Collision avoidance timing analysis of DSRC-based vehicles

Dedicated short-range communication (DSRC) has been used in prototyped vehicles to test vehicle-to-vehicle communication for collision avoidance. However, there is little study on how collision avoidance software should behave to best mitigate accident collisions. In this paper, we analyse the timing of events and how they influence software-based collision avoidance strategies. We have found that the warning strategies for collision avoidance are constrained by the timing of events such as DSRC communication latency, detection range, road condition, driver reaction and deceleration rate. With these events, we define two collision avoidance timings: critical time to avoid collision and preferred time to avoid collision, and they dictate the design of software-based collision avoidance systems.     

Simulation-based performance analysis and improvement of orthogonal frequency division multiplexing - 802.11p system for vehicular communications

In this study, the physical layer (PHY) of the upcoming vehicular communication standard IEEE 802.11p has been simulated in vehicle-to-vehicle situation through two different scenarios. IEEE 802.11p wireless access in vehicular environment defines modifications to IEEE 802.11 to support intelligent transportation systems applications. The standard is being considered as a promising wireless technology for enhancing transportation safety and provides safety-related services like collision avoidance and emergency breaking. At first, this includes data exchange between high-speed vehicles and between the vehicles and the roadside infrastructure in the licensed ITS band of 5.9 GHz. Performance analysis of PHY model has been evaluated into different propagation conditions (AWGN, Ricean and Rayleigh fading). In particular, bit error rate (BER) and signal to noise ratio for all the data rates have been estimated. Simulation results reveal that our system can efficiently mitigate inter-symbol interference and inter-carrier interference introduced by multi-path delay spread in our high mobility environment but against frequency-selective fading BER values are on to increase. To overcome this problem, the authors propose to use a different value of guard interval (3.2 μs). Our initial results indicate that the performance with the larger cyclic prefix outperforms the performance of the initial value in our mobile channel profiles. Moreover, the authors investigated in which way the Doppler spread affects the performance with regard to the transmission distance.     

Are SUVs dangerous vehicles?

This study was a population cohort study of all licensed passenger vehicles in New Zealand in the years 2005–2006. The objective of the study was to evaluate the effect on road safety of sports utility vehicles (SUVs) compared to other passenger vehicle types. Statistical models were fitted to the population of 2,996,000 vehicles of which 17,245 were involved in an injury crash. Controlling for distance driven, vehicle and owner characteristics, SUVs were found to be relatively safe vehicles in terms of injury crash involvement and in terms of the injury rate of their own occupants or other road users into which they crashed. Current research on SUV safety clearly shows them to be a road safety concern, but only once a collision occurs. The present study shows that SUVs in New Zealand have relatively few collisions compared to other passenger vehicle types, allowing for factors such as distance driven, some allowance for the type of driving exposure (via the owners’ addresses) and for owner age and gender. Overall, the vehicle type implicated most frequently in injury crashes and involving the highest rate of road injuries was sports cars, causing clearly the most harm per licensed vehicle. Instead of concerning themselves primarily with SUVs, the focus of road safety agencies should be on the relatively high crash risk of sports cars, which are clearly a road safety concern. Their high crash involvement rate and injury rate is likely to be largely due to the way they are driven rather than to inherent characteristics of the vehicles themselves.     

Traffic accident reduction by monitoring driver behaviour with in-car data recorders

People who are aware of being observed tend to modify their behaviour. This phenomenon could potentially be used to encourage individuals to behave more safely when driving if there were means of providing feedback to the drivers about their behaviour on the road. So-called 'vehicle data recorders' offer such a means of providing behavioural feedback by confronting drivers with their recorded driving actions. A field trial of a 'matched experimental/control group design with intervention' was planned with the objective of investigating whether this feedback mechanism would reduce the number of road traffic accidents in everyday driving conditions. In the study, seven experimental vehicle fleets were involved, which varied widely in terms of the kind of transport sector concerned, the type of vehicles used, and the traffic circumstances in which the vehicles are operated. Each fleet was matched with at least one control vehicle fleet, taking into account those relevant traffic safety characteristics. In total, accident and exposure data were collected for 840 vehicles of which 270 equipped with a recorder. During an observation period representing a total of about 3,100 vehicle years, these vehicles were involved in 1,836 road accidents. Analysis of the effects of the use of data recorders in these fleets resulted in an average estimated accident reduction of some 20%. The analysis shows that the actual savings vary depending on the transport sector involved and on the prior level of the fleet's safety record. Further studies are needed to identify the more promising application of such a use of traffic data recorders as a means of reducing road accidents.     

