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Assessing Drivers’ Tailgating Behavior and the Effect of Advisory Signs in Mitigating Tailgating

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A human factors study was carried out to assess drivers' tailgating behavior and the effect of advisory signs in mitigating tailgating. Tailgating is a dangerous driving behavior and a leading cause of most rear-end crashes. Through a prior study, serious tailgating was identified on urban Rhode Island highways. It is critical to many urban traffic management authorities to understand tailgating and to explore means to mitigate drivers' tailgating behavior, especially on urban highways with high-speed and high-volume traffic. Properly designed advisory signs could reduce tailgating and related motor crashes. To assess drivers' behavior with regards to tailgating, a questionnaire survey was developed and given to a number of subjects with daily highway driving experience. The survey is designed to identify causes of tailgating and drivers' perceptions and engagements on tailgating behavior. Drivers' driving behaviors were further assessed through driving simulation under different traffic conditions. To help mitigate tailgating behavior, advisory signs and an educational video were developed. The effectiveness of these proposed counter-tailgating measures was assessed in the driving simulation. Subjects' real driving behaviors were further studied in a follow-up field study. Study results found that the majority had an incorrect sense regarding safe following distance and were tailgating while driving on highways. Heavy traffic was identified as the top tailgating cause. The simulation results confirmed the tailgating phenomenon observed on urban Rhode Island highways. The proposed advisory signs were found effective in mitigating tailgating behavior.
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PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
583
ASSESSING DRIVERS' TAILGATING BEHAVIOR AND
THE EFFECT OF ADVISORY SIGNS IN MITIGATING TAILGATING
Jyh-Hone Wang & Miao Song
Department of Mechanical, Industrial and Systems Engineering, University of Rhode Island
Kingston, Rhode Island, USA
E-mail: jhwang@egr.uri.edu
Summary: A human factors study was carried out to assess drivers' tailgating
behavior and the effect of advisory signs in mitigating tailgating. Tailgating is a
dangerous driving behavior and a leading cause of most rear-end crashes.
Through a prior study, serious tailgating was identified on urban Rhode Island
highways. It is critical to many urban traffic management authorities to
understand tailgating and to explore means to mitigate drivers’ tailgating behavior,
especially on urban highways with high-speed and high-volume traffic. Properly
designed advisory signs could reduce tailgating and related motor crashes. To
assess drivers' behavior with regards to tailgating, a questionnaire survey was
developed and given to a number of subjects with daily highway driving
experience. The survey is designed to identify causes of tailgating and drivers’
perceptions and engagements on tailgating behavior. Drivers' driving behaviors
were further assessed through driving simulation under different traffic
conditions. To help mitigate tailgating behavior, advisory signs and an
educational video were developed. The effectiveness of these proposed counter-
tailgating measures was assessed in the driving simulation. Subjects’ real driving
behaviors were further studied in a follow-up field study. Study results found that
the majority had an incorrect sense regarding safe following distance and were
tailgating while driving on highways. Heavy traffic was identified as the top
tailgating cause. The simulation results confirmed the tailgating phenomenon
observed on urban Rhode Island highways. The proposed advisory signs were
found effective in mitigating tailgating behavior.
INTRODUCTION
Tailgating, or following with insufficient vehicle headway, is a severe form of aggressive driving
(Sarkar et al, 2000) and a leading cause of rear-end crashes (Carter et al, 1995). According to the
National Center for Statistics and Analysis (NCSA, 2010), out of an annual average of 5.9
million police-reported automobile accidents in the US during 2006-2008, rear-end crashes
ranked the highest, with more than 1.8 million cases (30.4%), and resulted in more than 2,200
fatalities and approximately one-half million injuries each year. Two factors are primarily
responsible for rear-end crashes: inattention and tailgating (Dingus et al, 1997), while the latter is
the major contributing cause with a deadly consequence (Carter et al, 1995). To assess the
tailgating issue on urban Rhode Island highways, traffic surveillance videos collected at three
sites within the Providence metropolitan area were analyzed in a prior study conducted by the
authors (Song and Wang, 2010). According to driver’s reaction time, a quantified safe following
distance has been given in the form of a “2-second rule” that a driver is advised to keep a vehicle
headway of at least two seconds between his or her own car and the vehicle ahead. Driving with
a vehicle headway less than 2 seconds is thus considered "tailgating". The results of the study
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
584
revealed a serious tailgating situation on urban Rhode Island highways where more than 60% of
drivers were tailgating during rush hours and 40% during non-rush hours.
