Signal Countdown Research Articles

Comparative and Microscopic Analysis of Vehicle Startup Behavior in Red Countdown Traffic Lights with Various Display Forms

Background: Countdown-type traffic lights provide drivers with the time remaining before the signal turns green or red. Most countdown devices inform the drivers of the exact signal switching time numerically on a display form. This study focuses on two vehicle startup behaviors when a red signal phase countdown (RC) is displayed: a premature start (PS) and an early reaction (ER). The PS is a vehicle crossing the stop line before the green phase, and the ER is a vehicle starting to move before the green phase. While there are many studies on PS rates under RC, there are only a few studies on ER rates. There are also few studies that have analyzed the relationship between the PS and ER rates and the display forms of RC have also been analyzed in terms of micro-behavior. Objective: This study microscopically analyzes the ER and PS by including data within 1 second at signal switching while comparing 10 types of display forms in RC in order to obtain the ideas of safer and more efficient display forms in signal countdown. Methods: We conducted the experiments with RC traffic lights of different display forms, and the surveys of no countdown (NC). Results: From the very limited conditions of the experiment, we found that there is a threshold at which the ER rates in RC and NC differ significantly. Conclusion: We were also able to analyze the basic characteristics related to the display forms of RC, which is a quick start and which reduces PS and ER.

Exploring the Influence of Signal Countdown Timers on Driver Behavior: An Analysis of Pedestrian–Vehicle Conflicts at Signalized Intersections

Although signal countdown timers (SCTs) are likely to enhance efficiency at signalized intersections, there is little research on how they affect road users’ behavior. The present study explores factors associated with driver behavior through two approaches to examine how SCTs influence drivers’ actions toward pedestrians violating red lights. In the first approach, through an on-road questionnaire survey, the self-reported behavior of 369 drivers when crossing an intersection enabled with SCTs was analyzed. In the second approach, the drivers’ behavior was studied through naturalistic driving studies at two signalized intersections equipped with SCTs in Babol, Iran. Analyzing vehicle–pedestrian conflicts indicated that the presence of SCTs had a significant influence on driving behavior. Also, the ending seconds of green lights, as critical times of the SCTs, led to changes in driving behavior. Increasing the vehicle speed, changing lanes, and concurrent increases of speed and changing lanes were the common driver actions affected by critical times of the SCTs. Finally, the effect of critical times on drivers’ actions during conflicts was modeled by using the binary and multinomial logistic methods. The results show that SCTs are an external factor that can lead to risky driver behavior, such as errors and violations that might increase the potential for pedestrian accidents.

Assessing the Impact of Safety Countermeasures on Dilemma Zones at Signalized Intersections of Urban Roads: a Driving Simulator Study

When drivers approach a signalized intersection at the start of the yellow signal, they might be reluctant to decide whether to stop or go through the intersection due to the dilemma zone (DZ), with the consequent risk of improper behaviors that can lead to rear-end collisions and right-angle crashes. The main goal of this research is to analyze the driver's behavior at the onset of the yellow signal and to identify the most effective countermeasures for the resolution of the dilemma zone in order to improve the safety and efficiency of urban signalized intersections. A driving simulator study was carried out, and three different countermeasures were specifically designed and tested: Green Signal Countdown Timers (GSCT) (C1); a new scheme of vertical and horizontal warning signs (C2); and an in-vehicle advanced driving assistance system that uses Augmented Reality (AR) and connected vehicle technologies (C3). Forty-six volunteers took part in the experiments, driving the same scenario four times (three with countermeasures and one as a baseline condition). The results demonstrated that with countermeasure C1, the length of the DZ increased with respect to the baseline condition; moreover, the stop/go drivers’ decisions were found to be more inconsistent, increasing the potential risk of rear-end crashes. Conversely, countermeasures C2 and C3 resulted in a reduction of DZ length (-30.5% and 21.6%, respectively); in addition, C2 was found to be the one that recorded the greatest consistency of drivers’ decision-making behaviors, while C3 provided the drivers with timely and personalized early-stop warnings and recorded fewer wrong behaviors. Based on the results of this study, C2 and C3 countermeasures might be a good way to improve safety and operations at urban signalized intersections and cut down on the number of drivers who aren't sure what to do when the yellow light comes on.

