Safety performance functions for crash severity on undivided rural roads

The objective of this paper is to explore the effect of the road features of two-lane rural road networks on crash severity. One of the main goals is to calibrate Safety Performance Functions (SPFs) that can predict the frequency per year of injuries and fatalities on homogeneous road segments. It was found that on more than 2000 km of study-road network that annual average daily traffic, lane width, curvature change rate, length, and vertical grade are important variables in explaining the severity of crashes. A crash database covering a 5-year period was examined to achieve the goals (1295 injurious crashes that included 2089 injuries and 235 fatalities). A total of 1000 km were used to calibrate SPFs and the remaining 1000 km reflecting the traffic, geometric, functional features of the preceding one were used to validate their effectiveness. A negative binomial regression model was used. Reflecting the crash configurations of the dataset and maximizing the validation outcomes, four main sets of SPFs were developed as follows: (a) one equation to predict only injury frequency per year for the subset where only non-fatal injuries occurred, (b) two different equations to predict injury frequency and fatality frequency per year per sub-set where at least one fa tality occurred together with one injury, and (c) only one equation to predict the total frequency per year of total casualties correlating accurate percentages to obtain the final expected frequency of injuries and fatalities per year on homogeneous road segments. Residual analysis confirms the effectiveness of the SPFs.     

Development of adjustment functions to assess combined safety effects of multiple treatments on rural two-lane roadways

Numerous studies have attempted to evaluate the safety effectiveness of specific single treatment on roadways by estimating crash modification factors (CMFs). However, there is a need to also assess safety effects of multiple treatments since multiple treatments are usually simultaneously applied to roadways. Due to the lack of sufficient CMFs of multiple treatments, the Highway Safety Manual (HSM) provides combining method for multiple CMFs. However, it is cautioned in the HSM and related sources that combined safety effect of multiple CMFs may be over or under estimated. Moreover, the literature did not evaluate the accuracy of the combining method using CMFs obtained from the same study area. Thus, the main objectives of this research are: (1) to estimate CMFs and crash modification functions (CM Functions) for two single treatments (shoulder rumble strips, widening (1–9 ft) shoulder width) and combination (installing shoulder rumble strips + widening shoulder width) using the observational before–after with empirical Bayes (EB) method and (2) to develop adjustment factors and functions to assess combined safety effects of multiple treatments based on the accuracy of the combined CMFs for multiple treatments estimated by the existing combining method. Data was collected for rural two-lane roadways in Florida and Florida-specific safety performance functions (SPFs) were estimated for different crash types and severities. The CM Functions and adjustment functions were developed using linear and nonlinear regression models. The results of before–after with EB method show that the two single treatments and combination are effective in reducing total and SVROR (single vehicle run-off roadway) crashes. The results indicate that the treatments were more safety effective for the roadway segments with narrower original shoulder width in the before period. It was found that although the CMFs for multiple treatments (i.e., combination of two single treatments) were generally lower than CMFs for single treatments, they were getting similar to the roadway segments with wider shoulder width. The findings indicate that the combined safety effects of multiple treatments using HSM combining method are mostly over-estimated and the accuracy of HSM combining method vary based on crash types and severity levels. Therefore, it is recommended to develop and apply the adjustment factors and functions to predict the safety effects of multiple treatments when the HSM combining method is used.     

Safety effects of unsignalized superstreets in North Carolina

Arterials across the United States are experiencing far too many collisions. Agencies tasked with improving these arterials have few available effective solutions. Superstreets, called restricted crossing u-turns by the Federal Highway Administration (FHWA), are part of a menu of unconventional arterial intersection designs that may provide a promising solution. Up to this point, there is little valid information available on the safety effects of superstreets, as study results have been from basic analyses that only account for traffic volume changes. The purpose of this research was to determine the safety effects of the unsignalized superstreet countermeasure on existing arterials in North Carolina.     

Safety effects of wider edge lines on rural,two-lane highways

Although it is generally expected that wider lines will have a positive effect on vehicle safety, there have not been any convincing evidence based on the crash data analysis, partly because of the lack of relevant data. In this paper, the safety effect of wider edge lines was examined by analyzing crash frequency data for road segments with and without wider edge lines. The data from three states, Kansas, Michigan, and Illinois, have been analyzed. Because of different nature of data from each state, a different statistical analysis approach was employed for each state: an empirical Bayes, before-after analysis of Kansas data, an interrupted time series design and generalized linear segmented regression analysis of Michigan data, and a cross sectional analysis of Illinois data. Although it is well-known that causation is hard to establish based on observational studies, the results from three extensive statistical analyses all point to the same findings. The consistent findings lend support to the positive safety effects of wider edge lines installed on rural, two-lane highways.     

