Alcohol and driving-How bad is the combination? A meta-analysis.

OBJECTIVE: The objective of this study was to summarize existing knowledge on the association between driving under the influence of alcohol and road safety outcomes and to assess factors that may explain why these estimates vary. METHODS: Based on studies of the association between blood alcohol concentration (BAC) levels and crashes, we used multilevel metaregression to calculate summary effects of BAC level and analyze potential moderators of the association. RESULTS: Based on 60 studies and 393 effect estimates, we found that BAC level, outcome severity, use of hospital data, and geographical region contributed to heterogeneity in results. CONCLUSION: The effect of BAC on crash and injury risk and culpability is stronger at higher BAC levels and for more serious outcomes. The relationship between BAC level and outcome is approximately exponential. The relationship is stronger in studies from Nordic countries than in studies from other countries, possibly because of the relatively low level of drunk driving in these countries. Studies based on hospital data and studies using non-crash-involved control groups find smaller effects on average.

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.

The illusion of absence: how a common feature of magic shows can explain a class of road accidents.

The purpose of the present note is to draw attention to the potential role of a recently discovered visual illusion in creating traffic accidents. The illusion consists in a compelling and immediate experience that the space behind an occluding object in the foreground is empty. Although the illusion refers to a region of space, which is invisible due to occlusion (a blind spot), there is evidence to suggest that it is nevertheless driven by visual mechanisms and that it can be just as deceptive and powerful as ordinary visual illusions. We suggest that this novel illusion can make situations involving blind spots in a road user's field of view even more dangerous than one would expect based on the lack of visibility by itself. This could be because it erroneously makes the road user feel that (s)he has actually seen everything there is to see, and thus has verified that the blind spot is empty. This hypothesis requires further testing before definitive conclusions can be drawn, but we wish to make researchers and authorities involved in the analysis of traffic accidents and on-the-spot crash investigations aware of its potential role in order to encourage registration of relevant data and facilitate further research.

Are helmeted cyclists taking more risk at signalized intersections?

OBJECTIVE: The aim of the present study was to investigate the relationship between bicycle helmet use and safety behavior at signalized intersections. Two hypotheses were investigated: The first states that bicycle helmet use leads to risker behavior because of the increased sense of protection (risk compensation), the other states that helmeted cyclists have a general inclination toward safer behavior (safety package) and that helmet use is one of several behaviors for improving safety. METHOD: Based on video recordings of 1031 cyclists at 12 signalized intersections in Denmark, two indicators of risky behavior were compared between helmeted and unhelmeted cyclists: Speed and time after the onset of yellow at which the cyclists crossed the stop line. Linear regression models were developed with gender, type of bicycle, and intersection characteristics as predictor variables, in addition to helmet use. RESULTS: Helmeted and unhelmeted cyclists do not differ in how many seconds after the onset of yellow they cross the stopping line. This is consistent with the absence of both risk compensation and safety package, alternatively with a general inclination of helmeted cyclists toward safer behavior which is about offset by risk compensation. Helmeted cyclists had higher speed on average, which indicates that risk compensation may occur. However, the higher speed may also be due to the generally better fitness of helmeted cyclists which is likely to result from larger cycling volumes. Moreover, the effect of helmet use on speed may be overestimated because of a lack of control for potential confounding variables. The results show further that, regardless of helmet use, before-red (lights on a separate bicycle signal shift to red before the main signal) is related to later crossings of the stop lane after the onset of yellow and that cyclists stop earlier on average at intersections with right-turn signals. CONCLUSIONS: The results do not provide support for the position that promoting or mandating bicycle helmet use will have adverse safety effects because of more risky behavior among helmeted cyclists.

Traffic volume and crashes and how crash and road characteristics affect their relationship - A meta-analysis.

The present study has investigated the relationship between traffic volume and crash numbers by means of meta-analysis, based on 521 crash prediction models from 118 studies. The weighted pooled volume coefficient for all crashes and all levels of crash severity (excluding fatal crashes) is 0.875. The most important moderator variable is crash type. Pooled volume coefficients are systematically greater for multi vehicle crashes (1.210) than for single vehicle crashes (0.552). Regarding crash severity, the results indicate that volume coefficients are smaller for more fatal crashes (0.777 for all fatal crashes) than for injury crashes but no systematic differences were found between volume coefficients for injury and property-damage-only crashes. At higher levels of volume and on divided roads, volume coefficients tend to be greater than at lower levels of volume and on undivided roads. This is consistent with the finding that freeways on average have greater volume coefficients than other types of road and that two-lane roads are the road type with the smallest average volume coefficients. The results indicate that results from crash prediction models are likely to be more precise when crashes are disaggregated by crash type, crash severity, and road type. Disaggregating models by volume level and distinguishing between divided and undivided roads may also improve the precision of the results. The results indicate further that crash prediction models may be misleading if they are used to predict crash numbers on roads that differ from those that were used for model development with respect to composition of crash types, share of fatal or serious injury crashes, road types, and volume levels.

