Developmental differences in auditory detection and localization of approaching vehicles

Pedestrian safety is a significant problem in the United States, with thousands being injured each year. Multiple risk factors exist, but one poorly understood factor is pedestrians’ ability to attend to vehicles using auditory cues. Auditory information in the pedestrian setting is increasing in importance with the growing number of quieter hybrid and all-electric vehicles on America's roadways that do not emit sound cues pedestrians expect from an approaching vehicle. Our study explored developmental differences in pedestrians’ detection and localization of approaching vehicles. Fifty children ages 6–9 years, and 35 adults participated. Participants’ performance varied significantly by age, and with increasing speed and direction of the vehicle's approach. Results underscore the importance of understanding children's and adults’ use of auditory cues for pedestrian safety and highlight the need for further research.     

Errors in motion processing amongst older drivers may increase accident risk

Accident statistics highlight that older drivers are more frequently involved in right-of-way collisions than younger drivers. Accurately gauging vehicle speed is critical for judgement of when to pull out from a junction safely in front of oncoming traffic. We used psychophysical methods to measure drivers’ ability to discriminate between different rates of looming presented by vehicles approaching at different speeds. We demonstrate that sensitivity to approach speed reduces by between 2.8 and 3.4 mph, dependent upon vehicle type, for every decade that age increases. We show that perceptual limitations for drivers over the age of 75 years can lead to a 50% reduction in time available to perform traffic manoeuvres, which may contribute in part to their overrepresentation in casualty statistics at junction. Results are discussed in terms of implications for road safety policy.     

Motorcycle and scooter speeds approaching urban intersections

Five urban, uncontrolled T-intersections known to be motorcycle crash ‘black spots’ were monitored using instrumentation and a roadside observer. Two sets of twelve-hour observations were collected for each site (N ≈ 100,000). Instrumentation recorded the ‘events’ of vehicles passing to measure, speed, direction, lane position, vehicle type (broadly characterised) and headway. Observers further recorded times of bicycle events, type of motorcycle (scooters or motorcycles), the behaviour of motorcycles and the use of ‘high conspicuity’ gear such as clothing or helmets. Results establish that motorcycles travel around 10% faster than the other traffic (car mean speed = 34.97 km/h), with motorcycles travelling on average 3.3 km/h faster than cars. Motorcycles were 3.4 times more likely to be exceeding the speed limit than cars. Similar results are described for scooters. Also examined are the influences on mean speeds such as the time of day, the presence of a car at the t-intersection, and the influence of free headway. The results are compared for robustness across locations and days. It is concluded that in urban areas motorcycles are travelling significantly faster than other traffic. These findings are discussed against a concern to reduce motorcycle crashes by improving conspicuity and previous research that implicates a ‘looked-but-failed-to-see’ effect for car drivers.     

Impact of speed change on estimated journey time: Failure of drivers to appreciate relevance of initial speed

Higher speeds are associated with increases in the probability of crashing and the severity of the outcome. Logically drivers speed to save time, and research evidence supports this assertion. It is therefore important to investigate drivers’ understanding of how speed change impacts on journey time. Since it is likely that drivers do not appreciate the reciprocal nature of the function which links these two variables, and its implications, two predictions can be made: the impact of a speed change will be underestimated at low speeds and overestimated at high speeds. This issue was addressed through four questions generated by manipulating Speed Change (increase versus decrease) and Starting Speed (30 mph versus 60 mph) with the participants being asked how they felt these variables would impact on journey time. These were included in a large survey addressing speed-related issues. Participants were a representative quota sample of 1005 UK drivers, interviewed by questionnaire. The findings indicated that three of the four questions produced results consistent with the predictions made. Furthermore, a repeated measures factorial ANOVA indicated that there was no real appreciation of how starting speed impacted on journey time. A disordinal interaction provided evidence that drivers wrongly believed that as starting speed increased the impact of a speed rise also increased; the opposite is true. For speed decreases, drivers appeared to think that starting speed had little impact on the amount of time saved. It is recommended that these findings be integrated into driver training and speed awareness courses.     