Exploration and comparison of crash modification factors for multiple treatments on rural multilane roadways

As multiple treatments (or countermeasures) are simultaneously applied to roadways, there is a need to assess their combined safety effects. Due to a lack of empirical crash modification factors (CMFs) for multiple treatments, the Highway Safety Manual (HSM) and other related studies developed various methods of combining multiple CMFs for single treatments. However, the literature did not evaluate the accuracy of these methods using CMFs obtained from the same study area. Thus, the main objectives of this research are: (1) develop CMFs for two single treatments (shoulder rumble strips, widening shoulder width) and one combined treatment (shoulder rumble strips + widening shoulder width) using before–after and cross-sectional methods and (2) evaluate the accuracy of the combined CMFs for multiple treatments estimated by the existing methods based on actual evaluated combined CMFs. Data was collected for rural multi-lane highways in Florida and four safety performance functions (SPFs) were estimated using 360 reference sites for two crash types (All crashes and Single Vehicle Run-off Roadway (SVROR) crashes) and two severity levels (all severity (KABCO) and injury (KABC)).     

Safety impact of Gateway Monuments

Gateway Monuments are free standing roadside structures or signage that communicate the name of a city, country or township to motorists. The placement of such monuments within state-controlled right-of-way is a relatively recent occurrence in California. As a result, the California Department of Transportation (Caltrans) initiated research to quantify the impacts that this type of signage may or may not have on crashes in their vicinity. To date, no specific research has examined the impact such features have on crashes. To determine whether these features impacted safety, the before–after study method using the Empirical Bayes technique was used, with reference groups and Safety Performance Functions adapted from existing studies, eliminating the need to calibrate new models. Results indicated that, on an individual basis, no deterioration in safety was observed at any monument site. When all sites were examined collectively (using two different scenarios), the calculated index of effectiveness values were 0.978 and 0.680, respectively, corresponding to 2.2% and 32.0% reductions in crashes. In addition to the EB method, naïve study methods (with and without AADT taken into account) were applied to the study data. Results (crash reductions) from these methods also showed that the presence of Gateway Monuments did not have negative impact on traffic safety. However, the use of EB technique should be very careful employed when adopting reference groups from different jurisdictions, as these may affect the validity of EB results. In light of these results, Caltrans may continue to participate in the Gateway Monument Program at its discretion with the knowledge that roadway safety is not impacted by monuments.     

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.     

Effects on road safety of new urban arterial roads

This paper presents an evaluation of the effects on road safety of new urban arterial roads in Oslo, Norway, and a synthesis of evidence from similar studies that have evaluated the safety effects of new urban arterial roads in other cities. A before-and-after study was made of four urban arterial road projects in Oslo. The study controlled for general accident trends in Oslo and for regression-to-the-mean. A statistically non-significant reduction of 9% in the number of injury accidents was found for all four projects combined. The effects on safety of new urban arterial roads were found to vary, depending on whether a new arterial road was built, or an existing arterial road upgraded by means of lane additions and reconstruction of junctions to interchanges. New arterial roads tend to induce more traffic, which tends to offset the benefits of a lower accident rate on the new roads. The results for other cities are very consistent with those for Oslo. For a total of seven cases in which new arterial roads were built, a statistically non-significant reduction of 1% in the number of injury accidents was found. Two cases that involved lane additions and converting at-grade junctions to interchanges resulted in a mean accident reduction of 51%, which was highly significant. On the average, the nine arterial road projects from which evidence was summarised resulted in a net induced traffic of 16%, and a net reduction in accident rate (accidents per million vehicle kilometres) of 18%. These effects almost cancel each other, leading to a very small net change in the expected number of accidents.     

An engineering fragmentation model for the impact of spherical projectiles on thin metallic plates

In this paper, an engineering fragmentation model is presented for the case of hypervelocity impact of a spherical projectile on a thin bumper plate at normal incidence. The range of impact velocities covered is the solid fragmentation regime up to the limits of complete melting of projectile and target material. The model was developed for an axisymmetric fragment cloud by consideration of the conservation laws for mass, momentum, and energy, as well as making a few assumptions on the morphology of the cloud. The fragment cloud is modeled discretely, i.e. each particle of the fragment cloud is considered separately in the analytical calculation. The model consists of mainly analytical relationships and a few empirical fit functions, where no analytical formulation was available. The model distinguishes between fragments originating from the projectile and fragments originating from the bumper plate. The projectile fragments are split into the central fragment and spall fragments. An exponential distribution function is assumed for the mass distribution of the projectile's spall fragments. The fragments from the bumper are assumed to have a uniform mass. All fragments are assumed to be of spherical shape. The fragmentation model was applied and calibrated during experiments, in which Al spheres impact on thin Al plates. The calibration experiments, performed using a two-stage light gas gun, were in the range of impact velocities between 4.8 and 6.7 km/s. In this velocity range, the model was calibrated against residual velocities measured and fragment mass distribution, which was indirectly determined by measuring the crater depth distributions in rear walls.     

