Possibilities to reduce pavement rehabilitation cost of a collision-free road investment using an LCCA design procedure

In the past decades, many single carriageway roads in Sweden have been converted to collision-free roads as a cost-effective alternative to conventional motorways. Investigations have concluded that the road type has been successful in reducing the number of fatal accidents, despite increased operation and maintenance costs. In recent years, the focus has shifted to converting narrower roads, which are anticipated to further increase pavement rehabilitation cost but also complicate traffic management during road works. This paper first examines the consequences in terms of road agency and road user costs; second, the possibilities to influence future costs by design alternatives. A life cycle cost analysis was employed to study future costs. The analysis indicated significant increase in life cycle cost compared to a single carriageway road. The analysis of design alternatives also indicated that future agency and road user cost can be substantially improved by finding an optimal alternative.     

Quasi-induced exposure: The choice of exposure metrics

The quasi-induced exposure method is widely used to estimate exposure and risks of different groups of drivers and vehicles. Essentially, this method assumes that non-at-fault or passive parties in two-vehicle collisions represent a random sample of the populations on the road. Most previous works have used the whole sample of collisions to estimate exposure.There has been some concern about possible biases in quasi-induced estimates. In this paper, we argue that (1) biases are mainly due to differences in accident avoidance abilities, speeds and injury risks, and (2) because the influence of these three factors on the probability of being non-at-fault is not the same for every crash type, differences may arise among non-at-fault populations, in which case some crash types would provide a more accurate estimate of exposure than others.We explore the direction of biases due to speed, accident avoidance ability and injury risk in four accident types: accidents between vehicles travelling on different lanes in two-way, two-lane undivided roads; accidents between vehicles travelling on different lanes on multilane roads; intersection accidents; and accidents between vehicles travelling on the same lane. Our analysis shows that more research would be needed concerning the effect of speed on head-on crashes on undivided roads, and crashes on multilane roads.     

A crash-prediction model for multilane roads

Considerable research has been carried out in recent years to establish relationships between crashes and traffic flow, geometric infrastructure characteristics and environmental factors for two-lane rural roads. Crash-prediction models focused on multilane rural roads, however, have rarely been investigated. In addition, most research has paid but little attention to the safety effects of variables such as stopping sight distance and pavement surface characteristics. Moreover, the statistical approaches have generally included Poisson and Negative Binomial regression models, whilst Negative Multinomial regression model has been used to a lesser extent. Finally, as far as the authors are aware, prediction models involving all the above-mentioned factors have still not been developed in Italy for multilane roads, such as motorways. Thus, in this paper crash-prediction models for a four-lane median-divided Italian motorway were set up on the basis of accident data observed during a 5-year monitoring period extending between 1999 and 2003. The Poisson, Negative Binomial and Negative Multinomial regression models, applied separately to tangents and curves, were used to model the frequency of accident occurrence. Model parameters were estimated by the Maximum Likelihood Method, and the Generalized Likelihood Ratio Test was applied to detect the significant variables to be included in the model equation. Goodness-of-fit was measured by means of both the explained fraction of total variation and the explained fraction of systematic variation. The Cumulative Residuals Method was also used to test the adequacy of a regression model throughout the range of each variable. The candidate set of explanatory variables was: length (L), curvature (1/R), annual average daily traffic (AADT), sight distance (SD), side friction coefficient (SFC), longitudinal slope (LS) and the presence of a junction (J). Separate prediction models for total crashes and for fatal and injury crashes only were considered. For curves it is shown that significant variables are L, 1/R and AADT, whereas for tangents they are L, AADT and junctions. The effect of rain precipitation was analysed on the basis of hourly rainfall data and assumptions about drying time. It is shown that a wet pavement significantly increases the number of crashes. The models developed in this paper for Italian motorways appear to be useful for many applications such as the detection of critical factors, the estimation of accident reduction due to infrastructure and pavement improvement, and the predictions of accidents counts when comparing different design options. Thus this research may represent a point of reference for engineers in adjusting or designing multilane roads.     

Effects of road geometry and traffic volumes on rural roadway accident rates

This paper revisits the question of the relationship between rural road geometric characteristics, accident rates and their prediction, using a rigorous non-parametric statistical methodology known as hierarchical tree-based regression. The goal of this paper is twofold: first, it develops a methodology that quantitatively assesses the effects of various highway geometric characteristics on accident rates and, second, it provides a straightforward, yet fundamentally and mathematically sound way of predicting accident rates on rural roads. The results show that although the importance of isolated variables differs between two-lane and multilane roads, 'geometric design' variables and pavement condition' variables are the two most important factors affecting accident rates. Further, the methodology used in this paper allows for the explicit prediction of accident rates for given highway sections, as soon as the profile of a road section is given.     

