M ODELO L ÓGICO DE D ATOS N ORMALIZADO

1.0 I

NTRODUCTION AND OVERVIEW OF

20

MEASURES

This chapter describes the effects of 20 measures based on road design and road equipment. These 20 measures are as follows:

1.1 Cycle lanes and tracks 1.2 Motorways

1.3 Bypasses

1.4 Urban arterial roads 1.5 Channelisation of junctions 1.6 Roundabouts

1.7 Redesigning junctions

1.8 Staggered junctions (reconfiguring crossroads to two T-junctions) 1.9 Grade-separated junctions

1.10 Black spot treatment 1.11 Cross-section improvements 1.12 Roadside safety treatment

1.13 Improving road alignment and sight distance 1.14 Reconstruction and rehabilitation of roads 1.15 Guardrails and crash cushions

1.16 Game accident measures 1.17 Horizontal curve treatments 1.18 Road lighting

1.19 Improving tunnel safety 1.20 Roadside rest and service areas

The Handbook of Road Safety Measures

Copyright r 2009 by Emerald Group Publishing Limited All rights of reproduction in any form reserved

ISBN: 978-1-84855-250-0

The main features of current knowledge of the effects of these measures on accidents, mobility and the environment are described in this introductory chapter. Emphasis is placed on describing the effects on accidents. The effects on mobility and environ-mental conditions are described more briefly. Costs and salient points of cost–benefit analyses are described as well.

Amount and quality of research

Table 1.0.1 shows the number of studies, the number of results and the sum of the statistical weights of the studies retrieved on the effects of road design and road

Table 1.0.1: The amount of research evaluating the effects on accidents of road design and road equipment

1.1 Cycle lanes and tracks 46 257 18,536 2009

1.2 Motorways 13 55 15,463 1997

1.3 Bypasses 8 73 2,271 2001

1.4 Urban arterial roads 12 86 7,844 2001

1.5 Channelisation of junctions 39 210 7,531 2007

1.6 Roundabouts 39 141 7,692 2009

1.7 Redesigning junctions 11 56 2,618 2008

1.8 Staggered junctions 9 79 1,929 1997

1.9 Grade-separated junctions 20 150 24,751 2006

1.10 Black spot treatment 53 341 55,757 2009

1.11 Cross-section improvements 66¹ 908 168,093 2007

1.12 Roadside safety treatment 6 61 19,643 1997

1.13 Improving road alignment and sight distance

27² 790 30,0024 2007

1.14 Reconstruction and rehabilitation of roads

11 93 6,484 2008

1.15 Guard rails and crash cushions 38 250 27,668 2001

1.16 Game accident measures 25 59 838 2008

1.17 Horizontal curve treatments 12 41 1,037 2007

1.18 Road lighting 70 503 163,306 2007

1.19 Improving tunnel safety 9 36 1,684 2009

1.20 Roadside rest and service areas 0 0 – 1997

1An additional 17 accident studies could not be summarised in the log odds metaanalysis.

2An additional 28 accident studies could not be summarised in the log odds metaanalysis.

equipment on the number of traffic accidents and injuries. The statistical weights are based on the size of the accident sample used in the evaluation studies. The largest numbers of studies are available for road lighting and cross-section improvements. For roadside rest and service areas, no studies have been found that quantify the effect on the number of accidents.

The size of the sample (number of sites and accidents) in studies on the effects of road layout and road equipment on accidents shows significant variations. Small samples, i.e. few sites and few accidents, pose a problem in many studies. This is particularly true regarding studies of the redesign of junctions, measures against accidents involving wild animals and horizontal curve treatments. Thus the statistical uncertainty in the results is particularly large in these measures.