Factors contributing to the amount of vehicular damage resulting from collisions between four-wheel drive vehicles and passenger cars

This study examines the vehicular damage resulting from motor vehicle crashes involving four-wheel drive vehicles and passenger cars in the state of Oklahoma. In particular, the focus of the analysis is on differences in vehicular damage to passenger cars and four-wheel drive vehicles. Results indicate that passenger cars sustain significantly greater vehicular damage than four-wheel drive vehicles. In addition, several other factors significantly influence the level of damage resulting from collisions between four-wheel drive vehicles and passenger cars. Driver behavior or unsafe acts, represented by the rate of travel prior to the collision, failure to yield, failure to obey a stoplight or a stop sign, the consumption of alcohol and the use of drugs, also contributed to the amount of vehicular damage. In addition, results also indicate that the level of damage was influenced significantly by environmental factors, represented by a reduced intensity of light, wet or slippery roadways and the type of collision. The findings reinforce the importance of a number of policy initiatives that may reduce the vehicular damage resulting from collisions involving four-wheel drive vehicles and passenger cars. For example, the study indicates a need to initiate legislation that lowers the speed limit during dark and twilight hours, commits additional resources to road maintenance to reduce unsafe road conditions, and stimulates improvements in automotive design that provide better lateral protection to vehicles.     

Predicting the effect of various ISA penetration grades on pedestrian safety by simulation

Intelligent speed adaption (ISA) is one type of vehicle-based intelligent transportation systems (ITS), which warns and regulates driving speed according to the speed limits of the roads. Early field studies showed that ISA could reduce general mean speed levels and their variances in different road environments. This paper studies the effects of various ISA penetration grades on pedestrian safety in a single lane road. A microscopic traffic simulation tool, TPMA, was further developed and used to implement different ISA penetration grades. Momentary spot speed and traffic flow data are first logged in the traffic simulation for later prediction of pedestrian safety. Then a hypothetical vehicle–pedestrian collision model is extended from early researches in order to estimate two safety indicators: probability of collision, and risk of death. Finally, Monte Carlo method is applied iteratively to compute those safety indices. The computational result shows that raising ISA penetration in traffic flow will reduce both the probability of mid-block collision between vehicle and pedestrian and the risk of death in the collision accidents. Furthermore, the decrease of the risk of death will be more prominent than that of the collision probability according to this method.     

Micro-simulation of vehicle conflicts involving right-turn vehicles at signalized intersections based on cellular automata

At intersection, vehicles coming from different directions conflict with each other. Improper geometric design and signal settings at signalized intersection will increase occurrence of conflicts between road users and results in a reduction of the safety level. This study established a cellular automata (CA) model to simulate vehicular interactions involving right-turn vehicles (as similar to left-turn vehicles in US). Through various simulation scenarios for four case cross-intersections, the relationships between conflict occurrences involving right-turn vehicles with traffic volume and right-turn movement control strategies are analyzed. Impacts of traffic volume, permissive right-turn compared to red-amber-green (RAG) arrow, shared straight-through and right-turn lane as well as signal setting are estimated from simulation results. The simulation model is found to be able to provide reasonable assessment of conflicts through comparison of existed simulation approach and observed accidents. Through the proposed approach, prediction models for occurrences and severity of vehicle conflicts can be developed for various geometric layouts and traffic control strategies.     

考虑桥面风场等效气动效应的行车安全性分析

侧风作用下桥上通行车辆容易遭受行车安全问题。通过节段模型风洞试验,测试了主梁行车道位置上方一定高度范围内风场分布特性。基于车辆气动力和力矩等效的方法,采用等效风速和比例系数来考虑桥面气动绕流对车辆气动力特性的影响。在风-汽车-桥耦合振动研究的基础上,采用无量纲的侧倾和侧滑安全因子评价车辆的行车安全性,分析了风速和车速对不同类型车辆行车安全性的影响。结果表明:车辆的行车安全性随着风速和车速的增大而逐渐降低;桥面风场等效气动效应会降低集装箱车和旅行巴士的行车安全性,集装箱车RSF和SSF最大相对误差分别高达28.0%和184.3%。     