To reduce tailgating and associated crashes, counter-tailgating measures are needed to help
drivers maintain proper vehicle headway. Counter-tailgating measures such as advisory signs,
pavement markings, and enforcement by the police were recommended in Hutchinson’s study
(2008) to help reduce rear-end crashes. Rama and Kulmala (2000) investigated the effects of two
dynamic message signs (DMS) on driver’s car-following behavior. Results showed that a sign
about slippery road conditions reduced the mean speed by 1-2 km/hour in addition to the
decrease caused by the adverse road conditions. Another sign about minimum following distance
reduced the proportion of cars with a headway of less than 1.5 seconds by more than 30%, in
addition to a speed reduction of 1 km/h. Michael et al. (2000) collected tailgating data in an
urban setting from over 25,000 drivers and assessed the effectiveness of two hand-held roadside
signs admonishing drivers not to tailgate. The research found that the sign with a reference to
crashes had a greater impact on drivers, increasing the average headway by 0.18 seconds, when
compared to the other one.
To help drivers gauge their following distances, the effects of regularly-spaced markings on
highway pavement were assessed. Helliar-Symons, Webster and Skinner (1995) studied
pavement chevrons on a U.K. motorway. The markings were implemented with signs advising
drivers to keep 2-second vehicle headways. The results were encouraging with a large reduction
(56%) in crashes at the study site. Tailgating treatment programs employing the “dot” markings
were pilot-tested in Pennsylvania and Minnesota. PENNDOT’s program was honored in 2001
with the National Highway Safety Award. On a portion of US route 11 that previously
experienced high rates of tailgating, aggressive driving and tailgating dropped 60% after the
implementation of reflective dots and advisory signs that help motorists gauge their distance
behind leading vehicles (Roadway Safety Foundation, 2001). A similar project was piloted in
Minnesota in 2006 to educate motorists on how to maintain a minimum safe following distance
and to ultimately reduce rear-end crashes. Similar engineering elements to the Pennsylvania
program were used. Headway data collected prior to and after the treatments showed that the
average headway increased by 0.26 seconds, or 22.89 feet (Minnesota DOT, 2008).
Studies above demonstrated the effectiveness of advisory signs and pavement markings in
reducing tailgating. Although measurable benefits of the treatments were identified, there were
reported complaints about the pavement markings as they might distract drivers. Compared to
pavement markings, advisory signs are less intrusive and distractive to drivers and are easier to
implement and maintain. Given these advantages, a few advisory signs were proposed in this
study and their effects in mitigating tailgating were assessed through a driving simulation.
DESCRIPTION OF THE STUDY
A questionnaire survey was employed to collect drivers’ perceptions regarding tailgating and to
assess their driving behavior. A driving simulation study was developed to assess drivers’ real-
time driving behavior and their responses to proposed counter-tailgating.
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
585
Assessing Drivers’ Perception and Behavior regarding Tailgating
A nineteen-question questionnaire was designed to identify the causal factors of tailgating (Song
and Wang, 2010). Through participants’ responses, it expected to gain insights about drivers’
experiences and perceptions regarding tailgating on urban highways and their attitudes toward
tailgating when they were either actively or passively involved. The survey was presented as
PowerPoint slides on a laptop computer. Subjects made their answers via mouse and keyboard or
via verbal responses given to the research assistant. A total of 210 subjects participated in the
survey. Age and gender percentages of the survey resembled the Rhode Island population.
Subjects who took the survey were invited to participate in a driving simulation experiment in
the Driver Performance Lab at the University of Rhode Island. A fixed-base driving simulator
(L-3Com, Inc.) consisting of a regular vehicle module and three 42-inch plasma monitors with
1024 x 768 image resolution was used in the simulation. Five networked computers generate the
simulation by processing the driver’s inputs to the vehicle’s controls while perpetually updating
the audio stream and the driving scene on four visual channels. Three of the channels display the
drivers’ forward view of 180° and one supports the LCD front panel. Subjects interacted with the
simulator using the steering wheel and pedals that provided force feedback. Through an 8-minute
highway driving scenario with a speed limit of 65 mph, the simulation first assessed participants’
baseline driving behavior in its 1st trial. Subjects were asked to drive as he or she does in real life.