Speeding and impaired driving in fatal crashes-Results from in-depth investigations.

OBJECTIVE: The aim of the study was to identify typical patterns of risk factors among speeding and impaired drivers involved in fatal crashes and to suggest countermeasures. METHOD: Results from in-depth investigations of 1,501 fatal passenger car crashes that occurred in Norway from 2005 to 2015 and involved 1,949 passenger cars are summarized. Relationships between speeding (excessive speed, EXC, or inappropriate speed, INAP); driving under the influence (DUI) of alcohol (ALC), drugs (DRUG), or both (MIX); and other driver-, crash-, vehicle-, and road-related variables were investigated. RESULTS: Speeding and DUI drivers have in common that they are more often male, unbelted, unlicensed, driving old cars, and involved in single-vehicle crashes under low-volume conditions (nighttime, weekend, low-volume roads). They are also less often fatigued, ill, or suicidal. EXC and ALC drivers are on average younger and they generally show more high-risk behavior than INAP, DRUG, and MIX drivers. In crashes with pedestrians/cyclists and crashes on slippery roads or in winter, INAP drivers are overrepresented and EXC and DUI drivers are underrepresented. Among DRUG and MIX drivers there may be differences according to the type of substance. CONCLUSIONS: Those drivers who show most types of high-risk behaviors, especially EXC and ALC drivers, are less likely to respond to measures relying on voluntary behavior changes, such as recommended speed, speed warnings, or classical enforcement, although such measures may be effective for INAP and some DRUG drivers. To change the behavior of EXC and ALC drivers, more restrictive measures are called for, such as non-overridable intelligent speed adaptation, vehicle impoundment, or Alcolock.

Inattention and distraction in fatal road crashes - Results from in-depth crash investigations in Norway.

Distraction and inattention pose a considerable threat to road safety, not only for car drivers, but also for vulnerable road users. Previous studies show that inattention and distraction are more often contributing factors in severe crashes, compared to less severe crashes. The correlation with severity appears to vary with the type of inattention. The aim of the present study was to conduct a comprehensive mapping of the types of inattention that contribute to fatal road crashes. This was done by exploring data from in-depth investigations of all fatal road crashes in Norway between 2011 and 2015 conducted by crash investigation teams of the Norwegian Public Roads Administration. Crash reports were selected for screening, based on codes indicating inattention as a possible contributing factor. Inattention among at-fault drivers of motor vehicles was found to contribute to almost one out of three fatal road crashes between 2011 and 2015. About one-third of inattention-related crashes involved pedestrians who were hit by motor vehicles, where the driver typically detected the pedestrian too late. Failure to check for information in blind spots or behind other sight obstructions is a typical form of inattention. Distraction by use of mobile phones contributed to between two and four percent of all fatal crashes, while other sources of distraction, within or outside of the vehicle, contributed to about ten percent. Driver inattention may be preventable by a system-oriented approach including a combination of vehicle technology, road and road environment improvements, appropriate signs and markings, education and information, as well as legal measures and enforcement regarding use of mobile phones, in-vehicle sight obstructions, and involvement in other secondary tasks during driving.

Vehicle registration year, age, and weight - Untangling the effects on crash risk.