The quality of research evaluating the effects of road layout and road equipment can be judged according to a number of criteria. The majority of studies on the effects of road layout and road equipment on accidents tend not to be based on a random sample of sites drawn from a known population or sampling frame. Strictly speaking, this means that the results of many studies cannot be generalised to places and conditions other than precisely those for which they were carried out. Only when a result is reproduced a number of times can it be assumed to have general validity. For road lighting and guardrails, the studies have, to a large extent, reached the same conclusion, although different study designs have been used. For black spot treatments, the opposite case holds. Here, the results diverge significantly, depending on the extent to which confounding factors were controlled for. The same is true to some extent of cycle tracks and lanes and channelisation of junctions.

Random and systematic measurement errors cannot be excluded in some studies.

Incomplete accident reporting is a general problem. Only a handful of studies have used more than one source of data for accidents, for example, accidents reported to the police and accidents registered at hospitals in order to test whether accident reporting affects the results.

In order to claim that a particular measure is a cause of changes in the accident figures, one must rule out that these changes are due to other events or factors, or to regression to the mean. Strictly speaking, such a requirement can only be fulfilled in experiments.

Only some of the measures against game accidents have been studied experimentally.

For all other measures affecting road layout and road equipment, the results presented come from more or less well-controlled non-experimental studies.

Many studies have not studied accidents on sites before and after a measure was implemented. Instead they compare accidents on road sections or at junctions with

different properties. The results of such studies do not necessarily say anything about how accident numbers can be expected to change after the implementation of a measure. This concerns mainly evaluations of channelisation of junctions, grade-separated junctions, cross-section improvements, and improving alignment and sight conditions. Differences in accident numbers may be due to other factors, e.g. a very narrow road may have more sharp curves than a wider road.

For some of the measures described in this chapter, studies are available that have estimated the effects of measures with regression models. That means these studies compare accident rates at sites with and without measure, or with different amounts of a measure, while at the same time controlling for a number of other factors. These studies are for the most part better in terms of control for confounding factors than ordinary case–control or before–after studies. The results could, however, not be included in the regular log odds meta-analysis and are therefore summarised only qualitatively.

For some measures, including cross-section improvement, improving alignment and sight distances and road lighting, there is a clear so-called dose–response relationship.

This means that the greater the dose of the measure that is implemented, the greater the change in the number of accidents. For example, a major improvement in road lighting reduces the number of accidents in darkness more than a minor improvement.

Some of the results are probably surprising for most people. It is important to find explanations for such surprising results. Nonetheless, in the majority of cases, it is difficult to point to any clear explanation of the results. Tracks for walking and cycling can serve as an example. No statistically significant changes in the number of accidents can be attributed to this measure. This may be due partly to the fact that more walking and cycling is induced by the tracks, partly that not all pedestrians or cyclists use the tracks for walking and cycling and partly that motor vehicles increase their speed.

Evidence of these and other possible changes in road user behaviour is, to a large extent, missing. As a result, these explanations, although reasonable, are no more than hypotheses of possible, but unsubstantiated explanations.

Main points of the effects of the measures on accidents

Measures that have been found to reduce the number of accidents include motorways, bypasses, grade-separated junctions, channelisation of junctions, roundabouts, road-side safety treatments, guardrails and crash cushions, some of the game accident measures and road lighting. Guardrails and crash cushions are effective in injury control, reducing the number of injury accidents but not always the number of

property-damage-only accidents. Many cross-section improvements and improvements of the alignment of roads reduce accidents as well.

For a number of measures, the effect varies substantially, depending on the design of the measure and site conditions. Certain forms of channelisation of junctions reduce the number of accidents but not all forms of channelisation do this. Roundabouts reduce the number of injury accidents, but appear to lead to more property damage only accidents. Improving the cross-section and alignment of roads may reduce the number of accidents, the effects are however complex and dependent, among other things, on the road standard, the consistency of geometric properties and on the effects on speed. It is therefore for the most part difficult to establish simple relationships between isolated geometric properties of roads and accidents. Combinations of geometric properties are mostly more important for accidents. Some game accident measures have also been found to reduce accidents when biological and ecological factors are taken into account in the design of the measures.

