Investigating the impact of a novel active gap metering signalization strategy on driver behavior at highway merging sections

A safe headway to the lead vehicle is important to reduce conflicts with merging vehicles from highway on-ramps. Previous research has outlined the advantage of gap metering strategies to yield sufficient space to merging vehicles and improve highway capacity during peak hours. However, prevailing gap metering systems fail to indicate the minimum required gap and leave it to the drivers’ judgment to adjust their headway. This paper proposes a new Active Gap Metering (AGM) signalization that helps outer lane drivers to adjust their headway to the lead vehicle when approaching highway ramps with incoming vehicles. This AGM signalization represents a combination of pavement markings and an innovative Variable Message Sign (VMS). The AGM system was tested alone and in combination with additional variable speed limits (VSL) in distinct environments of the Doha Expressway in the State of Qatar using a driving simulator. The driving behavior of 64 drivers was analyzed using repeated-measures ANOVA. The results showed that the AGM effectively influenced the drivers’ behavior on the right stream lane. Drivers did gradually increase the distance to the lead vehicle, which resulted in optimal headways to merging on-ramp vehicles. Most importantly, the minimum time-to-collision (TTC_min) to the merging vehicle was increased by an additional 1–1.5 s as compared to no treatment. The proposed AGM signalization can, therefore, be considered by policymakers to influence drivers’ headways at critical merging sections.     

Effects of variable message signs for slippery road conditions on reported driver behaviour

A field study by Rämä and Kulmala (Rämä, P., Kulmala, R. (2000). Effects of variable message signs for slippery road conditions on driving speed and headways. Transportation Research, Part F, 3, 85–94.) showed that a variable message sign warning about slippery road conditions reduced the mean speed by 1–2 km/h. The study also showed that a variable message sign recommending a minimum headway between vehicles decreased the proportion of short headways. However, the signs may have other effects on driver behaviour besides those measurable in terms of speed and headway, and this study was designed to investigate such potential effects. In total, 114 drivers who had encountered the slippery road condition sign and 111 drivers who had encountered the sign showing recommended minimum headway in adverse road surface conditions were interviewed. The results suggested that these variable message signs do indeed have other effects, such as the refocusing of attention to seek cues on potential hazards, testing the slipperiness of the road, and more careful passing behaviour. On the other hand, the results suggested that driving speed and headway are essential variables with which many other variables correlate.     

A systematic review of definitions of motor vehicle headways in driver behaviour and performance studies

Headway is a safety measure commonly used to investigate driving behaviour and driver performance. Its purpose is to reflect the following distance or time between a leading and following vehicle in traffic. It is therefore associated with drivers’ response time, such as in braking or swerving, during safety critical events. In the literature, distance and time headway are defined in different ways, despite standard definitions in the traffic engineering literature, which prompted this systematic review of headway definitions across a range of study designs, in order to recommend approaches to improve the accuracy and reproducibility of headway definitions used in road safety contexts. PRISMA guidelines were followed to search four databases (EMBASE, COMPENDEX, SCOPUS and MEDLINE) for studies that reported on headways or discussed methodological approaches. The search and filtering of abstracts identified 110 articles for a qualitative synthesis. Four broad approaches to measuring headways were detected: studies using simulation, roadside external features, on-road features, and on-vehicle features. Studies were coded as to whether they included written explanation, mathematical statements, or pictorial depictions of headway. Only 49.6% of studies contextualised headway sufficiently for reproducibility. Reproducibility is crucial for accurate interpretation of research findings and comparisons across studies. It is recommended that headway definitions should a) exclude vehicle or parts of vehicle lengths, b) include reference points (e.g., bumper/axle/rear), c) have a consistent terminology, and d) include the accuracy of headway measuring devices to report the precision of a study’s findings.     