User Comprehension of Bicycle Signal Countdown Timers

For a person on a bicycle at signalized intersections, trail crossings, or midblock locations, knowing how long they must wait to receive a green indication is valuable information. In the international context, this information is often provided by small, nearside bicycle signal heads that contain a countdown display that visually conveys the amount of waiting time. This paper presents the results of research to investigate the comprehension of bicycle countdown timer displays in the U.S. context. The study conducted an online survey to analyze the understanding and preference of three alternative bicycle countdown timer displays. Respondents were recruited by two recruitment methods: mailed postcards (568 responses) and social media ads (772 responses). A countdown timer with circular disappearing dots was then installed at an intersection in Portland, OR, and an intercept survey was conducted of users (29 responses). For both surveys, comprehension rates were established by coding an open-ended response to a question about the display's intended meaning. The surveys found that the bicycle signal countdown displays were intuitive, and the intended meaning was fully understood by over 60% of online survey respondents and 52% of the intercepted bicyclists. Partial comprehension increased to over 70% and 97% of those intercepted, respectively, which would result in safe user interpretation. A countdown timer may also improve the waiting experience for stopped bicyclists, as 70% of respondents strongly or somewhat agreed that they would feel better about waiting at an intersection if a bicycle countdown timer was present.

An empirical analysis of the effect of pedestrian signal countdown timer on driver behavior at signalized intersections

A pedestrian countdown signal (PCS) is designed to provide additional information to pedestrians at crossings and help their crossing decisions. However, the PCS information can also affect drivers’ behaviors when it is visible to drivers. With the countdown information visible to drivers, they can know the timing of the onset of the upcoming yellow and red traffic lights. This unintended information might cause changes in driving behaviors such as early stops, speeding, or abrupt accelerations to cross an intersection before the red light. Current literature has mainly focused on the drivers’ crossing decisions or the number of crashes before and after displaying a PCS at intersections. However, there is a paucity of studies that investigate drivers’ behaviors when approaching signalized intersections equipped with a PCS. This paper investigates vehicle speed patterns, safety implications, and the factors influencing driving behaviors at intersections before and after displaying the countdown information. To do so, we collected and extracted video-based vehicle trajectory data from 5,000 vehicles at signalized intersections with and without a PCS in the City of Montreal, Canada. The observed data provide the median and 85th centile approaching speed, the intersection entering speed, as well as safety implications regarding the countdown information. The multilevel mixed-effect model and Tukey’s test conduct statistical comparisons across intersections and signal phases. The study results demonstrate that drivers cross intersections at a higher speed when the pedestrian countdown information is visible to drivers. Moreover, the vehicles at the same intersection with a PCS show clearly different speed patterns before and after the onset of the countdown timer. After controlling other factors, the mixed-effect model results further indicate displaying a PCS to drivers increase the approaching speed by approximately 11 km/h.

The effects of green signal countdown timer and retiming of signal intervals on dilemma zone related crash risk at signalized intersections under heterogeneous traffic conditions

During yellow intervals, dilemma zones (DZ) often trigger red light violations (RLV) and unexpected stoppings near stop lines, causing severe collisions at signalized intersections. While several studies in developed countries have tested various countermeasures to eliminate DZ, this aspect is not well explored for developing countries. This study investigated a green signal countdown timer’s (GSCT) efficacy in reducing DZ at signalized intersections. Based on historical crash data, 10 signalized junctions in Delhi, India, 5 with GSCT and 5 without, were chosen. Although India has a permissive yellow law, all the study sites have a flat 5 s yellow change interval with no provision of all-red (AR) intervals, which might have resulted in severe crashes at these locations. Empirical assessments revealed that GSCT minimizes the length of type-I DZ, which refers to a situation when drivers can neither stop nor proceed to the intersection during the yellow signal. Interestingly, GSCT also minimizes the length of type-II DZ, which is an indecision zone based on drivers’ 10% and 90% stopping probabilities. Summation of yellow and all-red intervals (Y + AR) obtained using Institute of Transportation Engineers (ITE) equations was found to be longer than field-allocated 5 s change interval at GSCT-enabled sites. Consequently, GSCT’s effectiveness across various yellow and all-red intervals was investigated in the PTV-VISSIM microsimulation tool, and crossing and rear-end conflicts were extracted using Surrogate Safety Assessment Model (SSAM). Results suggest that GSCT’s presence, along with estimated yellow and all-red intervals, reduces crossing and rear-end conflicts due to RLVs and inconsistent stoppings, respectively.