Assessing the Effect of Advisory Signs as Counter-Tailgating Measures
Counter-Tailgating Measures. Among several alternatives, two advisory messages were selected
to be tested through driving simulation, one was “Keep Minimum 2 Seconds Apart” and the
other was “Keep a Safe Following Distance”. The first message, similar to those of the
Minnesota tailgating project, used the words “2 Seconds” to alert drivers about the 2-second
vehicle headway. Rather than the quantitative advice given in the first message, the second
message used a qualitative advice. A subject would go through the highway driving scenario
again with the advisory message posted on either a static roadside sign or an overhead DMS at
the beginning of the scenario. The subjects were further asked to repeat the driving simulation
experiment after viewing an 1-minute educational video to help them better guage their vehicle
headways. With both auditory and visual instructions, the video instructed the subjects to use a
roadside reference point, such as a sign or a marking pole, to gauge the vehicle headway, and to
slow down if headway was less than 2 seconds. The effect of the educational video was assessed
through vehicle headway measurements taken in this run of the driving simulation.
Design of Experiment. The driving simulation experiment was developed and designed to
investigate two types of factors: main factors and blocking factors as shown in Table 1.
Table 1. Driving simulation experiment factors and levels
Factors Levels
Main Factors
Advisory Sign No Sign, With Sign
Educational Video No Video, With Video
Advisory Message “Keep Minimum 2 Seconds Apart”, “Keep a Safe Following Distance”
Type of Sign Static Roadside Sign, Overhead DMS
Blocking Factors Traffic Light, Heavy
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
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Each subject participated in the driving simulation experiment took three trials. Table 2 depicts
the setting of theses three trials. This experiment design would allow a pairwise comparison
among different trials to assess the effects of the advisory signs and the educational video.
Traffic condition was introduced as a blocking factor. In each trial, a subject could start driving
with heavy traffic which changed halfway to light traffic and vice versa by random assignment.
Table 2. Use of advisory signs and an educational video in the three trials
Trial 1st Trial 2nd Trial 3rd Trial
Advisory sign present No Yes Yes
Watch educational video before the trial No No Yes
To assess the design of advisory signs including advisory message and type of sign, subjects
were randomly divided into four equal-sized groups where different advisory signs were
evaluated. The four groups were shown in Table 3.
Table 3. The four experiment groups
Group Advisory sign evaluated
1 “Keep a Safe Following Distance” on a static roadside sign
2 “Keep Minimum 2 Seconds Apart” on a static roadside sign
3 “Keep a Safe Following Distance” on a DMS
4 “Keep Minimum 2 Seconds Apart” on a DMS
Analysis of Experiment. About 1 minute into the scenario, there is a fixed sign zone where
advisory signs were presented (empty zone for the 1st trial). A subject’s driving behavior was
recorded from this point until the completion of the simulation. In each trial, 8 vehicle headway
measurements were taken at random points (4 per traffic condition), and a total of 24 headway
data points were collected for each subject. Analysis of variance (ANOVA) was conducted to
investigate the effect of the main and blocking factors on vehicle headways. The effect of the
advisory signs was assessed by comparing vehicle headways collected between the 1st and the 2nd
trials. Headways from the 2nd trial were used to assess the effect of advisory message and the
type of sign and the interaction between them. The effectiveness of the educational video were
examined by comparing vehicle headways collected between the 2nd and the 3rd trials. Traffic
condition was assessed as a blocking factor in each ANOVA. A significant level of 0.05 was
used in all cases.
Field Study. Twelve subjects who participated in the driving simulation experiment partook a
follow-up field study. It allowed a comparison to be made between participants’ driving behavior
in the simulation and in real driving . In the 10-minute field study, each subject drove his or her
own vehicle accompanied by a research assistant. All subjects took the same route by entering I-
95 South from Exit 15 in Rhode Island and leaving at Exit 12. Then they returned to I-95 North
through the reverse order back to their starting point. They were advised to stay in the inner lanes
while driving on the highway to avoid traffic entering and exiting the highway and to maintain a
2-second vehicle headway following the instructions given in the educational video. The whole
driving process was recorded from the driver's view. Eight headways were randomly collected
from the video of each subject, four on each bound.
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
587
RESULTS AND DISCUSSIONS
Assessing Drivers’ Perception and Behavior regarding Tailgating
In the questionnaire, subjects’ understandings and perceptions of tailgating issue were surveyed.
