Safety effects of bypass lanes at unsignalized three-leg junctions.

Bypass lanes are a low-cost measure to increase capacity at unsignalized T-junctions without left-turn lanes that allow through-traffic to pass left-turning vehicles on the right. There is very limited knowledge about the safety effects of bypass lanes. We found six previous studies that could be summarized by means of meta-analysis, and the results show an average accident reduction of 10 percent. However, the results from previous studies are inconsistent and may be biased. Therefore, the present study has estimated safety effects of by-pass lanes in Norway, based on a sample of 2,227 T-junctions (incl. 94 with bypass-lanes) for which relevant data was available for a period of up to 10 years. We developed accident prediction models and conducted before-after analyses. The accident prediction models show that junctions with bypass lanes have 82 percent more accidents than junctions without bypass lanes, when controlling for endogeneity. Endogeneity occurs when the implementation of a measure is conditional on the frequency of crashes, as has been the case with bypass lanes. The before-after analysis shows that average accident numbers decrease after the installation of bypass lanes. However, when controlling for regression-to-the-mean (RTM), average accident numbers increase. RTM means that accident numbers would have been likely to decrease even without any measure because they had been exceptionally high in the before period. The control for potential biases in our study is likely to contribute to the discrepancy between results from our study and previous studies, most of which have not controlled for the same potential biases. We conclude therefore that bypass lanes, although favorable for capacity, are likely to be unfavorable for safety when compared to other unsignalized T-junctions without left-turn lanes. Unfavorable safety effects may partly be due to site specific conditions, such as road alignment and sight conditions, that contribute to rear-end collision risk or inappropriate driver behavior. However, this does not necessarily mean that bypass lanes never should be used. For example, at junctions where a bypass lane may solve capacity problems, and where site-specific conditions are favorable, bypass lanes may still be an acceptable solution.

The development of a road safety policy index and its application in evaluating the effects of road safety policy.

The paper presents an exploratory study of a road safety policy index developed for Norway. The index consists of ten road safety measures for which data on their use from 1980 to 2021 are available. The ten measures were combined into an index which had an initial value of 50 in 1980 and increased to a value of 185 in 2021. To assess the application of the index in evaluating the effects of road safety policy, negative binomial regression models and multivariate time series models were developed for traffic fatalities, fatalities and serious injuries, and all injuries. The coefficient for the policy index was negative, indicating the road safety policy has contributed to reducing the number of fatalities and injuries. The size of this contribution can be estimated by means of at least three estimators that do not always produce identical values. There is little doubt about the sign of the relationship: a stronger road safety policy (as indicated by index values) is associated with a larger decline in fatalities and injuries. A precise quantification is, however, not possible. Different estimators of effect, all of which can be regarded as plausible, yield different results.

Risk of road traffic injury in Norway 1970-2022.

This paper describes changes in the risk of road traffic injury in Norway during the period from 1970 to 2022. During this period, the risk of fatal and personal injury declined by more than 70 % for most groups of road users. There are five main potential explanations of a decline in the risk of injury: (1) a reduced probability of accidents that have the potential for causing injury; (2) an improved protection against injury given that an accident has occurred; (3) improved medical care increasing the survival rate, given an injury (this would reduce the number of fatalities, but not the number of injuries); (4) a tendency for the reporting of injuries in official accident statistics to decline over time; (5) uncertain or erroneous estimates of the exposure to the risk of injury. The decline in the risk of road traffic injuries in Norway after 1970 can probably be attributed to a combination of reduced reporting of injuries in official statistics, improved protection against injury in accidents, and (for fatal injuries) improved medical care. Insurance data, available from 1992, do not indicate a reduction in the risk of accidents leading to insurance claims. Incomplete and possibly erroneous data for mopeds and motorcycles make it impossible to identify sources of changes in injury risk over time for these modes of transport.

Risk factors as causes of accidents: Criterion of causality, logical structure of relationship to accidents and completeness of explanations.