An evaluation of the effectiveness of countermeasures for improving the safety of dilemma zones: A driving simulator study

The main objective of this driving simulator study is to analyze the behavior of the driver at the start of the yellow signal of a signalized rural intersection and identify the most effective countermeasures for tackling the dilemma zone, namely an area on the intersection approach where vehicles at the start of the yellow phase can neither safely stop before the stop line nor cross the intersection. The following countermeasures were tested in the study on a sample of 48 drivers: green signal countdown timers, GSCT (C1); a new pattern of vertical and horizontal warning signs (C2); and an advanced on-board driver assistance system based on augmented reality (AR) and connected vehicle technologies (C3). These countermeasures were tested and compared to a baseline condition (B) where no countermeasures were applied. Based on the results of this study, the C2 and C3 countermeasures have proven to be valid tools for reducing driver indecision when approaching signalized intersections at the start of the yellow signal. In fact, using C2 and C3, the length of the dilemma zone was equal to 30 m and 36 m, respectively, with a reduction of about 50%, as compared to the baseline condition (B). Moreover, a reduced number of false behaviors was recorded, as well as a greater consistency in driver decision-making behaviors. Conversely, the C1 countermeasure did not lead to a significant improvement in the dilemma zone: an unnecessary increase in early stop rates was recorded, resulting in reduced intersection efficiency and operations.

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 Behavior Characteristics for Pedestrian Twice-Crossing at Signalized Intersections Based on an Improved Social Force Model

At urban signalized intersections, pedestrian twice-crossing is usually viewed as a complex human behavior, since there are many factors influencing it. Mostly, pedestrians engage in a complicated cognitive process of perception, attention and decision-making. Therefore, it is necessary to identify the major factors affecting this behavior, and develop an effective pedestrian dynamic model, in order to increase the safety and efficiency of crossing streets. This study proposes a force-based model of pedestrian dynamics by improving the classic social force model, in order to determine the influencing factors and quantify the forces acting on pedestrians crossing in two stages at signalized intersections. Through analyzing the characteristics of pedestrian twice-crossing behavior, the social force model was enhanced by providing a new component of the green signal countdown. The improved model includes four parts of the self-driving force in the ideal state, the repulsive and attractive forces generated by surrounding pedestrians, the resistance of the crosswalk boundary line, and the force produced by the green signal countdown. Each part was considered with qualitative analysis and quantitative calculation. The results show that the proposed model can achieve high accuracy in measuring the forces acting on pedestrian twice-crossing. The findings of this study have great implications for designing pedestrian facilities and optimizing pedestrian signal timings, helping thus to increase the mobility and safety of pedestrian twice-crossing.

Exploring the Influence of Signal Countdown Timers (Scts) on Driver Behaviour: An Analysis on Pedestrian-Vehicle Conflicts at Signalized Intersections

Exploring the Influence of Signal Countdown Timers (Scts) on Driver Behaviour: An Analysis on Pedestrian-Vehicle Conflicts at Signalized Intersections

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.

A computer vision algorithm for locating and recognizing traffic signal control light status and countdown time

It is of practical importance for individual vehicles to automatically identify traffic signal light status to facilitate their decision makings for traffic safety performance enhancement and operation efficiency maximization when they are approaching intersections, especially in near-future fully-or semi-autonomous vehicle-penetrated traffic systems. Traditional methods aim to directly extract information from the light emitting area of a traffic signal light head, but this can easily result in missed or false signal light status identification due to changes in detection distance and lighting conditions. To address these research gaps, an innovative computer vision-based algorithm is developed for signal control light status identification and countdown time recognition. Based on the unique characteristics of black traffic light boards, color segmentation is conducted in both RGB and HSV channels, and traffic light boards and countdown time display boards are located through cascade filtering algorithms. In the HSV color space, the H component can be extracted and highlighted to determine the current signal status by distinguishing the distribution of the pixel points of the H component. Based on the nearest neighbor interpolation algorithm, an adaptive threading method is developed to improve countdown time recognition. The experimental tests were conducted to verify the effectiveness of the developed approach under various scenarios with acceptable recognition accuracy and execution efficiency. The developed approach can be applied and integrated with other detection and control algorithms to strengthen vehicle-crossing safety performance and operational efficiency at intersections.

