Driver responses to green and red vehicular signal countdown displays: Safety and efficiency aspects

An assessment of the effect of green signal countdown timers on drivers' behavior and on road safety at intersections, based on driving simulator experiments and naturalistic observation studies

INTRODUCTION

Motor-vehicle crashes at signalized intersections are a significant traffic safety problem. To address this problem, many Asian cities have installed signal countdown displays at signalized intersections, aiming to assist drivers to make correct decisions in response to traffic signals.

METHOD

In this study, we assessed the short-term and long-term effects of green signal countdown timers (GSCTs) on road safety, using a combination of driving simulator experiments and naturalistic observations.

RESULTS

In our driving simulator experiments, 80 participants drove at 50 km/h in scenarios in which a car either approached a signalized intersection alone or following another car. In naturalistic observations, short-term (1-week) and long-term (1-year) intersection safety in the presence and absence of GSCTs were compared. These observations revealed that GSCTs reduced the number of red-light-running violations over the short term, but not over the long term. In fact, GSCTs appeared to lead to an overall increase in rear-end crash risk at intersections, as their presence resulted in drivers exhibiting more sudden acceleration and braking, and altered intersection-crossing speeds and patterns.

CONCLUSIONS

The results suggest that GSCTs worsen safety at signalized intersections, and thus their removal should be considered.

Analysis of the Impact of Countdown Signal Timers on Driving Behavior and Road Safety

This article describes the safety and effectiveness issues related to signal countdown timers (SCT). These devices are used in many countries around the world. The impact of these devices on road safety and the effectiveness of traffic lights is presented. During a literature review, more than 18 aspects of device use were recognized. The research involved measurements carried out at three intersections in Płock (Poland). The initial and final period of the green signal for vehicles was analyzed. Headways, incidences of vehicles passing through after the end of the green signal, and red-light violations were examined. Additionally, a fuel consumption analysis and a case study of a road crash in Szczecin (Poland) are presented. Problems related to signal countdown timers working during traffic light failure are described. The research shows different influences of signal countdown timers at various intersections. It was observed that SCTs increase the number of red-light violations and during the red-amber signal. On the other hand, the number of entries during the amber signal with SCTs is lower. A literature review also indicated that the use of SCT causes a reduction of start-up time (positive impact) and increases vehicle speed (negative impact). The article concludes that SCTs do not always fulfill their role in improving road safety and control efficiency. Conclusions can address various stakeholders, including drivers, road authorities, and traffic engineers.

Effect of speed/red-light cameras and traffic signal countdown timers on dilemma zone determination at pre-timed signalized intersections

In this study, the dilemma zone types and lengths were studied according to their definitions based on Gazis, Herman, and Maradudin (GMH) and the probability-of-stopping models, and the link of the two models to each other was explored. Moreover, the effects of the joint and separate use of the speed/red-light camera (SRLC) and the traffic signal countdown timer (TSCT) on dilemma zone determination and safety were investigated. Multiple linear regression was conducted to define the minimum stopping and maximum passing distance boundaries, and binary logistic regression was conducted to define the boundary of dilemma zone type II based on the probability of stopping. The results show that SRLC significantly shifts the dilemma zone downstream and increases the probability of stopping by 11 %. TSCT was found not to have any significant effect on the dilemma zone, but it was found to increase the approaching speeds. It was also found that dilemma zone type II can capture all the dilemma zone types to a great extent.

Cyclists' adaptation to a countdown timer to green traffic light: A before-after field study

Countdown timers (CDTs) for pedestrians and cars have been shown to produce various effects, including improved efficiency and decreased safety. This study aimed to explore adaptive behaviours of cyclists towards a CDT to green traffic light, conducted as a before-after study in real traffic. Cyclists adapted to the CDT by searching for and using the information that it provided, mainly in terms of speed adaptation and glance behaviour. Start-up delays were reduced but there is a concern that red light violations could increase. There might be undesirable effects on crucial information intake in cases where the CDT was used not as a complement but as a substitute for the traffic light. The results essentially indicate that cyclists use the information provided by the CDT for their own efficiency, rather than for rule-based safety.