Imperfect in-vehicle collision avoidance warning systems can aid distracted drivers

The purpose of this study was to evaluate the efficacy of a type of in-vehicle collision avoidance warning system (IVCAWS) under conditions of driver distraction. Forty-three participants responded to an imperfect warning system while simultaneously driving a simulator and performing a visual/cognitive task. The major concerns were whether drivers would be more inclined to rely on such a system when they are distracted by subsidiary tasks, and if this reliance would be counterproductive. We found that distracted drivers responded, by increasing their temporal headway, to the less reliable system’s alarms, but the warning system at the higher reliability levels led to over reliance and ultimately to maintaining shorter headways. This study has practical implications for the use of warning systems as driving aids for drivers. Although aids may be helpful and, in many cases, the more reliable aid is preferable, in the case of distraction, drivers may misuse the aid.     

Naturalistic observation of drivers’ hands, speed and headway

Drivers’ hands position have been shown to vary with traffic speed and complexity of the driving environment, such that drivers are more likely to place two hands on the top half of the steering wheel as the supposed driving difficulty increases (Walton, D. & Thomas, J. A. [2005]. Naturalistic observations of driver hand positions. Transportation Research Part F, 8, 229–238). This research evaluates drivers’ hands positions, examining the reliability of the measure and the relationship between the positions of the driver’s hands, vehicle speed, vehicle headway and driver sex. The findings show that the observed positions of drivers’ hands have good inter-rater reliability and demonstrate both temporal and contextual reliability. The positions of drivers’ hands are related to other measures, such that drivers with lower-ranked positions of hands are more likely to travel at higher speeds and accept shorter headways. Female drivers are found to be 2.87 times more likely than males to place two hands rather than one hand on the top half of the steering wheel.     

What characterizes a “free vehicle” in an urban area?

The concept “free vehicle” is used widely in the transportation research literature, but as yet there is no common standard for a definition. In this article a standard is provided that is based on the assumption that a vehicle can be considered free, when its speed is not influenced by the speed of the vehicle traveling ahead. In order to determine empirically a threshold for free vehicles in urban areas, speed, distance headway, and time headway data of more than 100 000 vehicles were analyzed. Analyses showed that the speeds of two vehicles are linearly dependent on time headway for headways up to 6 s. It is important to distinguish between this value and the drivers' preferred headway, which is in the region of 2 s.     

Adaptations in driver deceleration behaviour with automatic incident detection: A naturalistic driving study

Traffic congestion and crash rates can be reduced by introducing variable speed limits (VSLs) and automatic incident detection (AID) systems. Previous findings based on loop detector measurements have revealed that drivers reduce their speeds while approaching traffic congestion when the AID system is active. Notwithstanding these behavioural effects, most microscopic traffic flow models assessing the impact of VSLs do not describe driver response accurately.This study analyses the main factors that influence driver deceleration behaviour while approaching traffic congestion with and without VSLs. The Dutch VSL database was linked to the driver behaviour data collected in the UDRIVE naturalistic driving study. Driver engagement in secondary tasks and glance behaviour were extracted from the video data. Linear mixed-effects models predicting the characteristics of deceleration events were estimated.The results show that the maximum deceleration is high when approaching a slower leader, when driving at high speeds and short distance headways, and close to the beginning of traffic congestion. The minimum time headway is short when driving at high speeds and changing lanes. Certain drivers showed higher decelerations and shorter time headways than others. Controlled for these main factors, smaller maximum decelerations were found when the VSLs were present and visible, and when the gantries were within close proximity. These factors could be incorporated into microscopic traffic simulations to evaluate the impact of AID systems on traffic congestion more realistically. Further research is needed to clarify the link between engagement in secondary tasks, glance behaviour and deceleration behaviour.     