Evaluating the Performance of Signalized Intersection with Signal Countdown Timer

Signalized intersections are the interrupted traffic flow facility in a roadway network. The efficiency of traffic operations at the signalized intersection is expected to improve during inter-green intervals. To improve the quality of service at an intersection the traffic control devices are used widely over the world. The time intervals defined for traffic signal operation help to reduce severe traffic conflicts, delay, and improve driver’s decision for making turns. The present study evaluates the performance of traffic operations under with and without signal countdown timer (SCT) conditions based on field data collected at two signalized intersections in Hyderabad city, India. The vehicles speeding behavior and drivers complying with traffic regulation are also analyzed under different countdown timer conditions. It has been found that the average approaching speed of vehicles and red-light violations are found to be changed due to changes in the signal countdown timer conditions. The average startup loss time calculated in the field was found to be decreased when SCT was inactive. A significant increase in the capacity of signalized intersections has been observed when SCT was active. The traffic performance measures such as average control delay and queue lengths as estimated on the approaches were influenced due to the presence of STCs. The study finds that the signal countdown timer is an effective device that can enhance the traffic safety and operational performance of a signalized intersection.

Red light running behavior of bicyclists in urban area: Effects of bicycle type and bicycle group size

Bicyclists are vulnerable to fatality and severe injury in road crashes. Red light running violation of bicyclists is the major contributory factors to the crash involvement of bicyclists worldwide. This study aims to identify the factors that affect the propensity of red light running of bicyclists. Effects of bicycle type and bicycle group size are considered. Video observation surveys were conducted at eight signalized intersections in the urban area of Nanjing City in China. Crossing behaviors of 6,930 bicyclists were recorded. Then, a random-parameter logit model was established to measure the association between the propensity of red light running of bicyclist and possible factors. Results indicated that the propensity of red light running of e-bike riders was significantly higher than that of conventional bicyclists. Additionally, factors including bicyclists’ demographics, bicycle group size, traffic flow condition, road geometry and traffic control attributes also affected the propensity of red light running of bicyclists. Propensity of red light running of bicyclist decreased with the increase in the bicycle group size. Propensity increased with the increase in bicycle volume but declined when the opposing traffic volume increased. Presence of signal countdown display was correlated to the increase in the propensity of red light running. Furthermore, interaction effects between bike type and factors including bicyclists’ age, bicycle group size and bicycle volume on the propensity of red light running were significant. These findings can enhance the understanding of red light running behaviors of bicyclists. Also, useful recommendations that can deter against red light running behaviors and enhance overall road safety were provided.

Investigation of environmental benefits of traffic signal countdown timers

The traffic demands in major cities are increasing, causing significant congestion and greenhouse gas (GHG) emissions around signalized intersections. Many researchers have attempted to mitigate these effects by optimizing traffic signal systems, but this study introduces a red time traffic signal countdown timer (TSCT) to help drivers decide to control vehicle idling and investigates its environmental benefits. The research framework consists of three modules: the development of a drivers’ behavior model; implementation of vehicle idling control; and the estimation of GHG emissions. This framework has been materialized in Haeundae-gu in Busan, Korea as a case study. The results revealed reductions of GHG emissions by 10.9% and 56.8% of the stationary and idling vehicles, respectively, proving the environmental benefit of the red time TSCT with the drivers’ voluntary involvement. This study presents a logical basis for the assertive deployment of the red time TSCT in major cities suffering from GHG emissions.