Distraction, speeding, and tailgating were considered as the top three leading causes of crashes,
followed by road rage, DUI, changing lane without signaling, running red lights, etc. “Heavy
traffic”, “slow car ahead of my vehicle”, and “I am in a hurry” were the top three causes for
tailgating. The majority (84.3%) indicated that they were affected by tailgaters but reacted
passively as indicated by their top choices “change lanes to let the tailgater pass” (34.1%).
Most subjects (70.0%) indicated that they did not usually follow others while driving on
highways and 73.8% agreed that keeping safe vehicle headway was very important. The majority
(77.1%) thought that they knew what the proper vehicle headway was and kept a safe headway
most of the time (90.5%). From these results, it did not appear that a serious tailgating problem
existed. When asked how much distance they maintain when driving at 60 mph on highways,
94.8% of subjects indicated that they maintained less than 11 car lengths, and almost half
maintained less than 4 car lengths. A 2-second headway requires a distance of 11 car lengths at
60 mph (assuming a car length of 15 feet), therefore a severe tailgating issue was revealed as
most drivers were probably tailgating without knowing they were doing so. Subjects’ opinions
were reliable since 78.6% of them preferred using car length over time to gauge headway.
The findings found from the survey indicated that the majority of Rhode Island drivers had an
incorrect sense regarding safe vehicle headway and were following other vehicles too closely on
highways (Song & Wang, 2010). Through the baseline test (1st phase) of the driving simulation,
it found that the average vehicle headway kept by subjects was 1.02 seconds, half of the safe
following distance. Figure 1 shows vehicle headway distributions in different traffic conditions.
It shows that almost all subjects participated in driving simulation were tailgating. Heavy traffic
caused subjects to further decrease their vehicle headways. Both the survey and the simulation
confirmed the serious tailgating on urban Rhode Island highways identified in the prior study.
Figure 1. Distributions of the collected vehicle headways in light traffic (left) and in heavy traffic (right)
from the baseline test of driving simulation
Assessing the Effect of Advisory Signs as Counter-Tailgating Measures
A total of 36 licensed drivers participated in the simulation study. None of them had previous
experience with a driving simulator. Vehicle headway statistics are shown in Table 4.
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
588
Table 4. Vehicle headway statistics (in seconds) by group and trial
Group 1st Phase 2nd Phase 3rd Phase
Mean Std Mean Std Mean Std
1 1.06 0.33 1.15 0.45 2.05 0.27
2 0.92 0.48 1.11 0.53 1.99 0.34
3 1.00 0.31 1.29 0.41 2.18 0.40
4 1.08 0.43 1.40 0.50 2.07 0.31
Total 1.02 0.42 1.24 0.48 2.07 0.35
The effect of the presence of the advisory signs was assessed through ANOVA on the 1st phase
(w/o advisory signs) and the 2nd phase (with advisory signs) data. The results showed that the
presence of the advisory sign was a significant factor (p = 0.000) as the average headway
increased from 1.02 seconds in the 1st phase to 1.24 seconds in the 2nd phase. Traffic condition
was also significant (p = 0.000). Average headway was 1.22 seconds in light traffic and 1.04
seconds when traffic was heavy indicating that subjects tended to follow closely in heavy traffic.
The effects of the advisory message, type of sign and the interaction between them were assessed
through ANOVA on the 2nd phase results. The type of sign affected subjects’ vehicle headway in
a significant way with a p-value equal to 0.000, while the advisory message was not a significant
factor (p = 0.440) and neither was their interaction (p = 0.090). Compared to static signs,
advisory messages posted on overhead DMSs were found to be more effective in increasing
vehicle headway (0.21 seconds more). The advisory message “Keep a Safe Following Distance”
or “Keep Minimum 2 Seconds Apart” did not make a noticeable difference in vehicle headways.
Subjects participated in the 3rd phase were shown an educational video prior to the driving
simulation to educate them how to gauge their following distance per the 2-second rule.
Compared to the results obtained from the 2nd phase, the vehicle headway was significantly
increased (p = 0.000) in the 3rd phase by 0.84 seconds. Subjects were able to maintain a safe
following distance after viewing the educational video. Traffic condition still affected vehicle
headway in a significant way (p = 0.000). Average headway was 1.75 seconds in light traffic and
1.56 seconds when traffic was heavy, still considered tailgating though.