Intraindividual variability in driving simulator parameters of healthy drivers of different ages

Intraindividual variability is a fundamental behavioural characteristic of aging but has been examined to a very limited extent in driving. This study investigated intraindividual variability in driving simulator measures in healthy drivers of different ages using the coefficient of variation (COV) as a variability measure. Participants were healthy volunteers who were regular drivers, who were divided into a “young” group, a “middle-aged” group, and an “old” group. They drove in two environments (rural, 72 drivers; urban, 60 drivers), under conditions of moderate and high traffic load, without and with distraction (conversation). Significant differences in COV were observed in the rural condition for headway distance and lateral position as a function of traffic load, with high traffic (without and with distraction) resulting in increased COV of headway and decreased COV of lateral position. Significant differences in COV were observed in the urban condition for headway distance only, with high traffic (without and with distraction) resulting in increased COV of headway. No age effects were found for any of the driving conditions. The results indicate that traffic load affected headway distance and lateral position in opposite directions in all three age groups: high traffic resulted in increased variability of headway in both rural and urban conditions but in decreased variability of lateral position in the rural conditions compared to moderate traffic irrespective of distraction. The study indicates that driving conditions affect the intraindividual variability of driving measures in selective ways, which may be linked to the extent of automatization of the driving variables and to adaptive changes to traffic condition challenges.     

Headway on urban streets: observational data and an intervention to decrease tailgating

A method to collect headway (tailgating) data in an urban setting was implemented and produced reliable headway data on over 25 000 drivers. Data are reported on the effectiveness of two hand-held roadside signs admonishing drivers not to tailgate. One of these signs (that included a reference to “crashes”) had a significantly positive impact on drivers' headway. Drivers’ followed with an average headway of 2.11 s when the sign was absent compared to an average headway of 2.29 s when the sign was present. When the sign was absent, 49.4% of the drivers were in compliance with the 2-second rule compared to 57.5% when the sign was present. The percentage of drivers who followed with a headway of less than 1 s decreased from 7.3 when the sign was absent to 3.0 when the sign was present. Additionally, there was an increase of 10.6 ft in vehicle separation from baseline to intervention.     

Increasing following headway with prompts, goal setting, and feedback in a driving simulator

We evaluated the effects of prompting, goal setting, and feedback on following headway of young drivers in a simulated driving environment and assessed whether changes produced in following headway were associated with reductions in hard braking when drivers were and were not using cell phones. Participants were 4 university students. During baseline, drivers spent half of the time talking on cell phones while driving. At the start of the intervention, drivers were prompted to increase following headway while on the cell phones and were provided a specific target for following headway. Drivers were given feedback on increasing following headway when on cell phones at the end of each session. The intervention package was associated with an increase in following headway and a decrease in hard braking when participants were on and off the cell phones. Cell phone use did not affect any of the measures.     

Effects of variable message signs for slippery road conditions on driving speed and headways

This field study investigated the effects of two variable message signs (VMS) on driver behaviour. Specifically, the signs were a warning sign for slippery road conditions and a minimum headway sign. The study was performed as a before-and-after experiment at three test sites in Finland with an after period covering two winter seasons. The results showed that the slippery road condition sign reduced the mean speed on slippery roads by 1–2 km/h in addition to the decrease caused by the adverse road conditions. The minimum headway sign decreased the proportion of headways shorter than 1.5 s for cars in car-following situations, in addition to a speed reduction of 1 km/h. The effects were somewhat smaller during the second winter than the first.     

Comparative assessment of the behaviour of drivers with Mild Cognitive Impairment or Alzheimer’s disease in different road and traffic conditions