The aim of the present study was to investigate the effects of passenger cars' first year of registration, weight, and age on the number of killed or seriously injured (KSI) car drivers, pedestrians, and cyclists. Poisson regression models were developed of injury crashes involving passenger cars in Norway in 2000-2016, with the following predictor variables: The cars' first year of registration and weight, either crash year or car age, the drivers age and gender, and in models for car-car collisions the crash partner cars' weight and either registration year or age. The results show that there are fewer KSI car drivers in more recent, newer, and heavier cars. It is estimated that the number of KSI car drivers in all types of crashes on average decreases by 6.7% for each consecutive registration year (-7.2% in car-car collisions and -6.0% in single vehicle crashes), increases by 3.7% for each consecutive year of age (+2.1% in car-car collisions and +5.3% in single vehicle crashes), and decreases by 4.9% on average for each 100 kg weight increase (-11.1% in car-car collisions and -2.3% in single vehicle crashes). In car-car collisions there are fewer KSI car drivers when the crash partner car is more recent (-4.4% for each consecutive registration year), and more KSI car drivers when the crash partner car is older (+4.1% for each consecutive year of age), or heavier (+6.8% per 100 kg weight increase). In collisions with pedestrians or cyclists, there are fewer KSI pedestrians/cyclists when the car is more recent (-3.3% per consecutive registration year) and more KSI pedestrians/cyclists when the car is heavier (+4.6% per 100 kg weight increase). Due to the large effects of safety improvements in more recent cars, an increased renewal rate in the passenger car fleet can be expected to contribute to large safety improvements. The increasing weight of more recent cars may contribute to improved safety for those who drive heavier cars, but overall the effect of increasing weight is probably small or even negative because heavier vehicles impose greater risk on other car drivers, pedestrians, and cyclists.

Recommend or mandate? A systematic review and meta-analysis of the effects of mandatory bicycle helmet legislation.

If all cyclistswere wearing helmets, significant numbers of head injuries might theoretically be prevented. Mandatory bicycle helmet legislation increases helmet use but is a controversial measure. Results from 21 studies of the effects of mandatory bicycle helmet legislation on injuries among crash involved cyclists were investigated by means of meta-analysis and the effects of several potential biases were investigated. The summary effect of mandatory bicycle helmet legislation for all cyclists on head injuries is a statistically significant reduction by 20% (95% confidence interval [-27; -13]). Larger effects were found for serious head injury (-55%; 95% confidence interval; [-78; -8]). Among children, larger effects were found when legislation applies to all cyclists than when it applies to children only. There is no clear indication of the results being affected by publication bias. Publication bias may exist, but any existing biases seem to more or less outweigh each other. Results from meta-analysis do not indicate that the results are systematically affected by a lack of control for time trend bias, choice of comparison group or study design (before-after vs. case control). Summary effects may be somewhat overestimated because of a lack of control for potential confounding variables in some of the studies. However, such a bias, if it exists, is not likely to be large. Empirical evidence for the hypotheses that mandatory bicycle helmet legislation deters people from cycling and that helmet wearing leads to behavioral adaptation is mixed. In summary, mandatory bicycle helmet legislation can be expected to reduce head injury among crash involved cyclists. Some adverse effects may occur, but will not necessarily be large or long-lasting. People who may be deterred from cycling, are among those with the highest injury risk and the smallest health effects from cycling. If the overall goal is to improve safety for all cyclists and to increase cycling, mandatory bicycle helmet legislation should be supplemented by other measures, especially improved bicycle infrastructure.

Bicycle helmets - To wear or not to wear? A meta-analyses of the effects of bicycle helmets on injuries.

A meta-analysis has been conducted of the effects of bicycle helmets on serious head injury and other injuries among crash involved cyclists. 179 effect estimates from 55 studies from 1989-2017 are included in the meta-analysis. The use of bicycle helmets was found to reduce head injury by 48%, serious head injury by 60%, traumatic brain injury by 53%, face injury by 23%, and the total number of killed or seriously injured cyclists by 34%. Bicycle helmets were not found to have any statistically significant effect on cervical spine injury. There is no indication that the results from bicycle helmet studies are affected by a lack of control for confounding variables, time trend bias or publication bias. The results do not indicate that bicycle helmet effects are different between adult cyclists and children. Bicycle helmet effects may be somewhat larger when bicycle helmet wearing is mandatory than otherwise; however, helmet wearing rates were not found to be related to bicycle helmet effectiveness. It is also likely that bicycle helmets have larger effects among drunk cyclists than among sober cyclists, and larger effects in single bicycle crashes than in collisions with motor vehicles. In summary, the results suggest that wearing a helmet while cycling is highly recommendable, especially in situations with an increased risk of single bicycle crashes, such as on slippery or icy roads.

How would increasing seat belt use affect the number of killed or seriously injured light vehicle occupants?