Twelve subjects partook the field study conducted mostly during the non-rush hours (between 10
AM and 4 PM.) Through a frame-by-frame analysis on the recorded videos, it found that the
average vehicle headway was 1.83 seconds. Despite the subject’s efforts to maintain a 2-second
vehicle headway, it was observed that other drivers often cut in and thus reduced headways. The
findings indicated that maintaining a safe following distance in real driving was difficult without
an effective tailgating treatment system in place. The advisory sign proposed in this study could
be a good candidate to be included in a more sophisticated tailgating treatment system.
CONCLUSIONS
A human factors study was carried out to assess drivers’ tailgating behavior and responses to
various counter-tailgating measures. Both the survey and the simulation study identified serious
tailgating issue and indicated a need for counter-tailgating measures on urban highways. The use
of advisory signs and an educational video as counter-tailgating measures to advise drivers to
maintain a safe following distance was studied via driving simulation. The findings provided
PROCEEDINGS of the Sixth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design
589
promising evidence that tailgating could be mitigated by employing the proposed counter-
tailgating measures. Most subjects were able to maintain a 2-second vehicle headway in the
simulation after viewing the educational video. It was, however, difficult for them to do so in
real driving. It is recommended that a more sophisticated tailgating treatment system containing
the proposed advisory signs be considered for urban Rhode Island highways. The effect of the
system could be augmented with education. It is hoped that this study could help lead the way in
developing effective tailgating treatment systems for US urban highways and encourage more
research in this area.
ACKNOWLEDGEMENTS
The authors would like to acknowledge the Rhode Island Department of Transportation (RIDOT)
and the University of Rhode Island Transportation Center (URITC) for their support and
guidance on this research project.
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Autonomous vehicles are gaining increased attention but surveys have shown that a large percentage of people are wary of adopting the new technology. One possible explanation for the hesitancy is the occupant would not be comfortable with the driving style as a result of the control models and their parameters as set by the manufacture. Comfort level is subjective in nature and therefore varies between individuals. To combat this issue, autonomous vehicles must be able to adapt to the driving style preference of the user. If we assume drivers are more comfortable with their own driving style, we can choose to have the vehicle learn and incorporate the driver's style into the control models. However, there is still no widely accepted “best” model. One model may prove to better represent a particular driver than other models though a driver may choose unsafe driving conditions, the replication of which should not take precedence over the safety of the occupant. In this paper we propose a multi-model approach to find the best driver model for describing an individual's longitudinal driving style on highway. A method for extracting the indicators of an individual's driving style is proposed first. Then a multi-model based evaluation method is described in detail. Chandler, Herman, & Montroll (CHM), General Motors Nonlinear (GM), Tampere (TMP), Addison & Low (AL), Optimal Velocity Model (OVM) and Neural Network (NN) models are trained and compared in this paper. The model with the best performance in replicating driving style is further coupled with model predictive controller (MPC) to include safety constraints for safer driving. Finally, the proposed multi-model approach is tested with driving data collected from 5 different drivers. The test results show that our multi-model based approach is showing advantage over single model approach in imitating an individual's longitudinal driving style.
Article
This paper seeks to assess the effectiveness of high-visibility enforcement (HVE) programs in terms of reducing aggressive driving behavior. Using Strategic Highway Research Program 2 (SHRP2) Naturalistic driving study (NDS) data, behavioral reactions of drivers before, during, and after the conduct of high-visibility enforcement programs are analyzed, in order to identify the potential effect of high-visibility enforcement in driving behavior. In this context, two fundamental aspects of aggressive driving behavior (speeding and tailgating) are employed and analyzed. To simultaneously explore the intensity and the duration of these behavioral patterns, novel metrics are defined and used in the analysis. To investigate the effect of high-visibility enforcement programs, and at the same time, to control for the effect of driver-, trip-, vehicle-, and weather-specific characteristics on the extent of speeding and tailgating, univariate grouped random parameters linear regression models are estimated. In addition, likelihoods of speeding and tailgating occurrences are analyzed simultaneously, within a grouped random parameters bivariate probit modeling framework. The results of this preliminary analysis show that even though the implementation of the high-visibility enforcement has mixed effects on the extent and the likelihood of the driving behavior metrics, it demonstrates a promising potential in modifying driving behavior.