The objective of this research was the analysis of the driving performance of drivers with Mild Cognitive Impairment (MCI) or Alzheimer’s disease (AD), in different road and traffic conditions, on the basis of a driving simulator experiment. In this experiment, healthy “control” drivers, patients with MCI, and patients with AD, drove at several scenarios at the simulator, after a thorough neurological and neuropsychological assessment. The scenarios include driving in rural and urban areas in low and high traffic volumes. The driving performance of healthy and impaired drivers was analysed and compared by means of Repeated Measures General Linear Modelling techniques. A sample of 75 participants was analysed, out of which 23 were MCI patients and 14 were AD patients. Various driving performance measures were examined, including longitudinal and lateral control measures. The results suggest that the two examined cerebral diseases do affect driving performance, and there were common driving patterns for both cerebral diseases, as well as particular characteristics of specific pathologies. More specifically, cognitively impaired drivers drive at lower speeds and with larger headway compared to healthy drivers. Moreover, they appear to have difficulties in positioning the vehicle on the lane. The group of patients had difficulties in all road and traffic environments, and especially when traffic volume was high. Most importantly, both cerebral diseases appear to significantly impair reaction times at incidents. The results of this research suggest that compensatory behaviours developed by impaired drivers are not adequate to counterbalance the direct effects of these cerebral diseases on driving skills. They also demonstrate that driving impairments increase as cognitive impairments become more severe (from MCI to AD).     

Determinants of following headway in congested traffic

This paper reports on results of a study undertaken in the UK aimed at investigating factors affecting the car following process. An understanding of the factors affecting this complex decision making process is essential to a wide range of theoretical issues including driver workload, capacity and the modeling of freeway flow, as well as practical applications such as the design of in-vehicle driver aids and assistance systems, many of which have direct relevance to increasing driver safety. The study used an instrumented vehicle to collect time dependent following data for a group of test drivers. Data was collected on two differing types of high speed road, using six primary subjects who drove a test vehicle, supplemented by data on 123 drivers that were observed following the test vehicle. Examination was made of how the time headway chosen by a driver is influenced by a range of situational variables commonly believed to effect behavior, with four main findings. Firstly, headway was found to change according to the type of vehicle being followed (i.e. subjects followed closer to trucks than to cars), secondly, little variation was found with changes in overall traffic flow, thirdly, little correlation was found with road type, and lastly a distinct day-to-day variation in individual behavior was observed.     

Safety of bicyclists in roundabouts with mixed traffic: Video analyses of behavioural and surrogate safety indicators

Although converting an intersection into a roundabout has been shown to result in fewer injury accidents for both motor vehicle drivers and pedestrians, the effect on bicyclists’ safety is unclear or even negative. This study focuses on roundabouts without bicycle facilities (i.e., mixed traffic conditions) and makes use of semi-automated video observation software with the aim of analysing bicyclists’ behaviour and safety on roundabouts with different diameter. Four urban roundabouts in Belgium are observed. Interactions between bicyclists and other vehicles are analysed using speed, lateral position and five indicators to describe the closeness of interactions (TTC_min, PET, T_{2 min}, lateral overtaking proximity and minimum distance headway). Additionally, the lateral position and riding speed of bicyclists that are in interaction with other vehicles is compared with the behaviour of bicyclists that are not in interaction with other vehicles.The behavioural analysis revealed that regardless of the type of condition (free-flow bicyclists or different interactions bicyclist-car), bicyclists always ride faster on roundabouts with big diameter and slower on roundabouts with small diameter. Moreover, bicyclists ride closer to the central island on roundabouts with big diameter compared to roundabouts with small diameter for all the conditions analysed.The analysis of surrogate safety indicators (TTC_min, PET, T_{2 min}) revealed that close interactions between bicyclists and cars are relatively frequent at both small and big roundabouts. The percentages of close interactions are more or less equal for roundabouts with big diameter (7.86% of observed interactions) and roundabouts with small diameter (8.24%). The analysis of the indicators to describe the closeness of interactions also showed that the closest interactions at roundabouts are all situations where the bicyclist has a leading role. The analysis of the most common types of close interactions revealed indeed that the most common close interactions are interactions where the bicyclist is entering the roundabout. The analysis of lateral overtaking proximity showed that bicyclists who overtake a car take smaller lateral overtaking proximities compared to cars overtaking a bicyclist. The analysis of minimum distance headway finally revealed that bicyclists who ride behind a car take smaller distance headways compared to cars driving behind a bicyclist.     