The causes of accidents are studied in the belief that by finding causes, accidents can be prevented by removing or controlling their causes. It follows that the risk factors that have traditionally been regarded as contributing to accidents can only be regarded as causes if it is possible to alter them by means of one or more road safety measures. Risk factors are causes if their relationship to accidents can be changed by implementing one or more road safety measures influencing the risk factors. Hence, road safety measures that could have been implemented to change risk factors identified as contributing to an accident, but have not, are also causes of accidents. Many of the human factors that have traditionally been identified as risk factors for accidents, like age, gender, driving experience, expectations or involuntary inattention are not causes of accidents, because they cannot be changed by means of any realistic road safety measure. What cannot be changed (could not have been different) is not a cause. It is possible, both in case studies and in statistical analyses, to determine when a set of factors precipitating or contributing to accidents is complete. A list of road safety measures that could have been implemented is only limited by our creativity and imagination and will therefore never be complete.

A comparative analysis of accident modification functions for traffic law enforcement.

Traffic law enforcement is a road safety measure whose effects on accidents or injuries is best described by means of a function rather than a point estimate. An informative function should comprise both increases and decreases in enforcement. Currently available accident modification functions cannot serve this need. A fruitful approach to developing accident modification functions covering both increases and decreases in enforcement is differences-in-differences estimates based on multivariate accident prediction models. The paper explains how to develop such estimates and illustrates them. The interpretation of the results of empirical studies can be informed by a game-theoretic model of the effects of enforcement, previously published in Accident Analysis and Prevention (Bjørnskau and Elvik 1992, 507-520).

What would a road safety policy fully consistent with safe system principles mean for road safety?

If fully implemented, the Safe System principles as formulated by the International Transport Forum would lead to a considerably safer road transport system. The aims of this paper are: (1) To define operationally what full consistency with Safe System principles means; (2) To estimate the potential effects on traffic fatalities of full compliance with the Safe System principles. Operational definitions of full consistency with Safe System principles are proposed for speed limits, road design, road maintenance, vehicle safety and road user compliance with road traffic law. Estimates for Norway indicate that by complying perfectly with Safe System principles in all these areas, the number of fatalities could be reduced by 50-70 %. This is a conservative estimate. This shows that the Safe System principles are well justified scientifically: adhering to them would greatly improve road safety. However, currently road safety policy in many countries, including Norway, fails to realise these improvements in safety by not complying with the Safe System principles.

Does empirical evidence support the effectiveness of the Safe System approach to road safety management?

The objective of this paper is to evaluate the effectiveness of the Safe System approach to road safety management, as implemented in Norway. The paper proposes simple operational definitions of key elements of the Safe System approach to road safety management. The relationship between these elements and changes over time in the number of killed or seriously injured road users in Norway is studied by means of negative binomial regression models. These models do not support a causal interpretation of the findings, but predict systematic patterns in findings that, if replicated in other data sets, at least make a causal interpretation plausible, although not incontestable. The findings reported in this paper are broadly consistent with theoretical predictions and therefore support the effectiveness of the Safe System approach. It is highly likely that the adoption of the Safe System approach to road safety management in Norway has contributed to a larger improvement in road safety than would otherwise have occurred.

Effects on accidents of technical inspections of heavy goods vehicles in Norway: A re-analysis and a replication.

INTRODUCTION: This paper presents a re-analysis of a previous study of the effects on accidents of technical inspections of heavy vehicles in Norway and a replication of the study using more recent data. METHOD: Increasing the number of technical inspections is associated with a reduction in the number of accidents. Reducing the number of inspections is associated with an increase in the number of accidents. The relationship between changes in the number of inspections and changes in the number of accidents is well described by means of logarithmic dose-response curves. RESULTS: These curves show that inspections had a larger effect on accidents in the recent period (2008-2020) than in the first period (1985-1997). Based on recent data, a 20% increase in the number of inspections is associated with a 4-6% reduction in the number of accidents. A 20% reduction of the number of inspections is associated with a 5-8% increase in the number of accidents.