The expected effects of increasing seat belt use on the number of killed or seriously injured (KSI) light vehicle occupants have been estimated for three scenarios of increased seat belt use in Norway, taking into account current seat belt use, the effects of seat belts and differences in crash risk between belted and unbelted drivers. The effects of seat belts on fatality and injury risk were investigated in a meta-analysis that is based on 24 studies from 2000 or later. The results indicate that seat belts reduce both fatal and non-fatal injuries by 60% among front seat occupants and by 44% among rear seat occupants. Both results are statistically significant. Seat belt use among rear seat occupants was additionally found to about halve fatality risk among belted front seat occupants in a meta-analysis that is based on six studies. Based on an analysis of seat belt wearing rates among crash involved and non-crash involved drivers in Norway it is estimated that unbelted drivers have 8.3 times the fatal crash risk and 5.2 times the serious injury crash risk of belted drivers. The large differences in crash risk are likely to be due to other risk factors that are common among unbelted drivers such as drunk driving and speeding. Without taking into account differences in crash risk between belted and unbelted drivers, the estimated effects of increasing seat belt use are likely to be biased. When differences in crash risk are taken into account, it is estimated that the annual numbers of KSI front seat occupants in light vehicles in Norway could be reduced by 11.3% if all vehicles had seat belt reminders (assumed seat belt wearing rate 98.9%), by 17.5% if all light vehicles had seat belt interlocks (assumed seat belt wearing rate 99.7%) and by 19.9% if all front seat occupants of light vehicles were belted. Currently 96.6% of all (non-crash involved) front seat occupants are belted. The effect on KSI per percentage increase of seat belt use increases with increasing initial levels of seat belt use. Had all rear seat occupants been belted, the number of KSI front seat occupants could additionally be reduced by about 0.6%. The reduction of the number of KSI rear seat occupants would be about the same in terms of numbers of prevented KSI.

Safety effects of fixed speed cameras - An empirical Bayes evaluation.

The safety effects of 223 fixed speed cameras that were installed between 2000 and 2010 in Norway were investigated in a before-after empirical Bayes study with control for regression to the mean (RTM). Effects of trend, volumes, and speed limit changes are controlled for as well. On road sections between 100m upstream and 1km downstream of the speed cameras a statistically significant reduction of the number of injury crashes by 22% was found. For killed and severely injured (KSI) and on longer road sections none of the results are statistically significant. However, speed cameras that were installed in 2004 or later were found to reduce injury crashes and the number of KSI on road sections from 100m upstream to both 1km and 3km downstream of the speed cameras. Larger effects were found for KSI than for injury crashes and the effects decrease with increasing distance from the speed cameras. At the camera sites (100m up- and down-stream) crash reductions are smaller and non-significant, but highly uncertain and possibly underestimated.

Safety effects of section control--an empirical Bayes evaluation.

The safety effects of section control were investigated at 14 sites in Norway. A before-after study was conducted with the empirical Bayes method in order to control for regression to the mean (RTM). Effects of trend, volumes, speed limit changes and speed cameras at some of the sites in the before period are controlled for as well. For injury crashes a non-significant reduction by 12% was found. The number of killed or severely injured was found to be significantly reduced by 49% at the section control sites. The results indicate that the crash reductions in tunnels (most of which are undersea tunnels with section control on steep downhill segments) are at least of the same magnitude as on open roads. The results are consistent with findings from speed measurements, although the crash reductions are larger than one would expect as a result from the speed reductions. Downstream of the section control sites (up to 3 km in each direction) injury crashes were found to be significantly reduced by 46%. The number of KSI downstream of the section control sites is too small for drawing any conclusions. It is concluded that section control is effective in reducing both speed and crashes, especially serious crashes, and that spillover effects (crash reductions at non-enforcement sites) are more likely to occur than crash migration. The size of the effects that were found should be interpreted with caution because of the relatively short after periods for some of the sites and the sensitivity of the results to the outcomes of individual crashes.

Speed cameras, section control, and kangaroo jumps-a meta-analysis.

A meta-analysis was conducted of the effects of speed cameras and section control (point-to-point speed cameras) on crashes. 63 effect estimates from 15 speed camera studies and five effect estimates from four section control studies were included in the analysis. Speed cameras were found to reduce total crash numbers by about 20%. The effect declines with increasing distance from the camera location. Fatal crashes were found to be reduced by 51%, this result may however be affected by regression to the mean (RTM). Section control was found to have a greater crash reducing effect than speed cameras (-30% for total crash numbers and -56% for KSI crashes). There is no indication that these results (except the one for the effect of speed cameras on fatal crashes) are affected by regression to the mean, publication bias or outlier bias. The results indicate that kangaroo driving (braking and accelerating) occurs, but no adverse effects on speed or crashes were found. Crash migration, i.e., an increase of crash numbers on other roads due to rerouting of traffic, may occur in some cases at speed cameras, but the results do not indicate that such effects are common. Both speed cameras and section control were found to achieve considerable speed reductions and the crash effects that were found in meta-analysis are of a similar size or greater than one might expect based on the effects on speed.