Innovative countermeasures for red light running prevention at signalized intersections: A driving simulator study

The change interval, which includes the yellow and all-red times, plays a crucial role in the safety and operation of signalized intersections. During this interval, drivers not only need to decide to stop or go but also have to interact with drivers both in front and behind, trying to avoid conflicting decisions. Red light running and inconsistent stopping behavior may increase the risk for angular and rear-end crashes. This study aims to investigate the effect of different innovative countermeasures on red light running prevention and safe stopping behavior at signalized intersections. Five different conditions were tested inviting sixty-seven volunteers with a valid driving license. The conditions include a default traffic signal setting (control condition), flashing green signal setting (F-green), red LED ground lights integrated with a traffic signal (R-LED), yellow interval countdown variable message sign (C-VMS), and red light running detection camera warning gantry (RW-gantry). Drivers in each condition were exposed to two different situations based on the distance from the stop line. In the first situation, drivers were located in the indecision zone while in the second situation they were located in the likely stopping zone. A series of logistic regression analyses and linear mixed models were conducted to investigate the overall safety effects of the different countermeasures. The probability of red light running (RLR) was significantly reduced for R-LED in both analyses (i.e. in the total sample, and in the sample of crossed vehicles). Moreover, a clearly inconsistent stopping behavior was observed for the flashing green condition. Furthermore, a unit increase in speed (kph) at the onset of yellow interval significantly increases the probability of RLR by 5.3 %. The study showed that R-LED was the most effective solution for improving red light running prevention and encouraging a consistent stopping behavior at the intersection. In conclusion, the R-LED and the RW-gantry treatments are recommended as effective tools to improve safety at signalized intersections.

Green wave for cyclists: Users' perception and preferences

Several innovative measures in traffic control applied in Europe have successfully improved the comfort and safety of cycling, among which is the green waves for cyclists. Consecutive traffic lights are synchronised to create a green wave, increasing comfort and decreasing waiting times and related deliberate red-light running. This study focused on exploring the user acceptance of green wave systems and the user evaluation of six distinct interface designs (i.e. numeric-based countdown, dot-based vertical countdown, dot-based clockwise countdown, LED line, LED road surface, on-bike speed indicator). Results indicate a preference for three systems: numeric-based countdown, LED line and LED road surface. Results also show a significant influence of nationality on the evaluation of the interfaces. Based on our findings, we argue that the numeric-based countdown represents the most promising option for future adaptive green wave implementations. The outcomes of the present study represent a useful evidence and guidance for researchers, designers and decision makers in the field of green waves, mobility and traffic safety.

Comparison of proposed countermeasures for dilemma zone at signalized intersections based on cellular automata simulations

The Type II dilemma zone describes the road segment to a signalized intersection where drivers have difficulties to decide either stop or go at the onset of yellow signal. Such phenomenon can result in an increased crash risk at signalized intersections. Different types of warning systems have been proposed to help drivers make decisions. Although the warning systems help to improve drivers' behavior, they also have several disadvantages such as increasing rear-end crashes or red-light running (RLR) violations. In this study, a new warning system called pavement marking with auxiliary countermeasure (PMAIC) is proposed to reduce the dilemma zone and enhance the traffic safety at signalized intersections. The proposed warning system integrates the pavement marking and flashing yellow system which can provide drivers with better suggestions about stop/go decisions based on their arriving time and speed. In order to evaluate the performance of the proposed warning system, this paper presents a cellular automata (CA) simulation study. The CA simulations are conducted for four different scenarios in total, including the typical intersection without warning system, the intersection with flashing green countermeasure, the intersection with pavement marking, and the intersection with the PMAIC warning system. Before the specific CA simulation analysis, a logistic regression model is calibrated based on field video data to predict drivers' general stop/go decisions. Also, the rules of vehicle movements in the CA models under the influence by different warning systems are proposed. The proxy indicators of rear-end crash and potential RLR violations were estimated and used to evaluate safety levels for the different scenarios. The simulation results showed that the PMAIC countermeasure consistently offered best performance to reduce rear-end crash and RLR violation. Meanwhile, the results indicate that the flashing-green countermeasure could not effectively reduce either rear-end crash risk or RLR violations. Also, it is found that the pavement-marking countermeasure has positive effects on reducing the rear-end risk while it may increase the probability of RLR violation. Lastly, the implementation of the proposed warning system is discussed with the consideration of connected-vehicle technology. It is expected that the dilemma zone issues can be efficiently addressed if the proposed countermeasure can be employed within connected vehicle technology.