Certain road construction measures, including the construction of tracks for walking and cycling and new arterial roads in towns and cities do not appear to reduce the number of injury accidents. A possible explanation for this may be that the measures result in more traffic. These measures reduce the accident rate, but in certain cases, the reduction is totally or partially offset by an increase in the number of vehicle kilometres.

In some cases, there are indications that measures that have reduced the number of accidents at places where they have been implemented have led to an increased number of accidents elsewhere. This type of accident displacement from treated spots to other nearby locations is called accident migration. Tendencies towards accident migration have been found for game accident measures that lead to a reduction of game crossing at some road sections but to increased game crossings at other road sections (e.g. at the ends of fenced road sections). Tendencies towards accident migration have also been found for black spot treatment. Explanations are not very well known. In addition, there are so few studies that have found this type of tendency that it cannot be ascertained how widespread accident migration is in general.

Main points of the effects of the measures on mobility

Mobility is here taken to mean the quality of traffic flow in terms of the average speed over a given stretch of road, as well as the capacity of roads. Inducing new traffic can also be regarded as an increase of mobility. Table 1.0.2 shows the main points in current knowledge of the effect of the measures on mobility. New roads can lead to

induced traffic. For cycle lanes and tracks and tracks for walking and cycling, this means more walking and cycling, and for other new roads, more car traffic. However, the effects can vary substantially and are often modest, for example, for bypasses around smaller towns. Many measures have probably little or no effect on traffic volume. For a number of measures, the effect is unknown.

Most measures lead to increased speed, while only one measure leads to a reduction in speed, namely roundabouts. Nevertheless, the total passing time at a roundabout is, in many cases, less than, for example, at a signalised junction, since the waiting time is shorter and fewer vehicles have to come to a complete halt. Some game accident measures aim at reducing speed. Not all measures are however successful in reducing speed.

For some measures, the effect on the speed level is unknown. A number of such measures must, in many cases, be assumed to increase speed. Examples of these are cycle tracks and lanes and roadside safety treatments.

Table 1.0.2: Effects of road design and road equipment on mobility

Measure

Aspect of mobility Amount of traffic Speed level

1.1 Cycle lanes and tracks Increase Unknown

1.2 Motorways Increase Increase

1.3 Bypasses Increase Increase

1.4 Urban arterial roads Increase Increase

1.5 Channelisation of junctions None Increase

1.6 Roundabouts None Increase

1.7 Redesigning junctions None Unknown

1.8 Staggered junctions Unknown Unknown

1.9 Grade-separated junctions Unknown Increase

1.10 Black spot treatment Unknown Unknown

1.11 Cross-section improvements Unknown/increase Increase

1.12 Roadside safety treatment Unknown Unknown

1.13 Improving road alignment and sight distance Unknown Increase 1.14 Reconstruction and rehabilitation of roads Unknown Increase

1.15 Guard rails and crash cushions None None

1.16 Game accident measures None None/decrease

1.17 Horizontal curve treatments None Increase

1.18 Road lighting None Increase

1.19 Improving tunnel safety None Unknown

1.20 Roadside rest and service areas Unknown Unknown

Taken together, it can be concluded that the majority of measures in this area either increase or have a neutral effect on mobility. This is not surprising, since the main aim of extending and improving the road system is to increase mobility and reduce transport costs.

Main points on the effects of the measures on environmental conditions

Information about the effect of the measures on environmental conditions is relatively poor. For the majority of measures, either no studies are available or the available studies deal only with a few environmental aspects. Nonetheless, it is possible to indicate the likely effects of a number of measures based on general knowledge about the relationships between the amount of traffic and speed levels on the one hand and, for example, noise, exhaust emission and the spread of dust and dirt on the other hand.