Safety at first sight? – Manual drivers’ experience and driving behavior at first contact with Level 3 vehicles in mixed traffic on the highway

Soon, manual drivers will interact with conditionally automated vehicles (CAVs; SAE Level 3) in a mixed traffic on highways. As of yet, it is largely unclear how manual drivers will perceive and react to this new type of vehicle. In a driving simulator study with N = 51 participants aged 20 to 71 years (22 female), we examined the experience and driving behavior of manual drivers at first contact with Level 3 vehicles in four realistic driving scenarios (highway entry, overtaking, merging, introduction of a speed limit) that Level 3 vehicles may handle alone once their operational domain extends beyond driving in congested traffic. We also investigated the effect of an external marking via a visual external human–machine interface (eHMI), with participants being randomly assigned to one of three experimental groups (none, correct, incorrect marking). Participants experienced each driving scenario four times, twice with a human-driven vehicle (HDV), and twice with a CAV. After each interaction, participants rated perceived driving mode of the target vehicle as well as perceived safety and comfort. Minimum time headways between participants and target vehicles served as an indicator of safety criticality in the interactions. Results showed manual driver can distinguish CAVs from HDVs based on behavioral differences. In all driving scenarios, participants rated interactions with CAVs at least as safe as interactions with HDVs. The driving data analysis showed that manual driver interactions with CAVs were largely uncritical. However, the CAVs’ strict rule-compliance led to short time headways of following manual drivers in some cases. The eHMI used in this study neither affected the subjective ratings of the manual drivers nor their driving behavior in mixed traffic. Thus, the results do not support the use of eHMIs on the highway, at least not for the eHMI design used in this study.     

Personality and demographic differences in the perceived risks of potentially timid driving behaviours

Timid driving behaviours can be described as overly cautious and hesitant driving behaviours. Little research has examined behaviours that potentially resemble timid driving and how these behaviours are perceived by other drivers. This is despite the potential for these behaviours to be perceived in a way that leads to angry and aggressive retaliatory behaviours in some drivers (e.g., in anger-prone drivers). We conducted an online survey examining the perceived road safety risks of several behaviours that could potentially result from timid driving and their relationships with driver personality (trait anxiety, trait driving anger), behaviour (anxious driving, angry driving), and demographic (age, gender, annual mileage) background. Drivers (N = 439, M_age = 49.41 ± 5.59 years, aged 18–89) perceived excessively cautious and unpredictable braking behaviours as posing moderate levels of risk. Multiple linear regression analyses also indicated higher perceived risks of slow and excessively cautious behaviours in older, male, and anger prone drivers. No meaningful associations were found between driver characteristics and the risks of unpredictable braking behaviours. These results suggest that safety campaigns to reduce aggressive behaviour may benefit from targeting the perceptions of other drivers’ behaviours.     

Socio-economic and driving experience factors affecting drivers’ perceptions of traffic crash risk

Drivers are estimated to contribute an overwhelming proportion to the burden of traffic crashes, as factors that increase crash risk are frequently due to unsafe driving behaviours. The relationship between risk perceptions and people’s risky driving behaviours is still not well understood. This paper aims to further analyse the potential effect of risky driving behaviours on drivers’ perceptions of crash risk and differences in perceptions among drivers.Crash risk perceptions in an inter-city, two-way road context of 492 drivers were measured by using a Stated Preference (SP) ranking survey. Rank-ordered logit models were used to evaluate the impact on risk perception of five unsafe driving behaviours and to identify differences in drivers’ risk perceptions. The five unsafe driving behaviours considered in the analysis were respectively related to whether or not the driver follows the speed limits, the rules of passing another car and the safe distance, whether or not the driver is distracted, and whether or not she/he is driving under optimal personal conditions.All risky driving behaviours showed a significant potential effect (p < 0.001) on crash risk perceptions, and model’s results allowed to differentiate more important from less important unsafe driving behaviours based on their weight on perceived crash risk. Additionally, this paper further analyses the potential differences in risk perception of these traffic violations between drivers of different characteristics, such as driving experience, household size, income and gender.The SP technique could be applied to further analyse differences in perceptions of risky driving behaviours among drivers. Future research should consider the potential effect of driving skill on perceptions of risky driving behaviours.     