The evaluation of effects on driver behavior and accidents of concentrated general enforcement on interurban roads in Israel

The study deals with the evaluation of the effects of a new deployment of the National Traffic Police in Israel--a concentrated general enforcement on 700 km of interurban roads, which contain 60% of all rural accidents and about half of the severe accident locations. The enforcement project began in April 1997 and lasted for 1 year, aiming at a 10% reduction of severe accidents on those roads. The evaluation study consisted of three main parts: (a) monitoring of everyday police operations on the project roads; (b) periodic evaluation of the project's influence on drivers' behavior and attitudes; and (c) the evaluation of accident changes within the project area, at the end of the project year. Speed measurements, performed before the police project launch, demonstrated that, depending on road type, up to 85% of drivers violated the rural road speed limits. Two rounds of field observations, before and during the project, took place at 32 sites throughout the project area and comprised eight behavior types: turning performance; signaling while turning; compliance with 'stop' and 'yield' signs; safety belt use by drivers and front-seat passengers, at the intersections; 'keeping to the right' on dual carriageway roads; and 'not-crossing of the white separating line' at single carriageway roads. A comparison revealed a general reduction in violation rates of most behaviors, during-the-project, except for compliance with 'stop' signs and signaling. Concurrently, two rounds of driver surveys were performed which examined the project's influence on the drivers' attitudes towards the police enforcement effectiveness and risk connected with traffic rule violations. An improvement was identified in perceived general level of police activity, during the project, whereas a lower or similar risk of apprehension was attributed by drivers to most specific violations of the traffic rules. Three groups of indices of police activity were estimated monthly during the study: inputs; outputs; and efficiency indices, which characterized the police presence on the project roads, the citations produced and the usage rates of the vehicle fleet and the enforcement tools. Analyzing these indices, two periods in the project performance were determined, and three criteria were proposed to subdivide the project roads into two groups, according to the level of enforcement intensity. Both periods and enforcement levels, as well as geographic zone, were accounted for in the analysis of accident trends on the project roads. For the accident analysis, a statistical model combining the odds ratio and longitudinal methods, was developed and applied to the severe accident counts, all injury accidents and severe casualties. A statistically significant reduction in severe accidents and severe casualties, as opposed to the comparison group, was found on the highly enforced roads in the center of the country. At the same time, since the police project began, an increase in accidents was observed on most interurban roads, including the northern parts of the project area. However, it was noted that in four of the five project road groups the mean value of the odds ratio was much less than one. Thus, although the enforcement project did not attain its full purpose, it seemed to be a deterrent factor for the increasing accident trend that appeared that year on the interurban roads. The findings pointed out that the National Traffic Police did not exhaust its potential in the project's performance and needs more flexible enforcement and deployment tactics.     

The influence of heavy goods vehicle traffic on accidents on different types of Spanish interurban roads

This paper illustrates a methodology developed to analyze the influence of traffic conditions, i.e. volume and composition on accidents on different types of interurban roads in Spain, by applying negative binomial models. The annual average daily traffic was identified as the most important variable, followed by the percentage of heavy goods vehicles, and different covariate patterns were found for each road type. The analysis of hypothetical scenarios of the reduction of heavy goods vehicles in two of the most representative freight transportation corridors, combined with hypotheses of total daily traffic mean intensity variation, produced by the existence or absence of induced traffic gives rise to several scenarios. In all cases a reduction in the total number of accidents would occur as a result of the drop in the number of heavy goods transport vehicles, However the higher traffic intensity, resulting of the induction of other vehicular traffic, reduces the effects on the number of accidents on single carriageway road segments compared with high capacity roads, due to the increase in exposure. This type of analysis provides objective elements for evaluating policies that encourage modal shifts and road safety enhancements.     