A comparison of safety benefits of pedestrian countdown signals with and without pushbuttons in Michigan

OBJECTIVE

This study evaluated the safety impacts of pedestrian countdown signals (PCSs) with and without pushbuttons based on pedestrian crashes and pedestrian injuries in Michigan.

METHODOLOGY

This study used 10 years of intersection data-5 years before PCSs were installed and 5 years after they were installed-along with a comparison group, to evaluate the crash impacts of PCSs; at 107 intersections the PCS had a pushbutton and at 96 it did not. At these intersections, and at their comparison sites (where no PCS was installed), crash data (from 2004 to 2016) were examined, along with traffic and geometric characteristics, population, education, and poverty level data.

RESULTS

Intersections where PCSs with pushbuttons have been installed showed a 29% reduction in total pedestrian crashes and a 30% reduction in fatal/injury pedestrian crashes. Further, when considering only pedestrians age 65 and below, these respective reductions are 33 and 35%. Intersections with PCSs but without pushbuttons did not show any significant change in any type of pedestrian crash.

CONCLUSIONS

Although the Manual on Uniform Traffic Control Devices (Federal Highway Administration [FHWA] 2009 ) requires the use of PCSs at new traffic signal installations, this study suggests a safety benefit of installing PCSs with pushbutton at signals where a PCS without a pushbutton is present.

Spatial distribution of pedestrian-motor vehicle collisions before and after pedestrian countdown signal installation in Toronto, Canada

BACKGROUND

Pedestrian countdown signals (PCS) have been installed in many cities over the last 15 years. Few studies have evaluated the effectiveness of PCS on pedestrian motor vehicle collisions (PMVC). This exploratory study compared the spatial patterns of collisions pre and post PCS installation at PCS intersections and intersections or roadways without PCS in Toronto, and examined differences by age.

METHODS

PCS were installed at the majority of Toronto intersections from 2007 to 2009. Spatial patterns were compared between 4 years of police-reported PMVC prior to PCS installation to 4 years post installation at 1864 intersections. The spatial distribution of PMVC was estimated using kernel density estimates and simple point patterns examined changes in spatial patterns overall and stratified by age. Areas of higher or lower point density pre to post installation were identified.

RESULTS

There were 14 911 PMVC included in the analysis. There was an overall reduction in PMVC post PCS installation at both PCS locations and non-PCS locations, with a greater reduction at non-PCS locations (22% vs 1%). There was an increase in PMVC involving adults (5%) and older adults (9%) at PCS locations after installation, with increased adult PMVC concentrated downtown, and older adult increases occurring throughout the city following no spatial pattern. There was a reduction in children's PMVC at both PCS and non-PCS locations, with greater reductions at non-PCS locations (35% vs 48%).

CONCLUSIONS

Results suggest that the effects of PCS on PMVC may vary by age and location, illustrating the usefulness of exploratory spatial data analysis approaches in road safety. The age and location effects need to be understood in order to consistently improve pedestrian mobility and safety using PCS.

Countdown timers, video surveillance and drivers' stop/go behavior: Winter versus summer

This paper presents an analysis of drivers' stopping and traversing behaviors during inter-green periods. Eight intersections were observed in Changchun, China both with and without countdown timers and/or video surveillance during summer and winter. The impacts of the devices on the drivers' behavior were examined and compared between the two seasons from a safety perspective. During winter abrupt braking on icy road can be very dangerous. The analysis was performed by dividing the approach leg into 10m intervals up to 90m upstream from the stop line. Three impacts are studied, including the profile of approaching speeds, the stop/go decision, and the maximum acceleration and deceleration. The findings revealed that installing both a countdown timer and CCTV in summer, or either of the devices in winter can increase drivers' stopping tendency and hence reduce red-light violations. Especially on an icy road during winter, a countdown timer can help smooth decelerations, which tend to begin earlier than at the intersections without the device, reducing the incidence of sudden braking.