Conference Paper
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The tailgating is a common phenomenon where aggressive drivers attempt to drive very closely to vehicles ahead pushing the leading vehicle's driver to get out of the way. Tailgating drivers are usually overestimating their skills with the belief that they can avoid rear-end collisions. The primary objective of this paper is to investigate the tailgating behavior and time headway characteristics in UAE. It also aims to provide a better understanding of the characteristics of at-fault drivers involved in tailgating-related crashes and to further identify the significant factors that affect the occurrence of such crashes. Two datasets were used in the analysis. The first is the time headway data collected from a total of 291 locations covering freeways and urban areas. A slightly more than 185,000,000 records have been analyzed to test the percentages of drivers with 1 and 2 seconds or less time headway. The second dataset include a total of 12,611 severe traffic crashes that occurred in UAE between 2010 and 2015. The findings indicated that an average of 7.1 % and 13.6 % of vehicles had a headway less than or equal to one and two second, respectively. In addition, a binary logistic regression model was developed to determine the significant factors affecting the occurrence of tailgating crashes. The model resulted in a set of significant factors including drivers’ factors (i.e., gender and nationality), vehicle factor (i.e., vehicle type), road and environment factors (i.e., road type, number of lanes and road surface condition).
Article
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human factors study was conducted to investigate the tailgating issue in Rhode Island and possible means for tailgating treatment. Tailgating is an aggressive driving behavior with a deadly consequence. Following a vehicle too close, i.e., with less than two seconds of following distance, is considered tailgating on Rhode Island highways. To mitigate rear-end collisions caused by tailgating, this study aimed to find out causes of tailgating and public's opinions on tailgating issue as well as to identify possible tailgating treatments. Consisting of a vehicle headway analysis and a questionnaire survey, this study first assessed the tailgating situation on major Rhode Island highways. Surveillance videos capturing 8-lane traffic on three test sites of I-95, I-195, and I-295 in Rhode Island were taken during both rush hours and non-rush hours each day in a two-week period during December 2008. Based on the time stamp embedded in videos, vehicle headways were collected by calculating the intervals between two consecutive vehicles on the same lane passing a fixed reference point. Vehicle headways were tabulated in increments of seconds by day of the week, time of the day, and test site. The results identified serious tailgating situation on Rhode Island highways. More than 60% of vehicles were following with less than 2 seconds of headways during rush hours while 38% were tailgating during non-rush hours. It further found that vehicles on the high speed (innermost) lane exhibited the worst tailgating behavior, especially during rush hours. With serious tailgating issue confirmed, a two-phase questionnaire survey was developed to help find the causes of tailgating and to identify drivers' responses to proposed tailgating treatments. The first phase was designed to identify the causes and effects of tailgating, and to gain insights about drivers' understanding and interpretation of tailgating behavior. Nineteen questions presented in PowerPoint slides were shown to 210 subjects participated in this phase to capture their perceptions on various tailgating issues. The second phase was developed to gather drivers' preferences regarding several proposed tailgating treatment systems. These systems, consisting of pavement marking, roadside marking, dynamic message sign, and fixed road sign were presented to 142 subjects in simulated driving videos in six questions. The questions were presented in a sequential manner and the choices shown in a question would depend on the answer chosen in the previous question. Survey results obtained from the first phase found that the majority of drivers did not know what the proper vehicle headway was to keep while following other vehicles on highways. Most of them considered tailgating a serious offense and one of the top three major causes of highway crashes, however, most of them still maintained insufficient vehicle headways while driving on highways. This finding further confirmed the observations made in the vehicle headway analysis, that is, most drivers on Rhode Island highways maintained insufficient vehicle headways. From the second phase of the survey, it found that the majority preferred horizontal bars painted on pavement as a means to help maintain safe following distance. Drivers would be advised to keep two bars visible from the vehicle ahead. Coupled with the pavement marking, most of them preferred to have the overhead graphic-aided dynamic message signs as a way to communicate to drivers about safe following distance. Based on the results of this study, recommendations to Rhode Island traffic management authorities were made. The findings of this study could contribute to the development of a standard tailgating treatment system to be included in MUTCD and help facilitate a more efficient and safer driving on US highway. © (2010) by the Transportation Research Forum All rights reserved.