Table 1.0.3summarises the main points in current knowledge about the effects of the Table 1.0.3: Main elements of the information available about effects on environmental conditions of road design and road equipment

Measure

Changes in noise levels and pollution

1.1 Cycle lanes and tracks Unknown

1.2 Motorways Unknown

1.3 Bypasses Decrease

1.4 Urban arterial roads Decrease

1.5 Channelisation of junctions Unknown

1.6 Roundabouts Decrease

1.7 Redesigning junctions Unknown

1.8 Staggered junctions Unknown

1.9 Grade-separated junctions Decrease

1.10 Black spot treatment Unknown

1.11 Cross-section improvements Unknown

1.12 Roadside safety treatment Unknown

1.13 Improving road alignment and sight distance Unknown 1.14 Reconstruction and rehabilitation of roads Unknown 1.15 Guard rails and crash cushions None

1.16 Game accident measures None

1.17 Horizontal curve treatments None

1.18 Road lighting Increase

1.19 Improving tunnel safety Unknown

1.20 Roadside rest and service areas Unknown

measures on environmental conditions. The table refers to local environmental conditions, rather than regional or global conditions.Table 1.0.3shows that the effects on noise and pollution are unknown for the majority of measures. Constructing new roads can reduce noise and pollution near the old road, since the old road is relieved of traffic. New roads are normally built further away from dwellings than existing roads.

All measures that affect mobility also are likely to affect noise and pollution. Increased traffic volumes will, all else being equal, increase noise and pollution. Increased speed may increase noise and pollution. However, when speed variations are reduced, noise and pollution may decrease. An example are roundabouts where fewer vehicles have to stop, or curve improvements that reduce the amount of braking and accelerating between curves or between curves and straight sections.

Some of the game accident measures have environmental impacts other than noise and pollution. Measures that aim at preventing game from crossing roads impair seasonal movements of game. Other measures affect both forestry and wood ecology.

Main elements in the costs of the measures

Table 1.0.4summarises the main points in the unit costs of the measures. Unit costs refer to the costs per kilometre of road where a measure is implemented, per junction or per curve. The cost figures inTable 1.0.4are average costs. The costs at individual sites can deviate significantly from the average. The unit costs of the measures vary considerably.Table 1.0.4shows only the investment costs for the measures described.

Some measures also entail operating and maintenance costs, for example guard rails and road lighting.

It is emphasised that the cost figures are uncertain for a number of measures. This is particularly true with regard to grade-separated junctions, roadside safety treatment and building roads through tunnels. No cost estimates are available for cross-section improvements and improvements of road alignment and sight conditions. These types of improvements can be achieved by numerous different measures and the depend, among other things, on the specific measure, the road type and standard and traffic volume.

Main points in the cost–benefit analyses

Cost–benefit analyses of the measures have been carried out to varying degrees. Where cost–benefit analyses are lacking, numerical examples have been worked out to indicate

the typical benefit–cost ratio if available data are good enough.Table 1.0.5sums up the results of the cost–benefit evaluations of the measures. The benefit–cost ratios vary substantially between the measures.

Measures that have been found to be cost-effective are bypasses, urban arterial roads, channelisation of junctions, roundabouts, grade-separated junctions, guardrails, curve improvements (background and directional marking), road lighting and building new Table 1.0.4: Main elements in the cost figures for road design and road equipment

Measure Unit

Average cost (million NOK)

Costs from year

1.1 Cycle lanes and tracks Kilometre road 3–7.8 2005^1,2

1.2 Motorway – class A Kilometre road 75.0 1995

1.2 Motorways – class B Kilometre road 22.5 1995

1.3 Bypasses Kilometre road 20.0 1995

1.4 Arterial roads in and around cities Kilometre road 60.0 1995 1.5 Channelisation of junctions – left turn lane main road Junction 0.5–0.8 2005² 1.5 Channelisation of junctions-side road channelisation Junction 0.2–0.4 2005² 1.5 Channelisation of junction-full channelisation Junction 1.2–1.8 2005²