Logit-Based Analysis of Drivers' Crossing Behavior at Unsignalized Intersections in China

OBJECTIVE

This study aims to investigate the crossing behavior of straight-moving drivers when they encounter other straight-moving drivers at unsignalized intersections in China.

BACKGROUND

In China, when two vehicle drivers encounter at an unsignalized intersection, neither driver completely stops his or her vehicle in most cases. Instead, one driver gradually approaches the intersection and dynamically decides to either yield or preempt by gaming with the other vehicle. This process increases the probability of accidents.

METHOD

A total of 305 crossing cases were collected at an unsignalized intersection in Kunming City. Motion parameters were extracted from the video detection program designed by our research group. Based on a logistic regression method, we analyzed decision making moment of straight-moving drivers under crossing conditions, established crossing behavior models, and identified the main factors that affected drivers' decisions. In all, 68 cases observed at a separate intersection were used to validate the established models.

RESULTS

For crossing processes at unsignalized intersections in China, straight-moving drivers from the right side completed preemptive/yielding decisions at 1.3 s before reaching the crossing point. However, the majority of straight-moving drivers from the left side completed decisions at 1.1 s before reaching the crossing point. The most important parameter that influenced the drivers' decisions was the difference between the speeds of the two vehicles.

CONCLUSION

An effective method for preventing traffic conflict between two straight-moving drivers is to control the speeds of the vehicles before they enter the intersection.

APPLICATION

This study explores crossing behavior of straight-moving drivers and provides significant insights for controlling driver behavior.

Effects of digital countdown timer on intersection safety and efficiency: A systematic review

OBJECTIVE

To investigate the available evidence referring to the effectiveness of digital countdown timers (DCTs) in improving the safety and operational efficiency of signalized intersection.

METHODS

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement guidelines. Relevant literature was searched from electronic databases using key terms. Based on study selection and methodological quality assessment, 14 studies were included in the review. Findings of the studies were synthesized in a narrative analysis.

RESULTS

Three types of DCT had different effects on intersection safety and operational efficiency. Green signal countdown timers (GSCTs) reduced red light violations, type I dilemma zone distributions, and rear-end collision likelihood but increased crossing after yellow onset and had mixed impacts on type II dilemma zone distributions and intersection capacity. In contrast, red signal countdown timers (RSCTs) increased intersection capacity, although their effectiveness in reducing red light violations dissipated over time. Likewise, continuous countdown timers (CCTs) significantly enhanced intersection capacity but had mixed influences on red light violations and crossing after yellow onset.

CONCLUSIONS

Due to the limited and inconsistent evidence regarding DCTs' effects on intersection safety and efficiency, it is not sufficient to recommend any type of DCT to be installed at signalized intersections to improve safety and operational efficiency. Nevertheless, it is apparent that both RSCTs and CCTs enhance intersection capacity, though their impacts on intersection safety are unclear. Future studies need to further verify those anticipated safe and operational benefits of DCTs with enriched field observation data.

Exploring motorcycle red-light violation in response to pedestrian green signal countdown device

Literature has suggested that angle/rear-end collisions would arise from the reality that motorists and motorcyclists tended to accelerate aggressively in response to the remaining seconds of green signal countdown device (GSCD). One safety concern, while GSCD has gradually been removed for safety in Taiwan, is pedestrian green signal countdown device (PGSCD) that is used by approaching motorists and motorcyclists that may adopt the information to travel aggressively - an unintended consequence that is detrimental to safety. Research has reported that there appeared no negative effect of PGSCD on motorist behaviours but the effect on motorcyclists' behaviours has been rarely investigated. Using video/speed cameras, the current research investigates motorcyclists' RLV (red-light violation) behaviours. The descriptive analyses indicate that the percentage of RLV at PGSCD intersection is higher than that at typical intersection, and the violating motorcycles appear to have higher travelling speeds at PGSCD intersection. Several interaction terms were examined with the binary logit framework, and the results reveal that several factors are associated with RLV, notably male/young riders, moped/large motorcycle users, higher approaching speeds of motorcycles, those with tropical helmets, and lower traffic volume. Similar determinants of early-start behaviours (for those waiting at reds and could view the PGSCDs for the crossing pedestrians at the same time) were identified. Implications of the research findings, the concluding remarks, and recommendations for future research are finally provided.