Illegal road crossing behavior of pedestrians at overpass locations: Factors affecting gap acceptance,crossing times and overpass use

The aim of designing overpasses is to provide safe road crossings for pedestrians by helping them to avoid conflicts with motor vehicles. However, the number of pedestrians who do not use overpasses to cross the road is very high. An observational survey of illegal road crossings was conducted at four overpass locations in Izmir, Turkey to determine the crossing time, crossing speed of the pedestrians and their distance and time gap perception for safe road-crossing within 25 m of the overpasses in both directions. Crossing time is the time needed for a pedestrian to cross a particular road. Time gap is strongly related with safety margin. If a pedestrian chooses a larger time gap, then the arrival time of the oncoming vehicle to the crossing point of the pedestrian increases thus, the possibility of a collision decreases. Each overpass was observed on weekdays during peak afternoon (12.30–13.30) and evening hours (17.00–18.00). At all overpass locations 454 illegal crossings were observed. ANOVA results revealed that age had a significant effect both on safety margin and crossing time. During the observations a survey was conducted among pedestrians who completed their crossings either using the overpass or at street level within 25 m of the overpass (n = 231). Factors affecting the crossing choice of pedestrians were specified in the surveys. The major part of the respondents (71.7%) indicated that time saving was the main reason for crossing at street level. Pedestrians’ crossing speeds were extracted from the video recordings to observe the effect of speed limit on pedestrian behavior. As a result, at locations where the speed limit was 70 km/h, pedestrians’ average crossing speed was found to be 1.60 m/s and 1.73 m/s while at locations where the speed limit was 50 km/h, pedestrians’ average crossing speed was found to be 1.04 m/s and 0.97 m/s. This shows that pedestrians feel safer while crossing when the vehicle speed is low.     

Predicting motorcyclists’ intentions to speed: Effects of selected cognitions from the theory of planned behaviour, self-identity and social identity

This study sought to identify cognitive predictors of motorcyclists’ intentions to speed using a model that comprised selected constructs from the theory of planned behaviour (TPB), supplemented with constructs from identity theory and social identity theory. Participants (N = 110) were sampled from motorcycle clubs in Scotland and they completed web-based questionnaire measures of all cognitive variables, operationalized with respect to speeding on both 30 mph urban roads and 70 mph dual carriageways and motorways. In support of the TPB element of the model, affective attitude and perceived controllability accounted for significant variance in intention to speed on each road type. The identity constructs accounted for additional variance in intentions to speed on 70 mph roads. The significant independent predictors of speeding intentions on 30 mph roads were affective attitude and perceived controllability. For 70 mph roads, the independent predictors of intention were affective attitude, self-identity, perceived group norm, group identification, and an interaction between perceived group norm and group identification. Consistent with predictions derived from social identity theory, decomposition of the interaction showed that perceived group norm had an increasing effect on intention with increases in group identification. Implications for theory development and safety interventions are discussed.     

Crash and burn? Vehicle,collision, and driver factors that influence motor vehicle collision fires

A retrospective population-based case–control study was performed to determine the association between vehicle fires, and vehicle, collision, and driver factors on highways with a posted speed limit of at least 55 mph. Data were obtained from the Kentucky Collision Report Analysis for Safer Highways (CRASH) electronic files for 2000–2009 from the Kentucky State Police Records Sections. The results from the final multiple logistic regression show that large trucks were at a higher risk for a collision involving a fire than passenger vehicles and pickup trucks. When controlling for all other variables in the model, vehicles 6 years old and older, driving straight down the highway, and single vehicle collisions were also identified as factors that increase the risk of motor vehicle collision fires on roadways with a posted speed limit of ≥55 mph. Of the 2096 vehicles that caught fire, there were 632 (30%) non-fatally injured drivers and 224 (11%) fatally injured drivers. The results of this study have the potential to inform public health messages directed to the transportation industry, particularly semi truck drivers, in regard to fire risk.     