Effectiveness of the compensatory strategy adopted by older drivers: Difference between professional and non-professional drivers

It has been a controversial issue for the effect of ageing population on driving safety. Apparently, drivers’ physiological and cognitive performances deteriorate with age. However, older drivers may compensate for the elevated risk by adjusting their behaviors, known as compensatory strategy. Despite the extensive research on this topic, the compensatory strategy of older professional drivers is not well understood since many studies focused on the differences in compensatory behavior between older and young drivers. Professional drivers tend to be more skillful and able to cope with the unfavorable driving environments, thus presenting a higher capability to mitigate the risk. This study attempts to examine the compensatory behavior and its safety effect amongst older professional drivers, as compared to those of older non-professional drivers, using the driving simulator approach. In the driving simulator experiment, participants were asked to follow a leading vehicle for one hour, and two sudden brake events were presented. 41 (mid-aged and older) drivers completed the driving tests. Each participant was required to complete a car-following test, either under high or low traffic flow conditions. Performance indicators include driving capability (i.e. lateral control, longitudinal control, and brake reaction time) and compensatory behavior (i.e. average speed, and time headway). Additionally, two modified traffic conflict measures: time exposed time-to-collision (TET) and time integrated time-to-collision (TIT) are applied to indicate the traffic conflict risk. The random parameter Tobit models were estimated to measure the association between conflict risk and driver attributes, and random intercept models were used to assess other driving performance indicators. Results show that despite the impaired lateral control performance and longer brake reaction time of older drivers, the likelihood of severe traffic conflict of older drivers is lower than that of mid-aged drivers. Furthermore, though both older professional and older non-professional drivers adopted longer time headway, the reduction in the risk of severe traffic conflict is more profound among the older professional drivers. Such findings suggest that older professional drivers are more capable of mitigating the possible collision risk by adopting the compensatory strategy, as compared to older non-professional drivers. This justifies the existence of compound effect by the compensatory strategy of older driver and better driving skills of professional driver. This research provides useful insights into driver training and management strategies for employers, as older drivers would become a major cohort in the transportation industry.     

Self-regulatory driving behaviours amongst older drivers according to cognitive status

Self-regulation of older drivers was explored according to their cognitive status in this pilot study by examining situations commonly avoided by older drivers. In addition, the role of driver insight on self-regulation was examined via passenger reports. Telephone interviews were conducted comprising 49 drivers aged 65 years and above and 40 passengers who acted as informants. Self-regulation was found to be common, with the majority of drivers (71.4%) reporting sometimes or always avoiding one of seven driving situations. However, drivers with cognitive impairment reported self-regulating more often than drivers without cognitive impairment. The largest discrepancy between passenger and driver reports of self-regulation behaviours was found for the drivers with cognitive impairment. These results possibly reflect a decreased awareness of self-regulatory driving behaviours in this subgroup of older drivers and may suggest that other external factors are contributing to self-regulation in older drivers with cognitive impairment. A discussion of these factors is provided with the aim of maintaining mobility and enhancing quality of life in this growing segment of the driver population.     

Reducing behavioural risk factors for cancer: An affect regulation perspective

Nearly half of all cancer deaths are attributable to preventable causes, primarily unhealthy behaviours such as tobacco use, alcohol use and overeating. In this review, we argue that people engage in these behaviours, at least in part, as a means of regulating their affective states. To better understand why people engage in these behaviours and how researchers might design interventions to promote the selection of healthier methods for regulating affect, we propose a conceptual model of affect regulation. We synthesise research from both the stress and coping tradition as well as the emotion and emotion regulation tradition, two literatures that are not typically integrated. In so doing, we indicate where researchers have made headway in understanding these behaviours as affect regulation and note how our model could be used to structure future work in a way that would be particularly advantageous to cancer control efforts.