Which measures should be introduced?

A whole range of measures is necessary to maintain traffic safety levels, and to increase traffic safety further. The greatest potential for improving road safety is attributable to traffic enforcement (particularly speed limits), motor vehicle safety standards and police enforcement. The benefits of increasing speed enforcement greatly exceed the costs. Improvements to infrastructure can impact on safety, however such improvements can prompt greater risk taking by drivers (Albalate et al. 2013).  Motorways are the safest type of road, but building them is an expensive way of reducing accidents and can have severe detrimental impacts for social equity, particularly exclusion of those without access to motor vehicles, as well as risks of increasing greenhouse gas emissions and poor local air quality by inducing travel demand. ITS-systems cannot improve road safety in the short term, but could contribute in the longer term (15-20 years). Driver training and public education and information campaigns have a much smaller potential for improving road safety (Elvik 1999).

High speeds and great variations in speed increase the probability of accidents and serious personal injuries, since the demands on the road users’ observations and reactions increase, and because braking distance increases proportionally with the square of the speed. Furthermore, the risk of fatal injuries increases by the square of the change in speed to which the body is exposed in an accident. This means that for a given increase in speed, the risk of fatal injury increases even more.  Recent studies support evidence that any reductions in speed (and impact speed) are beneficial in reducing risks of fatality for pedestrians hit by vehicles (Kröyera at al. 2014)

In figure 1 the relationship between changes in the number of accidents and changes in mean speed are presented. Both variables are given as percentage changes.

Figure 1: Relationship between changes in the number of accidents and changes in speed. Percentage. Source: Elvik et al 1997. Copyright ã TOI

A driver may want to get from A to B using as little time as possible and with a reasonable feeling of safety while travelling. Drivers might trade off travel time against safety for themselves and for other road users. In this evaluation, factors such as road geometry, driving and light conditions, the amount of traffic, the characteristics of the car, drivers’ perceptions of their own skills and motives, accident rates and the possibility of police enforcement are all included.

The objective of speed-reducing devices, which make fast driving uncomfortable or impossible, is to get speeds down to a desired level. Speed-reducing devices are intended to force vehicles to keep to low speeds, so that the risk of accidents is reduced and feelings of safety increase.

Respect for the speed limit may vary considerably amongst car drivers. Exceeding the speed limit is probably the most common form of violation of traffic regulations. Many drivers drive faster than the legal speed limit - some much faster. Even though the actual risk of apprehension may be very low, the knowledge that speeds may be checked by the police does affect behaviour. The objective of speed enforcement and enforcement is to maintain and possibly also increase respect for the legal speed limits.

Why introduce road marking?

To drive safely and comfortably, drivers depend on reference points in the proximity of the vehicle and further ahead in the direction they are driving. Road markings are intended to give drivers such reference points. By road marking one can direct traffic by indicating the path of the carriageway, warn road users about specific or hazardous conditions related to the road alignment, control traffic, for example by reserving certain parts of the road for certain road user groups as well as supplement and reinforce information given by means of traffic signs.

It is documented that speed limitation and enforcement will induce increased travel/time costs for vehicles (Elvik et al. 2009). On the other hand, if speed becomes more evenly distributed in areas where traffic is heavy, this may lead to better utilised capacity and reduce time costs for the society at large.  Studies report that in addition to increasing risks to pedestrians and cyclists, high traffic speed can inhibit levels of walking and cycling (Jacobsen et al. 2009; Pucher and Buehler 2008). 

Suspension of the driving licence for speeding will make it necessary for the offender to shift to other transport modes for a period. The impacts for these drivers are not commented on.

Road marking will not have demand impacts of the type discussed below. (Rumble strips, though, will increase noise.) The content in the tables therefore only refers to speed limitation and enforcement.

	= Weakest possible response,		= strongest possible positive response
	= Weakest possible negative response,		= strongest possible negative response

= No response

Short and long run demand responses

It might take some time to adjust to a changed traffic pattern and to change habits to adapt to new speed limitations.

The immediate effects of speed enforcement will be maintained from 2 days to 10 weeks (Elvik et al 1997), but will also hopefully lead to increased respect of legal speed in general.

	= Weakest possible response,		= strongest possible positive response
	= Weakest possible negative response,		= strongest possible negative response

= No response

Supply impacts

Speed limitation and enforcement will not influence the road space at hand or its capacity. Road marking aimed at reserving certain parts of the road for certain traffic groups, will alter the supply between different road users.

The throughput of a road is at its highest if a speed of around 60 km/h is enforced. If in addition such speed enforcements induce more evenly distributed individual speeds, the throughput is increased further.