Risk evaluation by modeling of passing behavior on two-lane rural highways

Passing maneuver on rural two-lane highways is a complex task, which has a significant effect on capacity, level of service and safety. The maneuver is conditioned on the gap between two successive vehicles on the opposing lane. The minimum time to collision, defined as the remaining gap between the passing vehicle and the oncoming vehicle at the end of the passing process, expresses a measure of the risk involved in the passing maneuver.This paper develops a model that explains the minimum time to collision. The model formulation is based on the analysis of drivers’ passing decisions on two-lane rural highways using an interactive driving simulator. The simulator enables the collection of vehicle speeds and positions for different road and traffic scenarios. In addition to the driver simulator, participants responded to a questionnaire which collected information about their socio-demographic characteristics.The composed dataset was analyzed and processed to develop a model that predicts the risk associated with the passing behavior. Tobit regression models were found to be more suitable, in comparison to ordinary least square models and Hazard-based Duration models. The explanatory variables tested represent road geometry, traffic conditions and drivers’ characteristics. It was found that while the traffic related variables had the most important effect on the measure of risk chosen, factors related to the geometric design and the driver characteristics also had a significant contribution.     

Pollutant emissions from passenger cars in traffic congestion situation in the State of Kuwait: options and challenges

Rapid population growth in Kuwait, accompanied with rising standard of living, has resulted in a sweeping increase in the use of passenger vehicles for transportation. Consequently, deterioration of ambient air quality near major roadways has become an issue of public concern. The knowledge of real world road vehicle emission factors is an essential element to the development of any strategy aimed at the reduction of air pollution in urban areas. This work focuses on investigating exhaust emission pollutants from passenger cars for idle and slow acceleration (stop-and-go) traffic conditions. We found that vehicle emissions are minimal during idle mode for all vehicle categories. However, it was interesting to observe that during the slow acceleration mode HC and CO emissions increased for light vehicles with relatively high mileage (higher than 40,000?km). We can conclude from this study that with the growing vehicle ownership, and congestion it causes, the vehicular exhaust emissions is a major sources of air pollution in densely populated centers in the state of Kuwait, where idle and stop-and-go driving cycle is a common occurrence.     

Road safety issues for bus transport management

Because of the low percentage of crashes involving buses and the assumption that public transport improves road safety by reducing vehicular traffic, public interest in bus safety is not as great as that in the safety of other types of vehicles. It is possible that less attention is paid to the significance of crashes involving buses because the safety level of bus systems is considered to be adequate.     

Traffic violations in Guangdong Province of China: Speeding and drunk driving

The number of speeding- and drunk driving-related injuries in China surged in the years immediately preceding 2004 and then began to decline. However, the percent decrease in the number of speeding and drunk driving incidents (decrease by 22%) is not proportional to the corresponding percent decrease in number of automobile accident-related injuries (decrease by 47%) from the year 2004 to 2010 (Traffic Management Bureau, Ministry of Public Security, Annual Statistical Reports on Road Traffic Accidents). Earlier studies have established traffic violations as one of the major risks threatening road safety. In this study, we examine in greater detail two important types of traffic violation events, speeding and drunk driving, and attempt to identify significant risk factors associated with these types of traffic violations. Risk factors in several different dimensions, including driver, vehicle, road and environmental factors, are considered. We analyze the speeding (N = 11,055) and drunk driving (N = 10,035) data for the period 2006–2010 in Guangdong Province, China. These data, obtained from the Guangdong Provincial Security Department, are extracted from the Traffic Management Sector-Specific Incident Case Data Report and are the only comprehensive and official source of traffic accident data in China. Significant risk factors associating with speeding and drunk driving are identified. We find that several factors are associated with a significantly higher probability of both speeding and drunk driving, particularly male drivers, private vehicles, the lack of street lighting at night and poor visibility. The impact of other specific and unique risk factors for either speeding or drunk driving, such as hukou, road type/grades, commercial vehicles, compulsory third party insurance and vehicle safety status, also require particular attention. Legislative or regulatory measures targeting different vehicle types and/or driver groups with respect to the various driver, vehicle, road and environmental risk factors can subsequently be devised to reduce the speeding and drunk driving rates. As the country with the highest number of traffic accident fatalities in the world, applying these findings in workable legislation and enforcement to reduce speeding and drunk driving rates will save tens of thousands of lives.     