Young driver accidents in the UK: the influence of age, experience, and time of day

Young drivers, especially males, have relatively more accidents than other drivers. Young driver accidents also have somewhat different characteristics to those of other drivers; they include single vehicle accidents involving loss of control; excess speed for conditions; accidents during darkness; accidents on single carriageway rural roads; and accidents while making cross-flow turns (i.e. turning right in the UK, equivalent to a left turn in the US and continental Europe). A sample of over 3000 accident cases was considered from midland British police forces, involving drivers aged 17-25 years, and covering a two year period. Four types of accident were analysed: right-turns; rear-end shunts; loss of control on curves; and accidents in darkness. Loss of control on curves and accidents in darkness were found to be a particular problem for younger drivers. It was found that cross-flow turn accidents showed the quickest improvement with increasing driver experience, whereas accidents occurring in darkness with no street lighting showed the slowest rate of improvement. 'Time of day' analyses suggested that the problems of accidents in darkness are not a matter of visibility, but a consequence of the way young drivers use the roads at night. There appears to be a large number of accidents associated with voluntary risk-taking behaviours of young drivers in 'recreational' driving.     

The effect of cycle lanes on the proximity between motor traffic and cycle traffic

An experiment collected proximity data of motor traffic overtaking cycle traffic on roads with and without cycle lanes using an instrumented bicycle. The work enhances previous research which has considered the riding position of the cyclist and whether or not the cyclist was helmeted, while controlling for vehicle type.The analysis shows that significantly wider passing distances are adopted by motorists in the condition without a 1.45 m cycle lane, with posted speed limits of 40 mph and 50 mph with a 9.5 m wide carriageway. These findings were not replicated for a similar width road with a posted speed limit of 30 mph and a 1.3 m cycle lane.The results suggest that in the presence of a cycle lane, drivers may be driving within the confines of their own marked lane with less recognition being given to the need to provide a comfortable passing distance to cycle traffic in the adjacent cycle lane.     

Methodology for fitting and updating predictive accident models with trend

Reliable predictive accident models (PAMs) (also referred to as Safety Performance Functions (SPFs)) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these ageing models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs, whether by re-calibration or by re-fitting. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models.     

A novel approach for analyzing severe crash patterns on multilane highways

This study presents a novel approach for analysis of patterns in severe crashes that occur on mid-block segments of multilane highways with partially limited access. A within stratum matched crash vs. non-crash classification approach is adopted towards that end. Under this approach crashes serve as units of analysis and it does not require aggregation of crash data over arterial segments of arbitrary lengths. Also, the proposed approach does not use information on non-severe crashes and hence is not affected by under-reporting of the minor crashes. Random samples of time, day of week, and location (i.e., milepost) combinations were collected for multilane arterials in the state of Florida and matched with severe crashes from the corresponding corridor to form matched strata consisting of severe crash and non-crash cases. For these cases, geometric design/roadside and traffic characteristics were derived based on the corresponding milepost locations. Four groups of crashes, severe rear-end, lane-change related, pedestrian, and single-vehicle/off-road crashes, on multilane arterials segments were compared separately to the non-crash cases. Severe lane-change related crashes may primarily be attributed to exposure while single-vehicle crashes and pedestrian crashes have no significant relationship with the ADT (Average Daily Traffic). For severe rear-end crashes speed limit, ADT, K-factor, time of day/day of week, median type, pavement condition, and presence of horizontal curvature were significant factors. The proposed approach uses general roadway characteristics as independent variables rather than event-specific information (i.e., crash characteristics such as driver/vehicle details); it has the potential to fit within a safety evaluation framework for arterial segments.     

Why do car drivers fail to give way to motorcycles at t-junctions?

Studies of accident statistics suggest that motorcyclists are particularly vulnerable to collisions with other vehicles which pull out of side roads onto a main carriageway, failing to give way to the approaching motorcycle. Why might this happen? The typical response of the car driver is that they looked in the appropriate direction but simply failed to see the motorcycle. To assess the visual skills of drivers in such scenarios we compared the behaviour of novice and experienced drivers to a group of dual drivers (with both car and motorcycle experience). Participants watched a series of video clips, displayed across three screens, depicting the approach to various t-junctions. On reaching the junction, participants had to decide when it was safe to pull out. Responses and eye movements were measured. The results confirmed that dual drivers had the safest responses at junctions, especially in the presence of conflicting motorcycles. On a range of visual measures both novice and experienced drivers appeared inferior to dual drivers, though for potentially different reasons. There were however no differences in the time it took all drivers to first fixate approaching motorcycles. Instead the differences appeared to be due to the amount of time spent looking at the approaching motorcycle. The experienced drivers had shorter gazes on motorcycles than cars, suggesting that they either process less salient motorcycles faster than cars, or that they terminated the gaze prematurely perhaps because they did not realise they were fixating a motorcycle. We argue that this is potential evidence for an oculomotor basis for Look But Fail To See errors.     