Influence of road markings,lane widths and driver behaviour on proximity and speed of vehicles overtaking cyclists

The proximity and speed of motor traffic passing cyclists in non-separated conditions may be so close and so great as to cause discomfort. A variety of road design and driver behaviour factors may affect overtaking speeds and distances. The investigation presented in this paper builds on previous research and fills gaps in that research by considering the presence of cycle lanes on 20 mph and 30 mph roads, different lane widths, different lane markings, vehicle type, vehicle platooning and oncoming traffic. Data were collected from a bicycle ridden a distance of one metre from the kerb fitted with an ultrasonic distance detector and forward and sideways facing cameras.     

How to present collision warnings at intersections?—A comparison of different approaches

Analyses of intersection accidents have shown that in most cases drivers overlook or see other road users with the right of way too late that they cannot react in time. Appropriate visual warning signals which support drivers in their attention allocation and driving behavior could be useful to improve drivers’ reaction. In a driving simulator study, two warning strategies varying in their timing: (1) top-down warning while approaching a critical intersection and (2) bottom-up warning directly before the critical incident were investigated in a T-intersection situation. For the bottom-up warning, two warning signal designs were compared. 48 subjects (M = 27.3 years, SD = 7.4 years) participated in the study. Driving data as well as subjective evaluation of the three warning signals (one early and two late warning signals) were analyzed. The early warning signal which was given while approaching the intersection showed a positive effect. Here, most collisions could be avoided due to drivers’ adaptation of their driving behavior toward safer driving. They waited longer at the intersection before turning and finally turned with a lower velocity. In addition, drivers evaluated the early warning signal as very “useful”. With regard to the late warnings a much smaller effect was found. From these results, requirements can be derived for the design of effective warning strategies when driving at critical intersections.     

Evaluation of the Scottsdale Loop 101 automated speed enforcement demonstration program

Speeding is recognized as a major contributing factor in traffic crashes. In order to reduce speed-related crashes, the city of Scottsdale, Arizona implemented the first fixed-camera photo speed enforcement program (SEP) on a limited access freeway in the US. The 9-month demonstration program spanning from January 2006 to October 2006 was implemented on a 6.5 mile urban freeway segment of Arizona State Route 101 running through Scottsdale. This paper presents the results of a comprehensive analysis of the impact of the SEP on speeding behavior, crashes, and the economic impact of crashes. The impact on speeding behavior was estimated using generalized least square estimation, in which the observed speeds and the speeding frequencies during the program period were compared to those during other periods. The impact of the SEP on crashes was estimated using 3 evaluation methods: a before-and-after (BA) analysis using a comparison group, a BA analysis with traffic flow correction, and an empirical Bayes BA analysis with time-variant safety. The analysis results reveal that speeding detection frequencies (speeds ≥ 76 mph) increased by a factor of 10.5 after the SEP was (temporarily) terminated. Average speeds in the enforcement zone were reduced by about 9 mph when the SEP was implemented, after accounting for the influence of traffic flow. All crash types were reduced except rear-end crashes, although the estimated magnitude of impact varies across estimation methods (and their corresponding assumptions). When considering Arizona-specific crash related injury costs, the SEP is estimated to yield about $17 million in annual safety benefits.     