Work-related road traffic collisions in the UK

Road traffic collisions while at work are the single largest cause of occupational fatality in the United Kingdom. Work-related road collisions do not comprise a homogenous group, but take many forms, encompassing the use of varying types of vehicle used for diverse purposes. A sample of over 2000 collision cases was considered, over 1000 in detail, from UK police forces, involving drivers/workers of all ages, and covering the years 1996-2004 inclusive. There were three key findings. (1) There were six main classes of collision-involved vehicles. These were company cars, vans/pickups, large goods vehicles (LGVs), buses (PCVs or ‘passenger carrying vehicles’), taxis/minicabs, and emergency vehicles (police, fire/rescue and ambulance). (2) The drivers of company cars, vans/pickups, and large goods vehicles (LGVs) all appeared to have a high ‘blameworthiness ratio’ in their collision involvement. Company car drivers showed excess speed as a causal factor, whereas van drivers showed more observational failures, and LGV drivers showed more fatigue and vehicle defects as factors. (3) The drivers of buses (PCVs), taxis/minicabs, and emergency vehicles showed a low ‘blameworthiness ratio’ in their collision involvement. Their problems seemed to be primarily with the other drivers/parties with whom they share the road. While they made a variety of mistakes or errors, they were more likely to become the victim of another party's mistake or error.     

Dynamic resource allocation for supporting real-time multimedia applications in IEEE 802.15.3 WPANs

The IEEE 802.15.3 medium access control (MAC) protocol is an emerging standard for high-rate wireless personal area networks (WPANs), especially for supporting high-quality real-time multimedia applications. Despite defining quality of service (QoS) signalling mechanisms for interoperability between devices, IEEE 802.15.3 does not specify resource allocation algorithms that are left to manufacturers. To guarantee the QoS of real-time variable bit rate (VBR) videos and utilise the radio resource efficiently, the authors propose a dynamic resource allocation algorithm. The proposed bandwidth allocation algorithm is based on a novel traffic predictor. Recently, the variable step-size normalised least mean square (VSSNLMS) algorithm was employed for on-line traffic prediction of VBR videos. However, the performance of the VSSNLMS algorithm significantly degrades due to the abrupt traffic variation occurring at the scene boundary. To tackle this problem, the authors design a novel traffic predictor based on a simple scene detection algorithm and the VSSNLMS algorithm. Analyses using real-life MPEG video traces indicate that the proposed traffic predictor significantly outperforms the VSSNLMS algorithm with respect to the prediction error. The performance of the proposed bandwidth allocation algorithm is also investigated by comparing several existing algorithms. Simulation results demonstrate that the proposed bandwidth allocation algorithm surpasses other mechanisms in terms of channel utilisation, buffer usage and packet loss rate.     

悬挂式人行桥基频估算及考虑车致振动效应的行人舒适性评价

将人行桥作为车行主桥的悬挂结构,形成一个组合式桥梁,共同解决人车通行问题,然而这种结构形式在主桥车辆荷载激励下人行桥的振动舒适性还有待研究。首先推导了悬挂式人行桥的基频估算公式并通过有限元计算进行了验证,研究表明悬挂式人行桥的基频很大程度上取决于车行主桥的自振特性。采用分离迭代法对某悬挂式人行桥的车致振动响应进行了分析,结果表明车行桥路面粗糙度、车速、车流密度等都会显著影响车辆通过时桥梁的振动响应,车致振动引起的人行桥跨中竖向峰值加速度可达到仅人行激励引起的相应值的一半以上,悬挂式人行桥行人舒适性评价中应考虑会降低其舒适度的车致振动效应的影响。     

An evaluation of the specific deterrent effects of vehicle impoundment on suspended, revoked, and unlicensed drivers in California

There have been a number of studies conducted during the past two decades that convincingly demonstrate that license suspension and revocation are some of the most effective countermeasures currently available for attenuating the traffic safety risk of problem drivers. At the same time, it is also known that most suspended/revoked (S/R) drivers violate their illegal driving status and continue to drive, accruing traffic convictions and becoming involved in crashes. In an attempt to strengthen license actions and to better control S/R and unlicensed drivers, California enacted two laws effective January 1995 which provide for the impoundment and forfeiture of vehicles driven by S/R and unlicensed drivers. The study described in this paper evaluates the impact of vehicle impoundment on the 1-year subsequent driving behavior of S/R and unlicensed drivers who experience this sanction. The results show that drivers with no prior convictions for driving while S/R or unlicensed whose vehicles were impounded have, relative to similar drivers whose vehicles were not impounded: 23.8% fewer driving while suspended/revoked or unlicensed convictions; 18.1% fewer traffic convictions; and 24.7% fewer crashes. The differences between the impound and no-impound groups are even larger when the driving records of repeat offenders (i.e. drivers with prior driving-while-S/R or unlicensed convictions) are examined. Repeat offenders whose vehicles are impounded have 34.2% fewer driving-while-S/R or unlicensed convictions, 22.3% fewer traffic convictions and 37.6% fewer crashes. These findings provide strong support for impounding vehicles driven by S/R and unlicensed drivers.     