The costs of speed limitation and roadmarking depend on the measures used and the amount of traffic on the road.  Police enforcement is more expensive, but the benefits largely exceed the costs, and this ratio may increase when wider social benefits including health and social inclusion are considered. 

Expected impact on key policy objectives

Road markings have no impacts on other key policy objectives other than safety. Their impacts depend on the type of road marking, cf. Evidence of performance. The comments below refer to speed limitation and enforcement.

The impact on environment is a complex issue, since lower speed has different impacts on noise and pollution, as well as on various type of pollution, cf. Evidence on performance.

	= Weakest possible positive contribution,		= strongest possible positive contribution
	= Weakest possible negative contribution		= strongest possible negative contribution

= No contribution

Expected impact on problems

For many problems speed reduction can have both positive and negative effects.

Problem	Scale of contribution	Comment
Congestion-related delay	/	Lower speeds induce individual delays and congestion, but if speed becomes more evenly distributed, this may mean that the capacity is better utilised when traffic is heavy. If walking and cycling increase as a result of lower speed, this can reduce congestion
Community impacts		By making it easier, less dangerous to cross roads for pedestrians and cyclists. Reduced severance and increased liveability
Environmental damage	/	Speed reduction at high speeds will reduce energy consumption and CO2, but at lower speeds the effect is opposite. However if lower speed encourage walking and cycling this will benefit the environment. Lower speed will reduce recirculation of dust particles. No evident positive effect on other local pollutants. If increased congestion with uneven (transient) driving, local emissions will also increase. However if lower speed encourage walking and cycling this will benefit the environment
Poor accessibility		Lower vehicle speed in living areas will make travelling easier for pedestrians and cyclists, many of whom are children, older people and not car-owners
Disproportionate disadvantaging of particular social or geographic groups		See above
Number, severity and risk of accidents		Reducing speed will reduce accident risk and the severity of accidents substantially
Suppression of the potential for economic activity in the area		There may be economic benefits from congestion reduction if road traffic decreases and walking and cycling increase. Reducing the high mortality burden that road traffic places on young and economically active adults may support economic development (see WHO 2013)

	= Weakest possible positive contribution,		= strongest possible positive contribution
	= Weakest possible negative contribution		= strongest possible negative contribution

= No contribution

Expected winners and losers

Group	Winners / losers	Comment
Large scale freight and commercial traffic		More evenly distributed speed and better capacity on highways will give advantages to commercial traffic.
Small businesses		More evenly distributed speed and better capacity on highways will give advantages to commercial traffic.
High income car-users		On the average accident reductions outweigh time losses.
People with a low income		Given better conditions for pedestrians and cyclists.
People with poor access to public transport		At specific spots, easier crossing for pedestrians might increase access to public transport stations.
All existing public transport users		-
People living adjacent to the area targeted	/	Better conditions for pedestrians and cyclists are positive effects, but possible congestion is a negative one.
Cyclists including children		Lower speed reduces risk of death and serious injury to cyclists. By improving perceptions of safety, it might increase cycling bring health benefits of active travel and social inclusion and economic inclusion for those withuot vehicles.
People at higher risk of health problems exacerbated by poor air quality	/	Lower speed will reduce recirculation of dust particles. No evident positive effect on other local pollutants. If increased congestion with uneven (transient) driving, local emissions will also increase. However if lower speeds encourage mode shift to walking and cycling this will benefit air quality.
People making high value, important journeys	/	Depends on the route necessary. Individual delays will affect this group more than the average car user, but so will more even speed on highways and fewer accidents.
The average car user	/	Individual delays will be a negative impact, (as will suspension of drivers licence), but more even speed on highways and fewer accidents will be positive ones.

	= weakest possible benefit,		= strongest benefit
	= weakest possible disbenefet,		= strongest possible disbenefit

= neither wins nor loses

Speed limitation and especially speed enforcement encounter great barriers to implementation due to the strong position of car owners and car organisations in the political process.

Barrier	Scale	Comment
Legal		None.
Finance		Finance is required to implement measures however this is offset by economic savings from accident reduction and from benefits of mode change.
Governance	/	There may be no barrier although co-ordination between different levels of government and different public services and enforcement agencies may be required.
Political acceptability	/	Political acceptability can echo aspects of (perceived) voter acceptability.
Public and stakeholder acceptability	/	There can be opposition from some drivers, however there is broad support from accident prevention and health organisations, and from environmental, and social justice groups and residents.
Technical feasibility		None.

= minimal barrier,

= most significant barrier