1.6 Roundabouts (T-junction) Junction 2–4.8 2005^1,2

1.6 Roundabouts (X-junction) Junction 4.0–6.0 2005^1,2

1.7 Redesigning junction geometrics Junction 6.0 1995

1.8 Staggered junctions Junction 6.0 1995

1.9 Grade-separated junctions Junction 40.0 1995

1.10 Black spot treatment (average) Location 0.2 2009

1.11 Cross-section improvements Kilometre road – –

1.12 Roadside safety treatment Kilometre road 0.36 2005¹

1.13 Improving road alignment and sight conditions Kilometre road – – 1.14 General rehabilitation and reconstruction of road Kilometre road 4.0 1995 1.15 New safety guard rails (AADT 1,500–50,000) Kilometre road 0.6–0.8 2005¹ 1.16 Game accident measures – at-grade crossing Location 0.1 2008 1.16 Game accident measures – wood clearance (first-time) Kilometre road 0.04 1995 1.16 Game accident measures – wood clearance (annually) Kilometre road 0.004 1995

1.17 Marking signs in horizontal curves Curve 0.035 2005²

1.18 New road lighting (AADT 3,000–50,000) Kilometre road 0.4–1.3 2005^1,2

1.18 Improving road lighting Kilometre road 0.3 2007

1.19 Building road tunnels (four lanes, two tubes) Kilometre road 130–190 1995

1.20 Roadside rest and service areas Location 0.5 1995

1Erke and Elvik (2006).

2Statens vegvesen, Handbook 015 (2005; utkast 11 aug.).

arterial roads in tunnels. The cost–benefit ratios of these measures are for the most part dependent on the traffic volumes and number and severity of accidents. The cost for the measures also vary and are different, e.g. between different road types and terrains.

Cost–benefit ratios are therefore not always directly comparable between two Table 1.0.5: Cost–benefit evaluations of measures affecting road layout and road equipment

Measure Benefit–cost ratio

1.1 Cycle lanes 10

1.2 New motorway – class A (sparsely populated area) 0.15 1.2 New motorway – class B (sparsely populated area) 0.35

1.3 Bypasses (densely populated areas) 1.1

1.4 New urban arterial road 1.3

1.4 Expansion of main road in city from two to four lanes 2.3

1.5 Left turn lane at crossroads 3.4

1.5 Full channelisation of crossroads 3.4

1.5 Left turn lane at T-junction 1.6

1.6 Roundabouts at crossroads 2.2

1.6 Roundabouts at T-junctions 1.8

1.7 Redesigning junction geometric –

1.8 Staggered junctions 0.2–2.1

1.9 Grade-separated junctions 2.2

1.10 Black spot treatment 1.1–5.7

1.11 Cross section improvement –

1.13 Improvements of the alignment and sight distance – 1.14 General rehabilitation and reconstruction of roads 0.5

1.15 New guard rails 2.00

1.15 Repairing old guard rails 2.00

1.16 Game accident measures W1.00

1.16 Game accident measures – woodlance clearance annually 5.60 1.17 Background and directional markings on curves W1.00

1.18 New road lighting on motorways 0.21

1.18 New road lighting on rural roads (AADTo12,500) 0.27–0.95 1.18 New road lighting on rural roads (AADT W12,500) 1.36–4.01

1.18 New road lighting in towns o1

1.19 Urban arterial road in tunnel 1.10

1.19 Rural road in tunnel 0.20

1.20 Roadside rest and service areas –

alternative measures. For example, a roundabout requires more space than channelisa-tion of a juncchannelisa-tion, but is usually associated with larger benefits to a juncchannelisa-tion’s capacity and may have more favourable effects on severe accidents.

alternative measures. For example, a roundabout requires more space than channelisa-tion of a juncchannelisa-tion, but is usually associated with larger benefits to a juncchannelisa-tion’s capacity and may have more favourable effects on severe accidents.

In document Sistema de Despacho No Comercial. (página 96-112)