Changes over time in the relationship between road accidents and factors influencing them: The case of Norway.

This paper compares the results found in successive accident prediction models developed at the national level for Norway. Over time, the models have become more comprehensive in terms of the roads and the variables included in them. It is found that traffic volume has consistently had the strongest association with the number of accidents. It explains nearly all the systematic variation in the number of accidents. The second most important variable has consistently been the speed limit of 50 km/h, which indicates an urban area (the default speed limit in urban areas in Norway is 50 km/h). This variable has become less important over time. Motorways (freeways) have consistently had a lower accident rate than other roads. The mean number of accidents per road section declined considerably from 1986 to 89 to 2010-15. Systematic variation in the number of accidents between road sections was greatly reduced. At present, the variation in the annual number of accidents between road sections is mostly random.

Further compelling evidence for safety-in-numbers: It is more than meets the eye.

In the extant road safety literature, estimating safety-in-numbers is dominated by conventional cross-sectional methods in which active mode (pedestrian or cyclist) volume together with motorised traffic volume are present in regression models explaining active mode safety directly. There is "direct" evidence for safety-in-numbers when the coefficient associated with active mode volume is negative (safety improves as volume increases) or when it is smaller than one (safety decreases at a lower rate compared to the rate of increase in active mode volume). In this article we extend the concept of safety-in-numbers in the traffic safety field, introducing "indirect" safety-in-numbers, which constitutes a new form of evidence for this phenomenon. We provide empirical evidence to support this, discussing that using an approach based on heterogeneity in mean modelling-a form of random parameters (slopes) models-it is possible to reveal "indirect" safety-in-numbers effects. Therefore, such models can reveal further compelling evidence for safety-in-numbers. Accurate knowledge of safety-in-numbers effects (both direct and indirect) and their underlying mechanisms can help provide robust motives for promoting active travel and will have valuable implications for the design of road safety interventions.

Driver mileage and accident involvement: A synthesis of evidence.

The relationship between driver mileage and accident involvement has been a controversial topic for at least 20 years. The key issue is whether driver accident involvement rate increases in proportion to miles driven or has a non-linear relationship to miles driven. This paper presents a synthesis of evidence from studies of how the number of accidents per driver per unit of time relates to distance driven in the same period. Most studies of this relationship are methodologically weak and their results highly inconsistent and potentially misleading. Unreliable data and poor control for confounding factors characterise most studies. Only a few studies based on multivariate statistical models control for at least some of the confounding factors that may influence the relationship between distance driven and accident involvement. These studies consistently show that the number of accidents per driver per year increases less than in proportion to distance driven. A good approximation is that the number of accidents per driver per unit of time is proportional to the square root of distance driven. Potential methodological and substantive explanations of this finding are discussed.

Why are there so few experimental road safety evaluation studies: Could their findings explain it?

Randomised controlled trials (also known as experiments) are widely regarded as the best design of studies that aim to estimate the effects of a treatment, like a road safety measures. However, as noted by Hauer (2016) there are few randomised controlled trials in the field of road safety. Hauer has suggested (2019) that not finding an effect of the measure being evaluated could be one reason for this. This paper provides an inventory of experimental evaluations of road safety measures. 24 different road safety measures have been evaluated experimentally. More than one experiment was reported for 8 road safety measures; for the other 16 only a single experiment was found. With few exceptions, experiments find no effect on accidents of the measures subjected to experiments. Most of the exceptions are due either to failure of randomisation or refer to measures whose effects tend to erode as they become more commonly used. Thus, the effects found in initial experiments with daytime running lights and high-mounted stop lamps have gradually eroded as more cars got these systems. Driver training is one of the few road safety measures for which more than one experiment has been carried out. Results consistently show no effect on accidents of driver training.

How can regulatory authorities improve safety in organizations by influencing safety culture? A conceptual model of the relationships and a discussion of implications.