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.     

A comparative analysis of hotspot identification methods

The identification of crash hotspots is the first step of the highway safety management process. Errors in hotspot identification may result in the inefficient use of resources for safety improvements and may reduce the global effectiveness of the safety management process. Despite the importance of using effective hotspot identification (HSID) methods, only a few researchers have compared the performance of various methods. In this research, seven commonly applied HSID methods were compared against four robust and informative quantitative evaluation criteria. The following HSID methods were compared: crash frequency (CF), equivalent property damage only (EPDO) crash frequency, crash rate (CR), proportion method (P), empirical Bayes estimate of total-crash frequency (EB), empirical Bayes estimate of severe-crash frequency (EBs), and potential for improvement (PFI). The HSID methods were compared using the site consistency test, the method consistency test, the total rank differences test, and the total score test. These tests evaluate each HSID method's performance in a variety of areas, such as efficiency in identifying sites that show consistently poor safety performance, reliability in identifying the same hotspots in subsequent time periods, and ranking consistency. To evaluate the HSID methods, five years of crash data from the Italian motorway A16 were used.The quantitative evaluation tests showed that the EB method performs better than the other HSID methods. Test results highlight that the EB method is the most consistent and reliable method for identifying priority investigation locations. The EB expected frequency of total-crashes (EB) performed better than the EB expected frequency of severe-crashes (EBs), although the results differed only slightly when the number of identified hotspots increased. The CF method performed better than other HSID methods with more appealing theoretical arguments. In particular, the CF method performed better than the CR method. This result is quite alarming, since many agencies use the CR method. The PFI and EPDO methods were largely inconsistent. The proportion method performed worst in all of the tests. Overall, these results are consistent with the results of previous studies.The identification of engineering countermeasures that may reduce crashes was successful in all of the hotspots identified with the EB method; this finding shows that the identified hotspots can also be corrected.The advantages associated with the EB method were based on crash data from one Italian motorway, and the relative performances of HSID methods may change when using other crash data. However, the study results are very significant and are consistent with earlier findings. To further clarify the benefits of the EB method, this study should be replicated in other countries. Nevertheless, the study results, combined with previous research results, strongly suggest that the EB method should be the standard in the identification of hotspots.     

Assessing the safety effects of multiple roadside treatments using parametric and nonparametric approaches

This study evaluates the safety effectiveness of multiple roadside elements on roadway segments by estimating crash modification factors (CMFs) using the cross-sectional method. To consider the nonlinearity in crash predictors, the study develops generalized nonlinear models (GNMs) and multivariate adaptive regression splines (MARS) models. The MARS is one of the promising data mining techniques due to its ability to consider the interaction impact of more than one variables and nonlinearity of predictors simultaneously. The CMFs were developed for four roadside elements (driveway density, poles density, distance to poles, and distance to trees) and combined safety effects of multiple treatments were interpreted by the interaction terms from the MARS models. Five years of crash data from 2008 to 2012 were collected for rural undivided four-lane roadways in Florida for different crash types and severity levels. The results show that the safety effects decrease as density of driveways and roadside poles increase. The estimated CMFs also indicate that increasing distance to roadside poles and trees reduces crashes. The study demonstrates that the GNMs show slightly better model fitness than negative binomial (NB) models. Moreover, the MARS models outperformed NB and GNM models due to its strength to reflect the nonlinearity of crash predictors and interaction impacts among variables under different ranges. Therefore, it can be recommended that the CMFs are estimated using MARS when there are nonlinear relationships between crash rate and roadway characteristics, and interaction impacts among multiple treatments.     

Effects on speed and safety of point-to-point speed enforcement systems: Evaluation on the urban motorway A56 Tangenziale di Napoli

In this paper, we evaluated the effects on speed and safety of the point-to-point (P2P) speed enforcement system activated on the urban motorway A56 in Italy. The P2P speed enforcement is a relatively new approach to traffic law enforcement that involves the calculation of the average speed over a section. To evaluate the speed effects, we performed a before–after analysis of speed data investigating also effects on non-compliance to speed limits. To evaluate the safety effects, we carried out an empirical Bayes observational before-and-after study.     