Mind the gap: training road users to use speed and distance when making gap-acceptance decisions

Accurate gap-acceptance decisions require individuals to take into account both the distance to and the speed of an oncoming vehicle. The aim of the present studies was to develop an intervention that could successfully teach road users to focus on speed as well as distance. Across three studies, participants judged whether it was safe to cross the road or not when an oncoming vehicle was approaching from different distances and at different speeds. Study 1 trialed two techniques (“standard feedback” versus “three-look”) aimed at improving gap judgments. Standard feedback involved telling participants what the actual speed of a car was after they had made an estimate, whereas the three-look technique required participants to make timed and controlled head movements when scanning the road environment. Only standard feedback increased the participants’ mean gap-acceptance accuracy (assessed using both verbal and behavioral response measures). Study 2 also trialed two techniques, the standard feedback intervention used in Study 1, and a “two-response” intervention in which participants judged whether the oncoming vehicle was traveling at an atypical or normal speed. Study 2 found the two-response intervention to be more promising than the standard feedback procedure. Finally, Study 3 used video footage of oncoming vehicles to train younger (18–27 years) and older (60–80 years) adults and found the two-response intervention to be successful at improving gap-acceptance accuracies for both age groups. However, the intervention also resulted in more conservative gap judgments from participants in the older population independent of improvements in accuracy.     

What does the driver look at? The influence of intersection characteristics on attention allocation and driving behavior

One of the main contributing factors with intersection accidents is lack of information due to attention allocation. In many cases, drivers fail to yield right of way to other traffic participants. One reason is that drivers have inappropriate expectations about a traffic situation. They allocate their attention primarily to certain areas of the intersection but neglect others. In a driving simulator study, the influence of intersection complexity on drivers’ expectations and their driving behavior was examined. In two T-intersections, the complexity was varied by the traffic density (low and high) using either one or two important objects: vehicles (left) with or without pedestrians (right). Additionally, the reaction to two critical incidents in close proximity of the intersections was examined. Gaze behavior, vehicle reactions, and subjective data were recorded. 40 subjects (26 male, 14 female, M = 31.0 years, SD = 11.9 years) participated in the study. Interestingly, the least complex intersections showed the most accidents which was interpreted as the result of inadequate attention allocation. It was shown that both the drivers’ attention allocation and vehicle velocity when turning off were responsible for this effect. The results contribute to a better understanding of the role of drivers’ expectation and attention allocation in the causation of intersection accidents.     

Aggregate nonparametric safety analysis of traffic zones

Exploring the significant variables related to specific types of crashes is vitally important in the planning stage of a transportation network. This paper aims to identify and examine important variables associated with total crashes and severe crashes per traffic analysis zone (TAZ) in four counties of the state of Florida by applying nonparametric statistical techniques such as data mining and random forest. The intention of investigating these factors in such aggregate level analysis is to incorporate proactive safety measures in transportation planning. Total and severe crashes per TAZ were modeled to provide predictive decision trees. The variables which carried higher weight of importance for total crashes per TAZ were – total number of intersections per TAZ, airport trip productions, light truck productions, and total roadway segment length with 35 mph posted speed limit. The other significant variables identified for total crashes were total roadway length with 15 mph posted speed limit, total roadway length with 65 mph posted speed limit, and non-home based work productions. For severe crashes, total number of intersections per TAZ, light truck productions, total roadway length with 35 mph posted speed limit, and total roadway length with 65 mph posted speed limit were among the significant variables. These variables were further verified and supported by the random forest results.     

Hours of service violations among tractor-trailer drivers

Federal regulation limits interstate truck drivers to 10 hours of driving after an 8-hour off-duty period. The need for enforcing these limits is supported by research showing that long driving hours is a risk factor for tractor-trailer crashes. To estimate the percentage of hours of service violators among long-haul tractor-trailer drivers, truck drivers were interviewed at an inspection site in Spokane, Washington and later observed arriving at inspection sites in either Moorhead or Worthington, Minnesota (approximately 1,200 miles). The sample used for the calculation of violators consisted of truckers driving alone who reportedly did not plan to make an interim pickup or delivery stop prior to arrival in Minnesota. The percentages of drivers violating the hours of service rules by more than one hour at average trip speeds ranging from 35 mph to 65 mph are presented. Assuming that the drivers averaged 40 mph over the complete course of the trip segment, including stopped time, 90% were in violation by more than one hour. Assuming that they averaged 50 mph, 51% were in violation by more than one hour. These speed assumptions are based on findings in the current study that team drivers averaged 38 mph, fleet managers' reports of scheduling single drivers at trip speeds of 45 mph to 47 mph, and reports in the literature that loaded tractor-trailers average 41 mph over flat terrain. Although the true percentage cannot be determined without knowing actual trip speeds, the estimated range of violators at probable speeds of 40 mph and 50 mph points to a substantial problem.     