Regulators have increasingly started to focus on safety culture. The causal link between regulatory initiatives to improve safety culture and a potential decline in accidents may, however, appear like a "black box", involving social processes that seem hard to foresee and influence. We need a better conceptual understanding of this. The aims of our study are to: 1) Map studies of regulatory efforts to influence safety culture in companies, 2) Use the identified studies to develop a conceptual model of the analytical relationships between regulatory initiatives to improve safety culture and accidents in these studies, including the factors influencing these analytical relationships and 3) discuss practical implications. The review is reported according to PRISMA-guidelines, and focuses on professional transport (aviation, sea, rail, road) and the Norwegian petroleum sector. Our review indicates at least six analytical relationships, mediating between regulatory attempts to influence organizational safety culture and accidents. These are between: 1) Rules and regulators, 2) Regulators and companies, 3) Managers and employees in the companies, 4) Organizational members' shared ways of thinking and acting, which are the two key elements of safety culture, 5) Safety culture and safety behaviour, and between 6) Safety behaviour and accidents. Regulatory attempts to influence safety culture may fail or succeed at each level, through factors involved in the different relationships.

Democracy, governance, and road safety.

Countries scoring high on the Democracy Index developed by The Economist Intelligence Unit have fewer traffic fatalities per 100,000 inhabitants than countries scoring low on this index. The statistical relationship between democracy score and fatalities per 100,000 inhabitants is statistically highly significant and robust with respect to control for potentially confounding factors. A similar relationship exists between democracy score and the number of traffic fatalities per 100,000 motor vehicles. The statistical relationship between level of democracy and level of road safety is strong, although the analyses reported in this paper do not justify a causal interpretation of the relationship. Changes over time in government effectiveness (one of the indicators of the World Governance Index developed by the World Bank) are weakly associated with changes in road safety performance.

First steps towards a holistic impact assessment methodology for connected and automated vehicles.

Connected and automated vehicles have become more common in recent years, increasing the need to assess their societal level impacts. In this paper a methodology is presented to explore and define relevant impact areas as a starting point for quantitative impact assessment. The many interrelations between impact areas increases the complexity of obtaining a complete overview. Therefore, a structured approach is used, which shows many similarities with the modelling of causal-loop-diagrams. Feedback loops between impact areas are taken into account at an early stage and methods of literature research, project team feedback, interrelation assessment and grouping are used to produce a holistic overview of impacts. The methodology was developed and applied in the European H2020 project LEVITATE. The impact taxonomy and interrelations between impact areas resulting from this project are presented and further steps needed to perform a quantitative evaluation of the impacts are discussed.

Crash risk on entrance versus exit zones of road bridges in Norway.

Using data from the national register of police-reported crashes and from the bridge register of the Norwegian Public Roads Administration, we estimated rates of single-vehicle crashes on road sections adjacent to road bridges and on different sections of the bridges. Data included all single-vehicle personal injury crashes occurring on or close to road bridges in Norway between 2010 and 2016, a total of 219 crashes. All bridges on state and county roads were included. Crash rate was found to be highest in the approach zone of short bridges (last 50 m before bridge) and lowest in the middle of long bridges. On bridges shorter than about 100 m, crash rate was higher in the first than in the last bridge zone. Total crash rate on bridges was close to the figure for the total road network. However, for the approach to short bridges, crash rate was significantly higher than for the total road network, and for the middle part of long bridges it was significantly lower. A supplementary analysis of in-depth data from 31 fatal crashes including both single-vehicle and multiple-vehicle crashes supported the results from the main analysis. A higher proportion of fatal crashes occurred on approaching or entering a bridge than when leaving the bridge, as seen from the direction of travel of the at-fault vehicle. Concerning countermeasures against bridge accidents, particular attention should be payed to the approach zone and to the design of barriers.

Can the use of road safety measures on national roads in Norway be interpreted as an informal application of the ALARP principle?