Assessing the 'system' in safe systems-based road designs: using cognitive work analysis to evaluate intersection designs

While a safe systems approach has long been acknowledged as the underlying philosophy of contemporary road safety strategies, systemic applications are sparse. This article argues that systems-based methods from the discipline of Ergonomics have a key role to play in road transport design and evaluation. To demonstrate, the Cognitive Work Analysis framework was used to evaluate two road designs - a traditional Melbourne intersection and a cut-through design for future intersections based on road safety safe systems principles. The results demonstrate that, although the cut-through intersection appears different in layout from the traditional intersection, system constraints are not markedly different. Furthermore, the analyses demonstrated that redistribution of constraints in the cut-through intersection resulted in emergent behaviour, which was not anticipated and could prove problematic. Further, based on the lack of understanding of emergent behaviour, similar design induced problems are apparent across both intersections. Specifically, incompatibilities between infrastructure, vehicles and different road users were not dealt with by the proposed design changes. The importance of applying systems methods in the design and evaluation of road transport systems is discussed.

Evaluating time-reminder strategies before amber: common signal, green flashing and green countdown

The safety level of signalized intersection depends greatly on drivers' decision-making behaviors, which are significantly influenced by the time-reminder strategy before amber of the signal device. However, previous related studies are mainly based on the statistical results from the field data rather than explore the influence mechanism of the signal device on the signalized intersection's safety level. Therefore, this study aims to find out how these three typical signal devices with various time-reminder strategies, i.e., common signal device (CSD), green signal flashing device (GSFD), and green signal countdown device (GSCD), affect drivers' decision-making processes during the period from the end of the green phase to the onset of the red phase (i.e., G2R) and then evaluate their safety performance from the aspect of RLR violations. Firstly, an overall decision-making framework during G2R is presented to describe the driver-signal interaction and encloses four decision-making processes, which can be analyzed and modeled based on the field data collected from six signalized intersections in Changsha, China. Empirical analyses show that the time point of decision-making before amber under GSCD is the earliest and that under CSD is the latest, which can also be modeled and reproduced by back propagation neural network (BPNN). After that, five binary logistic regression models are developed to determine the safety effect during other various processes and results show that red-light-running (RLR) violations are not only dependent on the range of dilemma zones (DZ) but also substantially on stop and go decisions of those vehicles in DZ, both of which are the potential cause and direct factors to RLR violations and found to be significantly affected by the time-reminder strategy of the green signal device. Finally, although GSCD stimulates the drivers in DZ to choose to cross the intersection during amber, which produces a higher RLR risk compared with CSD and GSFD, the intersection with GSCD is verified to own the lowest RLR violations due to its greatly positive effect in cutting down the range of DZ.

Effect of audio in-vehicle red light-running warning message on driving behavior based on a driving simulator experiment

OBJECTIVE

Drivers' incorrect decisions of crossing signalized intersections at the onset of the yellow change may lead to red light running (RLR), and RLR crashes result in substantial numbers of severe injuries and property damage. In recent years, some Intelligent Transport System (ITS) concepts have focused on reducing RLR by alerting drivers that they are about to violate the signal. The objective of this study is to conduct an experimental investigation on the effectiveness of the red light violation warning system using a voice message.

METHODS

In this study, the prototype concept of the RLR audio warning system was modeled and tested in a high-fidelity driving simulator. According to the concept, when a vehicle is approaching an intersection at the onset of yellow and the time to the intersection is longer than the yellow interval, the in-vehicle warning system can activate the following audio message "The red light is impending. Please decelerate!" The intent of the warning design is to encourage drivers who cannot clear an intersection during the yellow change interval to stop at the intersection.

RESULTS

The experimental results showed that the warning message could decrease red light running violations by 84.3 percent. Based on the logistic regression analyses, drivers without a warning were about 86 times more likely to make go decisions at the onset of yellow and about 15 times more likely to run red lights than those with a warning. Additionally, it was found that the audio warning message could significantly reduce RLR severity because the RLR drivers' red-entry times without a warning were longer than those with a warning.