Still red light for red light cameras? An update.

The present study has replicated the results from a previous meta-analysis by Erke (2009) [Erke, A., 2009. Red light for red-light cameras? A meta-analysis of the effects of red-light cameras on crashes. Accident Analysis & Prevention 41 (5), 897-905.] based on a larger sample of RLC-studies, and provides answers to the criticisms that were raised by Lund et al. (2009) [Lund, A.K., Kyrychenko, S.Y., Retting, R.A., 2009. Caution: a comment on Alena Erke's red light for red-light cameras? A meta-analysis of the effects of red-light cameras on crashes. Accident Analysis and Prevention 41, 895-896.] against the previous meta-analysis. The addition of recent studies to the meta-analysis and a more thorough investigation of potential moderator variables lead to a slight improvement of the estimated effects of RLC in the previous meta-analysis. The present study found a non-significant increase of all crashes by 6% and a non-significant decrease of all injury crashes by 13%. Right-angle collisions were found to decrease by 13% and rear-end collisions were found to increase by 39%. For right-angle injury collisions a decrease by 33% was found and for rear-end injury collisions a smaller increase was found (+19%). The effects of RLC are likely to be more favorable when RLC-warning signs are set up at main entrances to areas with RLC enforcement than when each RLC-intersection is signposted. The effects of RLC may become more favorable over time, this could however not be investigated empirically. Several results indicate that spillover effects may occur for right-angle collisions, but most likely not for rear-end and other crashes. If spillover effects do not occur for rear-end crashes, which increase at RLC intersection, this would be a positive result for RLC. However, the results seem to be affected to some degree by publication bias and the effects may therefore be somewhat less favorable than indicated by the results from meta-analysis.

The effects of electronic stability control (ESC) on crashes--an update.

The present study is an update of the meta-analysis by Erke (Erke, A., 2008. Effects of Electronic Stability Control (ESC) on accidents: a review of empirical evidence. Accident Analysis & Prevention, 40 (1), 167-173). Results from 12 studies of the effects of Electronic Stability Control (ESC) on the number of different types of crashes were summarized by means of meta-analysis. The results indicate that ESC prevents about 40% of all crashes involving loss of control. The greatest reductions were found for rollover crashes (-50%), followed by run-off-road (-40%) and single vehicle crashes (-25%). These results are however likely to be somewhat overestimated, especially for non-fatal crashes. Multiple vehicle crashes were found to be largely unchanged. Reductions were found for some types of multiple vehicle crashes. Rear-end collisions are unchanged or may increase. Fatal crashes involving pedestrians, bicycles or animals were found to increase as well. ESC was found to be more effective in preventing fatal crashes than non-fatal crashes. ESC is often found to be more effective in Sports Utility Vehicles (SUVs) than in passenger cars. This may be due to differences between drivers of SUVs and passenger cars. The results from meta-analysis indicate that drivers of ESC-equipped vehicles are likely to be safer drivers than other drivers. All the same, ESC may lead to behavioural adaptation in some cases, but it is not likely that behavioural adaptation offsets the positive safety effects. This may be due to a lack of knowledge about ESC.

Are airbags a dangerous safety measure? A meta-analysis of the effects of frontal airbags on driver fatalities.

A meta-analysis has been conducted of the effectiveness of frontal airbags in reducing driver fatalities, and some potential moderator variables for airbag effectiveness have been investigated. The results confirm the assumption that airbags reduce accident fatalities among belted drivers, but the results are too heterogeneous for drawing conclusions about the size of the overall effect. No support has been found for the hypothesis that airbags increase overall fatality risk, as has been found in the study by Meyer and Finney (Meyer, M., Finney, T., 2005. Who wants Airbags? Chance, 18 (19) 3-16). The results do not seem to be affected by publication bias, and no indications of confounding effects of vehicle characteristics or impact velocity have been found. In frontal collisions belted driver fatalities were found to be reduced by about 22% when all types of airbags are regarded together. The revision of the test criteria for airbags in the USA in 1997 has improved airbag effectiveness. For unbelted drivers airbags are neither effective nor counterproductive, but may increase fatality risk in single vehicle accidents. The results show that there is a lack of knowledge about the effects of airbags in accidents that are not frontal collisions.