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The California Highway Patrol in San Diego County receives cellular telephone calls reporting unsafe driving. The content of the calls varies, with drivers complaining about speeding cars driving over 161 km/h (100 mph) and other drivers weaving and cutting off or tailgating. In some cases, the driving conditions were even more volatile with drivers describing harassment, assaults with a weapon, or running other vehicles off the road. There were about 1,987 reported incidents from the freeways of San Diego for the months of April, June, and September 1998. The information received by the dispatchers was tabulated and put into five different categories. Analyses indicated that 24.6 percent of the calls were for "Aggressive Driving 1" (speeding plus some other behavior, such as unsafe lane changes or passing); "Aggressive Driving 2" (weaving and cutting) was reported most frequently (27.1 percent of all calls); about 12.5 percent of the calls were for "Aggressive Driving 3" (tailgating); "Speeding Alone" calls comprised 19.8 percent of the total; and the rest were for "Road Rage" (16.1 percent). Of the 1,987 calls, 33 percent were generated on Interstate 5, the busiest and longest in the county, followed by Interstate 15, which accounted for 22 percent of the calls. The high number of calls can be attributed to the high average daily traffic volumes at each interchange and the longer interstate lengths. Similarly, Interstate 8 seemed to have a lower number of calls than expected, because the urban portion of the freeway is not as long and the remaining distance had fewer vehicles at each interchange. This was further corroborated and both volume and length were robustly correlated with the number of phone reports per freeway. Additionally, chi-squares tests indicated that the time of the day and day of the week influenced the type and number of calls received.
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Three on-road studies were conducted to determine how headway maintenance and collision warning displays influence driver behavior. Visual perspective, visual perspective with a pointer, visual perspective combined with an auditory warning, discrete visual warning, and discrete auditory warning were assessed during both coupled headway and deceleration events. Results indicate that when drivers are provided with salient visual information regarding safe headways, they utilize the information and increase their headway when appropriate. Auditory warnings were less effective than visual warnings for increasing headways but may be helpful for improving reaction time during events that require deceleration. Drivers were somewhat insensitive to false alarm rates, at least during short-term use. Finally, and most important, driver headway maintenance increased by as much as 0.5 s when the appropriate visual display was used. However, a study to investigate the longterm effects of such displays on behavior is strongly recommended prior to mass marketing of headway maintenance/collision warning devices.
Article
In an attempt to achieve an improvement in drivers' following behavior, markings were devised and used in France which comprised arrow shapes, or Chevrons, laid on the road surface at regular intervals. Drivers should leave two Chevrons between the front of their vehicle and the rear of the vehicle they are following, to maintain a reasonably safe following distance. Trials of these markings have been undertaken in the United Kingdom on the M1 motorway in Leicestershire and Northamptonshire, where traffic flows were higher.
Article
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.
Article
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.
Conference Paper
Postans and Wilson (1983) observed that on the Bedfordshire stretch of the M1 motorway the most frequent cause of personal road accident injuries between 1976-1979 was the rear-end shunt. Tailgating is cited as the primary contributory factor in rear-end shunts. It has been proposed that larger headways will reduce the number of road accident injuries incurred and commonly recommended that a time headway (TH) of 2 seconds is employed. Other studies have shown that this recommendation is frequently ignored. The work described involved a controlled experimental study to (a) determine the effects of providing continuous time headway feedback on driving behaviour and (b) evaluate the actual interface employed. The findings of the study suggest that while the use of a TH feedback system may decrease the TH adopted by a driver, these behavioural changes are likely to be a reaction to the system implemented, and not so much a general adoption of increased THs. Results suggest that a system as described above may be generally accepted by drivers, but the implications of the likely cost of the system are unclear. In terms of reducing adopted time headways, its practical value may be limited in traffic conditions where focused attention occurs or a degree of social pressure is imposed upon the driver. As a learning device, these initial findings indicate that such a system may not be particularly effective
Tailgating. Safety Centre for Automotive Safety Research
  • P T Hutchinson
Hutchinson, P.T. (2008). Tailgating. Safety Centre for Automotive Safety Research, University of Adelaide, Australia, Research Report # CASR046.
Minnesota Tailgating Pilot Project Estimate of motor vehicle traffic crashes by year, manner of collision and crash severity
  • Dot Minnesota
Minnesota DOT. (2006). Minnesota Tailgating Pilot Project, Report and Summary, http://www.dot.state.mn.us/trafficeng/tailgating/index.html. Accessed March 5, 2008. National Center for Statistics and Analysis. (2010). Estimate of motor vehicle traffic crashes by year, manner of collision and crash severity, GES 2006-2008. CATS 2010.00454.
Saving lives: RSF recognizes nine outstanding highway safety projects
Roadway Safety Foundation. (2001). Saving lives: RSF recognizes nine outstanding highway safety projects. Road Safety Reporter.