Hit-and-run crashes in urban river-crossing road tunnels

Hit-and-run crashes are a relatively infrequent but severe offense worldwide because the identification and emergency rescue of victims is delayed, which increases the injury severities and the mortality rate. However, no studies have been conducted on hit-and-run crashes in urban river-crossing road tunnels (URCRTs), which can greatly threaten the safety of motorists driving in the tunnels. This study, which employs a dataset of vehicle crashes that happened in thirteen urban road tunnels traversing the Huangpu River, established a binary logistic regression model to identify thirteen factors that contribute to escaping after crashes in Shanghai related to the offending drivers, the vehicular and environmental conditions, the tunnel characteristics and crash information. Among the thirty-five variables considered, this study found that a perpetrator's tendency to leave the crash scene without reporting an accident was higher at night, in the tunnel exit, near to or in short tunnels, when a two-wheeled vehicle or heavy goods vehicle (HGV) was involved and when alcohol was involved. While a perpetrator was more likely to remain on the scene in the tunnel entrance, on a rainy day, in a rear end collision, when a bus was involved, in a single vehicle or a multi-vehicle accident. Based on these findings, several countermeasures for better supervision and hit-and-run prevention are proposed.     

风汽车桥梁系统耦合振动及行车安全性分析

强风不仅是长大桥梁设计的控制性因素,而且直接影响到桥上车辆的运行安全。将自然风、公路车辆、桥梁作为一个统一的相互作用系统,在风-汽车-桥梁系统耦合振动分析的基础上,针对车辆侧倾事故和侧滑事故的评判准则,采用概率统计方法提高了风致车辆事故分析的可靠性。结合工程实例对强风作用下桥梁的动力响应和车辆的运行安全性进行了分析。计算得到了给定的车速条件下厢式货车的侧倾临界风速及干、湿、雪、冰四种路况情况下的侧滑临界风速,提出了适用于交通安全策略管理的强风天气条件下桥上车辆限速标准。     

Relationship between crash rate and hourly traffic flow on interurban motorways

This paper describes the relationship between crash incidence rates and hourly traffic volume and discusses the influence of traffic on crash severity, based on observations made on 2000 km of French interurban motorways over 2 years. Incidence rates involving property damage-only crashes and injury-crashes are highest when traffic is lightest (under 400 vehicles/h). These incidence rates are at their lowest when traffic flows at a rate of 1000-1500 vehicles/h. For heavier traffic flows, crash incidence rates increase steadily as traffic increases on 2- and 3-lane motorways and inflect on 2-lane motorways when traffic increases to a level of 3000 vehicles/h. For an equivalent light traffic level, the number of crashes is higher on three-lane than on 2-lane motorways and higher at weekends (when truck traffic is restricted) than on weekdays. In heavy traffic, the number of crashes is higher on weekdays. We found no significant difference between the number of daytime and night-time crashes, whatever the traffic. No difference was observed in crash severity by number of lanes or period in the week for a given level of traffic. However, severity is greater at night and when hourly traffic is light. Compared to the number of vehicles on the road, light traffic is a safety problem in terms of frequency and severity, and road safety campaigns targeting motorway users to influence their behavior in these driving conditions should be introduced.     

Effective transmission opportunity allocation scheme for real-time variable bit rate traffic flows with different delay bounds

The medium access control of IEEE 802.11e defines a novel coordination function, namely, hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate traffic, packet loss may occur seriously. The authors propose a TXOP allocation scheme to efficiently allocate bandwidth and meet the QoS requirements in terms of both delay bound and packet loss probability. To achieve high bandwidth efficiency, the authors take advantage of not only intra-flow multiplexing gain of traffic flows with large delay bounds, but also inter-flow multiplexing gain of multiple traffic flows with different delay bounds. According to numerical results obtained by computer simulations, the proposed TXOP allocation scheme results in much higher bandwidth efficiency than previous algorithms under the same constraints of delay bounds and packet loss probability.