Updating outdated predictive accident models

Reliable predictive accident models (PAMs) (also referred to as safety performance functions (SPFs)) are essential to design and maintain safe road networks however, ongoing changes in road and vehicle design coupled with road safety initiatives, mean that these models can quickly become dated. Unfortunately, because the fitting of sophisticated PAMs including a wide range of explanatory variables is not a trivial task, available models tend to be based on data collected many years ago and seem unlikely to give reliable estimates of current accidents. Large, expensive studies to produce new models are likely to be, at best, only a temporary solution. This paper thus seeks to develop a practical and efficient methodology to allow currently available PAMs to be updated to give unbiased estimates of accident frequencies at any point in time. Two principal issues are examined: the extent to which the temporal transferability of predictive accident models varies with model complexity; and the practicality and efficiency of two alternative updating strategies. The models used to illustrate these issues are the suites of models developed for rural dual and single carriageway roads in the UK. These are widely used in several software packages in spite of being based on data collected during the 1980s and early 1990s. It was found that increased model complexity by no means ensures better temporal transferability and that calibration of the models using a scale factor can be a practical alternative to fitting new models.     

Safety evaluation of multilane arterials in Florida

Resurfacing is one of the more common construction activities on highways. While its effect on riding quality on any type of roadway is obviously positive; its impact on safety as measured in terms of crashes is far from obvious. This study examines the safety effects of the resurfacing projects on multilane arterials with partially limited access. Empirical Bayes method, which is one of the most accepted approaches for conducting before-after evaluations, has been used to assess the safety effects of the resurfacing projects. Safety effects are estimated not only in terms of all crashes but also rear-end as well as severe crashes (crashes involving incapacitating and fatal injuries). The safety performance functions (SPFs) used in this study are negative binomial crash frequency estimation models that use the information on ADT, length of the segments, speed limit and number of lanes. These SPFs are segregated by crash groups (all, rear-end, and severe), length of the segments being evaluated, and land use (urban, suburban, and rural). The results of the analysis show that the resulting changes in safety following resurfacing projects vary widely. Evaluating additional improvements carried out with resurfacing activities showed that all (other than sidewalk improvements for total crashes) of them consistently led to improvements in safety of multilane arterial sections. It leads to the inference that it may be a good idea to take up additional improvements if it is cost effective to do them along with resurfacing. It was also found that the addition of turning lanes (left and/or right) and paving shoulders were two improvements associated with a project's relative performance in terms of reduction in rear-end crashes.     

Red light running and close following behaviour at urban shuttle-lane roadworks

Roadworks (work zones) are a common feature of our urban environment. They have a considerable impact on reducing roadway capacity, causing interruptions and imposing substantial delays to road users, which in turn adds to the cost to society and adverse impact on road safety. Shuttle-lane (alternate one-way working) is one of the most commonly used traffic management arrangements at urban roadworks as most of the urban road network is built up from single carriageway.     

The influence of signs prompting motorists to yield before marked crosswalks on motor vehicle-pedestrian conflicts at crosswalks with flashing amber.

The purpose of this experiment was to evaluate the effects of signs reading "STOP HERE FOR PEDESTRIANS" alone and in conjunction with advance stop lines on pedestrian safety at multilane crosswalks with pedestrian-activated amber flashing lights. Motorist and pedestrian behaviors measured throughout this experiment included the occurrence of various types of motor vehicle-pedestrian conflicts; the distance that motorists stopped before the crosswalk when yielding to pedestrians; and the percentage of motorists yielding to pedestrians. The introduction of the sign alone 50 feet (15.15 m) before the crosswalk increased the distance before the crosswalk that motorists yielded to pedestrians and reduced the percentage of motor vehicle-pedestrian conflicts whether the flashing light was activated or not. The addition of the advance stop line was associated with further improvements in both measures.     