Examining the effects of site selection criteria for evaluating the effectiveness of traffic safety countermeasures

The primary objective of this paper is to describe how site selection effects can influence the safety effectiveness of treatments. More specifically, the goal is to quantify the bias for the safety effectiveness of a treatment as a function of different entry criteria as well as other factors associated with crash data, and propose a new method to minimize this bias when a control group is not available. The study objective was accomplished using simulated data. The proposed method documented in this paper was compared to the four most common types of before–after studies: the Naïve, using a control group (CG), the empirical Bayes (EB) method based on the method of moment (EB_MM), and the EB method based on a control group (EB_CG). Five scenarios were examined: a direct comparison of the methods, different dispersion parameter values of the Negative Binomial model, different sample sizes, different values of the index of safety effectiveness (θ$\theta$), and different levels of uncertainty associated with the index. Based on the simulated scenarios (also supported theoretically), the study results showed that higher entry criteria, larger values of the safety effectiveness, and smaller dispersion parameter values will cause a larger selection bias. Furthermore, among all methods evaluated, the Naïve and the EB_MM methods are both significantly affected by the selection bias. Using a control group, or the EB_CG, can mutually eliminate the site selection bias, as long as the characteristics of the control group (truncated data for the CG method or the non-truncated sample population for the EB_CG method) are exactly the same as for the treatment group. In practice, finding datasets for the control group with the exact same characteristics as for the treatment group may not always be feasible. To overcome this problem, the method proposed in this study can be used to adjust the Naïve estimator of the index of safety effectiveness, even when the mean and dispersion parameter are not properly estimated.     

爆破振动对临近尾矿坝的安全影响分析

为了探求采场爆破对临近尾矿库坝体稳定性的影响程度,进行了4次不同爆破参数采场爆破实验,并对爆破实验的振动影响进行监测。采用萨道夫斯基爆破振动经验公式计算爆破振动速度,为了得到更准确、更可靠的k、α值,对监测数据进行线性拟合,变换出适合该矿的萨道夫斯基爆破振动公式;根据该公式对不同振动速度控制标准下的起爆炸药量和最小安全距离关系进行了预测,对不同振动速度控制标准下的安全距离与允许最大起爆药量进行了估算。研究结果对矿山露天爆破最大药量和安全距离的选取具有一定的现场指导意义。     

The impact of perceptual treatments on driver's behavior: From driving simulator studies to field tests—First results

Our study focused on the lateral position of drivers in relation to risk on rural crest vertical curves, using a field site proposed by a local operator of the French road network (Conseil Général de Maine-et-Loire, 49). The final goal was to test one road treatment on this field site. The study consisted of three stages. The first, using driving simulators, selected two perceptual treatments (i.e., rumble strips on both sides of the centerline and sealed shoulders) from five that were tested in order to help drivers maintain lateral control when driving on crest vertical curves. The rumble strips were installed first on the field site.     

The effects of speed enforcement with mobile radar on speed and accidents. An evaluation study on rural roads in the Dutch province Friesland

In an evaluation study, the effects of targeted speed enforcement on speed and road accidents were assessed. Enforcement was predominantly carried out by means of mobile radar and focused on rural non-motorway roads. Information and publicity supported the enforcement activities. The evaluation covered a period of 5 years of enforcement. The speed data of these 5 years and the year preceding the enforcement project showed a significant decrease in mean speed and the percentage speed limit violators over time. The largest decrease was found in the first year of the enforcement project and in the fourth year of the project, when the enforcement effort was further intensified. There were similar decreases in speeding at both the enforced roads and at the nearby comparison roads that were not subjected to the targeted speed enforcement project, which may be explained by spillover effects. The best estimate for the safety effect of the enforcement project is a reduction of 21% in both the number of injury accidents and the number of serious casualties. This was based on comparison between the number of accidents/casualties during the enforcement project (5 years) and and the 8 preceding years on the enforced roads and at all other roads outside urban areas in the same region.     

护栏碰撞中车体加速度敏感性分析

碰撞参数在试验组织中会产生误差,为了解车体冲击加速度指标对碰撞参数的敏感程度,建立车辆碰撞某组合式护栏有限元仿真模型,运用碰撞试验对有限元模型的可靠性进行验证后,进行敏感性分析。结果表明,仿真与碰撞试验结果相符,验证了仿真方法的可靠性;车体冲击加速度指标对车辆质量、碰撞角度与碰撞速度参数的敏感度系数分别为-0.58、1.63、4.18,碰撞速度是影响车体冲击加速度的最敏感因素。研究成果为制定碰撞试验误差范围有指导意义。     

岩体软弱夹层对爆破震动信号影响的试验研究

岩体中的软弱夹层对爆破震动信号有明显的影响。在南宁市郊区一采石场进行了软弱夹层影响爆破震动信号的试验,在试验中采用了无线网络控制的爆破震动信号测量系统,并针对以前试验中的不足,改变了药包起爆顺序,试验结果表明：在软弱夹层上方爆破的震动信号时域曲线比较规整简单,频域曲线主峰非常突出明显且高频部分很少;在软弱夹层处及其下方爆破的震动信号时域曲线相对软弱层上方要复杂的多,频域曲线叠加了较多的高频成分,曲线中呈现多峰特性。依据试验结果提出了采用爆破震动信号识别软弱夹层的近似简便方法,并对该法的原理和适用性进行了分析