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.     

Rear seat safety: Variation in protection by occupant,crash and vehicle characteristics

Objectives

Current information on the safety of rear row occupants of all ages is needed to inform further advances in rear seat restraint system design and testing. The objectives of this study were to describe characteristics of occupants in the front and rear rows of model year 2000 and newer vehicles involved in crashes and determine the risk of serious injury for restrained crash-involved rear row occupants and the relative risk of fatal injury for restrained rear row vs. front passenger seat occupants by age group, impact direction, and vehicle model year.

Method

Data from the National Automotive Sampling System Crashworthiness Data System (NASS-CDS) and Fatality Analysis Reporting System (FARS) were queried for all crashes during 2007–2012 involving model year 2000 and newer passenger vehicles. Data from NASS-CDS were used to describe characteristics of occupants in the front and rear rows and to determine the risk of serious injury (AIS 3+) for restrained rear row occupants by occupant age, vehicle model year, and impact direction. Using a combined data set containing data on fatalities from FARS and estimates of the total population of occupants in crashes from NASS-CDS, logistic regression modeling was used to compute the relative risk (RR) of death for restrained occupants in the rear vs. front passenger seat by occupant age, impact direction, and vehicle model year.

Results

Among all vehicle occupants in tow-away crashes during 2007–2012, 12.3% were in the rear row where the overall risk of serious injury was 1.3%. Among restrained rear row occupants, the risk of serious injury varied by occupant age, with older adults at the highest risk of serious injury (2.9%); by impact direction, with rollover crashes associated with the highest risk (1.5%); and by vehicle model year, with model year 2007 and newer vehicles having the lowest risk of serious injury (0.3%). Relative risk of death was lower for restrained children up to age 8 in the rear compared with passengers in the right front seat (RR = 0.27, 95% CI 0.12–0.58 for 0–3 years, RR = 0.55, 95% CI 0.30–0.98 for 4–8 years) but was higher for restrained 9–12-year-old children (RR = 1.83, 95% CI 1.18–2.84). There was no evidence for a difference in risk of death in the rear vs. front seat for occupants ages 13-54, but there was some evidence for an increased relative risk of death for adults age 55 and older in the rear vs. passengers in the right front seat (RR = 1.41, 95% CI 0.94–2.13), though we could not exclude the possibility of no difference. After controlling for occupant age and gender, the relative risk of death for restrained rear row occupants was significantly higher than that of front seat occupants in model year 2007 and newer vehicles and significantly higher in rear and right side impact crashes.

Conclusions

Results of this study extend prior research on the relative safety of the rear seat compared with the front by examining a more contemporary fleet of vehicles. The rear row is primarily occupied by children and adolescents, but the variable relative risk of death in the rear compared with the front seat for occupants of different age groups highlights the challenges in providing optimal protection to a wide range of rear seat occupants. Findings of an elevated risk of death for rear row occupants, as compared with front row passengers, in the newest model year vehicles provides further evidence that rear seat safety is not keeping pace with advances in the front seat.     