Titelbild: Mauerwerk 2/2016

The arched viaduct at Einsiedelstein near the Wermelskirchen junction between Leverkusen and Wuppertal was originally built in 1938 and has now been rebuilt with a new carriageway deck as part of the six‐lane widening of the Federal Autobahn A1. GRASSL Ingenieure performed the necessary structural recalculation of the bridge structure for the actions according to DIN Specialist Report 101 “Actions on Bridges” as well as the design for construction (see also the article on pp. 147–159). (photo: © wilfried‐dechau.de, design and structural design: www.grassl‐ing.de)     

The influence of road curvature on fatal crashes in New Zealand

Bends in roads can cause crashes but a recent study in the UK found that areas with mostly curved roads had lower crash rates than areas with straighter roads. This present study aimed to replicate the previous research in a different country. Variations in the number of fatal road crashes occurring between 1996 and 2005 in 73 territorial local authorities across New Zealand were modelled against possible predictors. The predictors were traffic flow, population counts and characteristics, car use, socio-economic deprivation, climate, altitude and road characteristics including four measures of average road curvature. The best predictors of the number of fatal crashes on urban roads, rural state highways and other rural roads were traffic flow, speed limitation and socio-economic deprivation. Holding significant factors constant, there was no evidence that TLAs with the most curved roads had more crashes than elsewhere. Fatal crashes on urban roads were significantly and negatively related to two measures of road curvature: the ratio of road length to straight distance and the cumulative angle turned per kilometre. Weaker negative associations on rural state highways could have occurred by chance. These results offer limited support to the suggestion that frequently occurring road bends might be protective.     

彩色城市地图的闭环反馈道路提取

为了实现彩色栅格地图道路的全自动提取,提出了一种闭环反馈提取彩色栅格地图道路的方法。在地图图像数学模型的基础上,根据地图中对象的颜色特征对地图图像进行规范化处理。在采用一些算法去除噪声后提取道路,对道路进行细化处理。依据道路和噪声的特征建立一些判据判断道路的正确性,把道路的提取变成了根据判据不断修正道路的循环过程,实现道路的全自动提取。试验结果表明了该方法具有较高的准确性、全自动化和通用性。     

Effects of transverse rumble strips on safety of pedestrian crosswalks on rural roads in China

The primary objective of this study is to evaluate the impacts of transverse rumble strips in reducing crashes and vehicle speeds at pedestrian crosswalks on rural roads in China. Using crash data reported at 366 sites, the research team conducted an observational before-after study using a comparison group and the Empirical Bayesian (EB) method to evaluate the effectiveness of transverse rumble strips in reducing crashes at pedestrian crosswalks. It was found that transverse rumble strips may reduce expected crash frequency at pedestrian crosswalks by 25%. The research team collected more than 15,000 speed observations at 12 sites. The speed data analysis results show that transverse rumble strips significantly reduce vehicle speeds in vicinity of pedestrian crosswalks on rural roads with posted speed limits of 60 km/h and 80 km/h. On average, the mean speed at pedestrian crosswalks declined 9.2 km/h on roads with a speed limit of 60 km/h; and 11.9 km/h on roads with a speed limit of 80 km/h. The 85th percentile speed declined 9.1 km/h on roads with a speed limit of 60 km/h; and 12.0 km/h on roads with a speed limit of 80 km/h. However, the speed reduction impacts were not found to be statistically significant for the pedestrian crosswalk on the road with a speed limit of 40 km/h. The study also looked extensively at the influence area of transverse rumble strips on rural roads. Speed profiles developed in this study show that the influence area of transverse rumble strips is generally less than 0.3 km.     

Traffic safety assessment and development of predictive models for accidents on rural roads in Egypt

This paper starts by presenting a conceptualization of indicators, criteria and accidents' causes that can be used to describe traffic safety. The paper provides an assessment of traffic safety conditions for rural roads in Egypt. This is done through a three-step procedure. First, deaths per million vehicle kilometers are obtained and compared for Egypt, three other Arab countries and six of the G-7 countries. Egypt stands as having a significantly high rate of deaths per 100 million vehicle kilometers. This is followed by compiling available traffic and accident data for five main rural roads in Egypt over a 10-year period (1990-1999). These are used to compute and compare 13 traffic safety indicators for these roads. The third step for assessing traffic safety for rural roads in Egypt is concerned with presenting a detailed analysis of accident causes. The paper moves on to develop a number of statistical models that can be used in the prediction of the expected number of accidents, injuries, fatalities and casualties on the rural roads in Egypt. Time series data of traffic and accidents, over a 10 years period for the considered roads, is utilized in the calibration of these predictive models. Several functional forms are explored and tested in the calibration process. Before proceeding to the development of these models three ANOVA statistical tests are conducted to establish whether there are any significant differences in the data used for models' calibration as a result of differences among the considered five roads.