The ALARP principle, stating that risks should be reduced to a level "As Low As Reasonably Practicable", is widely known and discussed in risk management. The principle is flexible, as the interpretation of the key concepts of reasonable and practicable can be adapted to different contexts. This paper discusses whether the use of road safety measures on national roads in Norway can be interpreted as an informal application of the ALARP-principle. According to official guidelines, priority setting for major road investments should be based on cost-benefit analysis. Most road safety measures are low-cost projects that have traditionally not been subject to cost-benefit analysis. A use of these measures regarded as reasonable in the ALARP sense may include considerations of cost, efficiency and fair distribution. Data on 328 road safety measures implemented around 2000 is used to evaluate factors influencing their use. It is argued that the use of these measures is consistent with an informal application of the ALARP-principle.

A Transport Policy Whose Injury Impacts May Go Unnoticed: More Walking, Cycling and Use of Public Transport.

It is an objective of transport policy in many countries and cities to promote walking, cycling and the use of public transport. This policy seeks to improve public health and reduce emissions contributing to global warming. It is, however, very likely that more walking, cycling and use of public transport will be associated with an increase in traffic injury. Moreover, it is likely that most of this increase will go unnoticed and not be recorded in official road accident statistics. Official statistics on traffic injury are known to be very incomplete as far as injuries to pedestrians, cyclists and public transport passengers are concerned. This incompleteness is a problem when assessing health impacts of more walking, cycling and travel by public transport. In this paper, studies made in the city of Oslo, Norway (population 700,000) are used to develop numerical examples showing how the estimated real and recorded number of injuries may change when 10% of person km of travel performed by car are transferred to walking, cycling or public transport. It is shown that not more than about 2% of the estimated change in the actual number of injured road users will be recorded by official statistics on traffic injury.

The more (sharp) curves, the lower the risk.

The risk of accident in horizontal curves is a complex function of at least the following characteristics of the curve: the radius of the curve; the length of the curve (and the resultant deflection angle); the presence of a spiral transition curve; the super-elevation of the curve; the distance to adjacent curves; and whether the curve is on a flat road, a straight gradient or a vertical curve. The interactions between these characteristics in determining accident risk in horizontal curves is only beginning to be understood. This paper summarises the results of studies that have investigated the interaction between the radius of a horizontal curve and the distance to adjacent curves. The shorter the mean distance between curves, the lower is the increase in risk for a given curve radius. The sharper neighbouring curves are, the lower is the increase in risk for a given curve radius. Thus, overall risk may not be higher on a road consisting mostly of sharp curves than on a road consisting mostly of straight sections with a few curves located far apart from each other.

A systematic cost-benefit analysis of 29 road safety measures.

Economic evaluations of road safety measures are only rarely published in the scholarly literature. We collected and (re-)analyzed evidence in order to conduct cost-benefit analyses (CBAs) for 29 road safety measures. The information on crash costs was based on data from a survey in European countries. We applied a systematic procedure including corrections for inflation and Purchasing Power Parity in order to express all the monetary information in the same units (EUR, 2015). Cost-benefit analyses were done for measures with favorable estimated effects on road safety and for which relevant information on costs could be found. Results were assessed in terms of benefit-to-cost ratios and net present value. In order to account for some uncertainties, we carried out sensitivity analyses based on varying assumptions for costs of measures and measure effectiveness. Moreover we defined some combinations used as best case and worst case scenarios. In the best estimate scenario, 25 measures turn out to be cost-effective. 4 measures (road lighting, automatic barriers installation, area wide traffic calming and mandatory eyesight tests) are not cost-effective according to this scenario. In total, 14 measures remain cost-effective throughout all scenarios, whereas 10 other measures switch from cost-effective in the best case scenario to not cost-effective in the worst case scenario. For three measures insufficient information is available to calculate all scenarios. Two measures (automatic barriers installation and area wide traffic calming) even in the best case do not become cost-effective. Inherent uncertainties tend to be present in the underlying data on costs of measures, effects and target groups. Results of CBAs are not necessarily generally valid or directly transferable to other settings.