Dynamic strength evaluations for self-piercing rivets and resistance spot welds joining similar and dissimilar metals

This paper summarizes the dynamic joint strength evaluation procedures and the measured dynamic strength data for 13 joint populations of self-piercing rivets (SPR) and resistance spot welds (RSWs) joining similar and dissimilar metals. A state-of-the-art review of the current practice for conducting dynamic tensile/compressive strength tests in different strain rate regimes is first presented, and the generic issues associated with dynamic strength test are addressed. Then, the joint strength testing procedures and fixture designs used in the current study are described, and the typical load versus displacement curves under different loading configurations are presented. Uniqueness of the current data compared with data in the open literature is discussed. The majority of experimental results indicate that joint strength increases with increasing loading rate. However, the strength increase from 4.47 m/s (10 mph) to 8.94 m/s (20 mph) is not as significant as the strength increase from static to 4.47 m/s. It is also found that with increasing loading velocity, displacement to failure decreases for all the joint samples. Therefore, ‘brittleness’ of the joint sample increases with impact velocity. Detailed static and dynamic strength data and the associated energy absorption levels for all the samples in the 13 joint populations are also included.     

Controlling the oriented growth of Ti2SnC grains with carbon fiber as a reactive template in the Ti-Sn-C system

Carbon short fibers with a length of ∼3 mm used as a reactive template were mixed with Ti and Sn powders. The mixture was pressurelessly sintered at 1200 °C for 2 h in a vacuum atmosphere. The microstructure shows that Ti₂SnC grains with a plate-like shape grow along a preferred direction, forming a ‘string’ structure in which Ti₂SnC platelets pack themselves closely with a top-bottom-top-bottom sequence. With increasing the length of the C fibers, the length of the ‘string’ structures increases. A large amount of long and aligned ‘string’ structures have formed after sintering the samples prepared by infiltration of the carbon short fibers with a length of ∼50 mm in a Ti-Sn slurry and then stacking and cold pressing. X-ray diffraction and scanning electron microscopy, respectively were used to analyze and observe the phase composition and microstructure.     

Analysis of developed transition road safety barrier systems

Road safety barriers protect vehicles from roadside hazards by redirecting errant vehicles in a safe manner as well as providing high levels of safety during and after impact. This paper focused on transition safety barrier systems which were located at the point of attachment between a bridge and roadside barriers. The aim of this study was to provide an overview of the behavior of transition systems located at upstream bridge rail with different designs and performance levels. Design factors such as occupant risk and vehicle trajectory for different systems were collected and compared. To achieve this aim a comprehensive database was developed using previous studies. The comparison showed that Test 3–21, which is conducted by impacting a pickup truck with speed of 100 km/h and angle of 25° to transition system, was the most severe test. Occupant impact velocity and ridedown acceleration for heavy vehicles were lower than the amounts for passenger cars and pickup trucks, and in most cases higher occupant lateral impact ridedown acceleration was observed on vehicles subjected to higher levels of damage. The best transition system was selected to give optimum performance which reduced occupant risk factors using the similar crashes in accordance with Test 3–21.     

Effect of joint mechanism on vehicle redirectional capability of water-filled road safety barrier systems

Portable water-filled barriers (PWFBs) are roadside appurtenances that prevent vehicles from penetrating into temporary construction zones on roadways. PWFBs are required to satisfy the strict regulations for vehicle re-direction in tests. However, many of the current PWFBs fail to re-direct the vehicle at high speeds due to the inability of the joints to provide appropriate stiffness. The joint mechanism hence plays a crucial role in the performance of a PWFB system at high speed impacts. This paper investigates the desired features of the joint mechanism in a PWFB system that can re-direct vehicles at high speeds, while limiting the lateral displacement to acceptable limits. A rectangular “wall” representative of a 30 m long barrier system was modeled and a novel method of joining adjacent road barriers was introduced through appropriate pin-joint connections. The impact response of the barrier “wall” and the vehicle was obtained and the results show that a rotational stiffness of 3000 kNm/rad at the joints seems to provide the desired features of the PWFB system to re-direct impacting vehicles and restrict the lateral deflection. These research findings will be useful to safety engineers and road barrier designers in developing a new generation of PWFBs for increased road safety.