CONCLUSIONS

This driving simulator study showed a promising effect of the audio in-vehicle warning message on reducing RLR violations and crashes. It is worthwhile to further develop the proposed technology in field applications.

Estimating rear-end accident probabilities at signalized intersections: a comparison study of intersections with and without green signal countdown devices

OBJECTIVE

Rear-end accidents are the most common accident type at signalized intersections, because the diversity of actions taken increases due to signal change. Green signal countdown devices (GSCDs), which have been widely installed in Asia, are thought to have the potential of improving capacity and reducing accidents, but some negative effects on intersection safety have been observed in practice; for example, an increase in rear-end accidents.

METHODS

A microscopic modeling approach was applied to estimate rear-end accident probability during the phase transition interval in the study. The rear-end accident probability is determined by the following probabilities: (1) a leading vehicle makes a "stop" decision, which was formulated by using a binary logistic model, and (2) the following vehicle fails to stop in the available stopping distance, which is closely related to the critical deceleration used by the leading vehicle. Based on the field observation carried out at 2 GSCD intersections and 2 NGSCD intersections (i.e., intersections without GSCD devices) along an arterial in Suzhou, the rear-end probabilities at GSCD and NGSCD intersections were calculated using Monte Carlo simulation.

RESULTS

The results suggested that, on the one hand, GSCDs caused significantly negative safety effects during the flashing green interval, especially for vehicles in a zone ranging from 15 to 70 m; on the other hand, GSCD devices were helpful in reducing rear-end accidents during the yellow interval, especially in a zone from 0 to 50 m.

CONCLUSIONS

GSCDs helped shorten indecision zones and reduce rear-end collisions near the stop line during the yellow interval, but they easily resulted in risky car following behavior and much higher rear-end collision probabilities at indecision zones during both flashing green and yellow intervals. GSCDs are recommended to be cautiously installed and education on safe driving behavior should be available.

Exposure to lateral collision in signalized intersections with protected left turn under different traffic control strategies

This paper proposes an original definition of the exposure to lateral collision in signalized intersections and discusses the results of a real world experiment. This exposure is defined as the duration of situations where the stream that is given the right-of-way goes through the conflict zone while road users are waiting in the cross-traffic approach. This measure, obtained from video sensors, makes it possible to compare different operating conditions such as different traffic signal strategies. The data from a real world experiment is used, where the adaptive real-time strategy CRONOS (ContRol Of Networks by Optimization of Switchovers) and a time-plan strategy with vehicle-actuated ranges alternately controlled an isolated intersection near Paris. Hourly samples with similar traffic volumes are compared and the exposure to lateral collision is different in various areas of the intersection and various traffic conditions for the two strategies. The total exposure under peak hour traffic conditions drops by roughly 5 min/h with the CRONOS strategy compared to the time-plan strategy, which occurs mostly on entry streams. The results are analyzed through the decomposition of cycles in phase sequences and recommendations are made for traffic control strategies.

Effects of countdown timers on driver behavior after the yellow onset at Chinese intersections

OBJECTIVES

Few studies have focused on the effect of countdown timers at signalized intersections in China, where such timers are widely deployed for their perceived benefits of increased safety and capacity. This study examines the effect of countdown timers on driver behavior during the yellow interval.

METHOD

Signal phasing and traffic operations were videotaped at 4 comparable signalized intersections under normal conditions. Microscopic details were extracted manually at 25 Hz to yield 24 h of data on onset time of the yellow, onset time of the red, driver location and actions after the onset of the yellow, red light-running violations, etc. For comparable intersections with and without countdown timers, driver behavior measured by driver decision (stop or go) and vehicle entry time (when the vehicle crosses the stop line) were analyzed using binary logistical regression (BLR) and a nonparametric test, respectively.

RESULTS

The results suggest that countdown timers can indeed influence driver behaviors, in terms of decisions to stop or cross the intersection as well as the distribution of vehicle entry times. There was a strong correlation between the presence of countdown timers and an increase in red light violations.

CONCLUSION

Countdown timers may lead to increased entrance into the intersection during the later portions of the yellow and even the red. This alarming finding calls for further research as well as for serious consideration before the field deployment of countdown timers.