Analysis of Crossing Behavior and Violations of Electric Bikers at Signalized Intersections

This paper focuses on investigating electric bikers’ (e-bikers) crossing behavior and violations based on survey data of 3,126 e-bikers collected at signalized intersections in Nantong, China. We first explore e-bikers’ characteristics of late crossing, incomplete crossing, and violating crossing behaviors by frequency analysis and duration distribution, and examine a few influential factors for e-bikers’ red-light running (RLR) behavior, including site type, crossing length and traffic signal countdown timers (TSCTs). E-bikers’ RLR behavior is further divided into three categories, namely GR near-violations, RR violations, and RG violations. Second, we use a binary logistic regression model to identify the relationship between e-bikers’ RLR behavior and potential influential factors, including demographic attributes, movement information, and infrastructure conditions. We not only make regression analysis for respective violation type, but also carry out an integrated regression of a census of all three types of violations. Some insightful findings are revealed: (i) the green signal time and site type are the most significant factors to GR near-violations, but with little impact on the other two violation types; (ii) the waiting time, waiting position, passing cars and crossing length exert considerable impact on RR violations; (iii) for RG violations, TSCTs, leading violators and gender are the most significant factors; (iv) it is also unveiled that site type, green signal time and TSCTs have negligible impact on the whole violations regardless of the violation types. Thus, it is more meaningful to investigate the impacts of these variables on e-bikers’ RLR behavior according to different violation types; otherwise, the potential relationship between some crucial factors and e-bikers’ RLR behavior might be ignored. These findings would help to improve intersection crossing safety for traffic management.

Influence of green signal countdown timer on severe crash types at signalized intersections due to red light violations

ABSTRACT Traffic conflicts at signalized intersections caused by red light violations (RLVs) present an enormous danger for severe crashes. This study proactively evaluates the efficacy of Green Signal Countdown Timer (GSCT) on RLVs and resulting right-angle and right turn related crashes (for left-hand driving) using Post Encroachment Time (PET). A before-after (B-A) with comparison group analysis is done considering five 4-legged signalized intersections from Delhi, India comprising of with and without SCT installations. RLV occurrences and maximum violation time during initial 10 s of red are more in the absence of GSCT. Considering various RLV-related characteristics, Powered Two Wheelers (P2W) are found to have the highest exposure in crash involvement for both timer conditions. Finally, B-A method shows 57.74% reduction in crossing conflicts due to the presence of GSCT at the sites. . Accordingly, SCT's installation can be recommended as a cost-effective engineering countermeasure to reduce severe crash types at signalized intersections.

Exploring the impact of signal types and adjacent vehicles on drivers’ choices after the onset of yellow

Drivers’ choices at signalized intersections may be made in great uncertainty after the onset of yellow, which creates potential hazards for road safety. These choices are analyzed and modeled based on field observations at three comparable signalized intersections in Changsha, China. The results show that intersections without monitoring devices widen the indecision zone, which can increase the risk of rear-end collisions and the uncertainty of drivers’ decision-making. In addition, drivers are more likely to stop during the yellow interval at intersections equipped with a green signal countdown device (GSCD) than at those with a green signal flashing device (GSFD). Subsequently, according to the results of a binary logistic regression model (BLRM), drivers’ decision making at the onset of the yellow indication is greatly influenced by the vehicle’s spot speed, the distance to the stop line, and signal and monitoring devices. The presence of an adjacent vehicle with a short space headway can particularly motivate the following driver to make a go-decision after the first driver chooses to pass the intersection. However, a stop-decision by a driver in an adjacent lane can also prompt the following driver to stop.

An Eco-Driving Advisory System for Continuous Signalized Intersections by Vehicular Ad Hoc Network

With the vehicular ad hoc network (VANET) technology which support vehicle-to-vehicle (V2V) and vehicle to road side unit (V2R/R2V) communications, vehicles can preview the intersection signal plan such as signal countdown message. In this paper, an ecodriving advisory system (EDAS) is proposed to reduce CO2 emissions and energy consumption by letting the vehicle continuously pass through multiple intersections with the minimum possibilities of stops. We extend the isolated intersection model to multiple continuous intersections scenario. A hybrid method combining three strategies including maximized throughput model (MTM), smooth speed model (SSM), and minimized acceleration and deceleration (MinADM) is designed, and it is compared with related works maximized throughput model (MaxTM), open traffic light control model (OTLCM), and predictive cruise control (PCC) models. Some issues for the practical application including safe car following, queue clearing, and gliding mode are discussed and conquered. Simulation results show that the proposed model outperforms OTLCM 25.1%~81.2% in the isolated intersection scenario for the CO2 emissions and 20.5%~84.3% in averaged travel time. It also performs better than the compared PCC model in CO2 emissions (19.9%~31.2%) as well as travel time (24.5%~35.9%) in the multiple intersections scenario.