## 3. Road safety performance indicators

Installation of no passing zone through delineation	40
Lighting of at grade intersections (over- all)	30
Lighting of at grade intersections (night)	50
Installation of right-turning lanes	35
Installation of rumble strips	25
Improvement of road surface	25
Installation of crash barrier (fatal acci- dents)	65
Sight distance improvements	30
Improvement of horizontal alignment	40
Construct grade-separated interchange	55

Road safety can be assessed in terms of accident frequency and resultant costs but simply counting crashes or injuries can produce an imperfect indication of the level of road safety. For example, the under reporting of traffic accidents, as high as 50% for minor accidents and 25% for serious injury accidents in Ireland [2], can produce an apparent change in the number of reported accidents. Accident counts need to be supplemented by other meas- urements that are causally related to crashes or injuries in order to indicate performance [10]. These additional meas- urements are referred to as safety performance indicators. Regular monitoring of such performance indicators can improve the understanding of road accident trends by providing a more complete picture of the level of road safety and by pointing to the emergence of new problems at an early stage. Some EU member states have shown that safety performance indicators can be used efficiently for monitor- ing the progress of road safety policies in meeting their de- sired targets and for permitting interventions where neces- sary [10]. The most commonly used safety performance indicators for road transport in Europe include speed meas- urement, seat belt and crash helmet usage and drink driving incidence. Table 3 suggests performance indicators for the evaluation of Irish road safety. It should be noted that these performance indicators require further refinement.

######### 2.2. Enforcement countermeasures

Enforcement has been shown to significantly reduce traffic accidents. Research in Ireland indicates that a 1% increase in the number of hours spent on police surveillance could yield a 2.6% reduction in the number of serious injury accidents [5]. The European Transit Safety Council estimates that 50% of traffic accidents could be avoided if road users complied completely with road traffic regulations [1]. If traffic viola- tions were eliminated, it has been estimated that fatalities could be reduced by as much as 63% [6]. Three specific violations contribute considerably to accident fatalities, speeding, drink driving and seat belt use [7]. Excessive speed is by far the most prevalent traffic offence [1]. A considerable reduction in fatalities resulted from the introduction of penalty points for speeding in Ireland in late 2002. Unfortunately, this effect has since diminished due to a lack of enforcement. A number of studies have investigated the impact of enforcement on traffic accidents including the use of fixed and mobile speed cameras. Table 2 summarises the researched effects of both manual and automated speed enforcement. Effects of manual and automatic speed en- Table 2. forcement.

## 4. Linear programming model

One of the central components of the road safety manage- ment process is the allocation of resources. It is suggested that linear programming can be used to optimise the road safety countermeasures. The objective of this model is to provide a system of road safety management whereby dif- ferent road safety measures/strategies (inputs) are analysed and the resultant effects (outputs) are quantitatively esti- mated.

Effect	Manual enforce- ment	Automatic enforcement
% Reduction in ac- cident frequency	2 – 4	20 – 24
% Reduction in no. KSI* accidents	14 – 58	17 – 38
% Reduction in mean speed	3.6 – 4.5	4
Average speed re- duction (km/h)	3.6	2.9 – 6.9
Distance halo (km)	1.6 – 3.5	1 – 10
Time halo (days)	1 – 63	not applicable

######### 4.1. Scope of the model

The safety situation on a specific route is first quantified. The level of safety achieved through the implementation of se- lected engineering and/or enforcement road safety interven- tions is then estimated. The output generated by the model represents the expected magnitude of road safety in terms of accident severity and cost. Ideally, the model should also indicate if the proposed road safety measures are cost effec- tive.

####### *KSI = Killed and Seriously Injured.

######### 4.2. Formulation of the model

######### 2.3. Education countermeasures

The model operates on the basis of estimating the effec- tiveness of the selected input variables (road safety measures). The effectiveness estimation apportions the ex- pected accident reduction benefits to the road safety measures. These benefits are correlated with performance

Education including driver training is considered an essential component of road safety management and advertising forms part of most road safety campaigns. However, it has proved difficult to apportion accident reduction figures to education countermeasures.