Feedback interventions and driving speed: A parametric and comparative analysis

Five experiments were conducted to assess the effects of several variables on the efficacy of feedback in reducing driving speed. Experiment 1 systematically varied the criterion used to define speeding, and results showed that the use of a lenient criterion (20 km/hr over the speed limit), which allowed for the posting of high percentages of drivers not speeding, was more effective in reducing speeding than the use of a stringent criterion (10 km/hr over the speed limit). In Experiment 2 an analysis revealed that posting feedback reduced speeding on a limited access highway and the effects persisted to some degree up to 6 km. Experiments 3 and 4 compared the effectiveness of an unmanned parked police vehicle (Experiment 3) and a police air patrol speeding program (Experiment 4) with the feedback sign and determined whether the presence of either of these enforcement variables could potentiate the efficacy of the sign. The results of both experiments demonstrated that although the two enforcement programs initially produced larger effects than the feedback sign, the magnitude of their effect attenuated over time. Experiment 5 compared the effectiveness of a traditional enforcement program with a warning program which included handing out a flier providing feedback on the number and types of accidents occuring on the road during the past year. This experiment demonstrated that the warning program produced a marked reduction in speeding and the traditional enforcement program did not. Furthermore, the warning program and a feedback sign together produced an even greater reduction in speeding than either alone.     

An analysis of public posting in reducing speeding behavior on an urban highway

The effects of public posting on speeding behavior on an urban highway were assessed using a reversal design. During baseline the percentage of drivers speeding was measured with a concealed radar unit. During the daily posting condition a highway sign was installed which provided feedback on the percentage of drivers not speeding yesterday and the best record to date. This sign was then covered and reintroduced. Results indicated that the sign was effective in reducing speeding behavior. Furthermore, the effects were most pronounced in reducing the speeds of the faster drivers. Next, daily and weekly postings were compared with the sign alone without numerical feedback: results revealed that the weekly posting condition was as effective as the daily posting condition, but that the sign had no influence when numbers were not posted. Finally, the weekly posting procedure remained effective during a 6-month follow-up condition.     

A comparison of the effects of posted feedback and increased police surveillance on highway speeding

A counterbalanced, reversal design was used to compare the effectiveness of posted feedback and increased police surveillance in reducing speeding on two urban highways. Drivers' speeds were measured using a concealed radar unit. During public posting, a large highway sign, which listed the percentage of drivers not speeding during the preceding week and the best record to date, was erected on each street. Use of the feedback sign alternated with periods of baseline and periods of increased police surveillance and ticketing. During increased police surveillance, highly visible, stationary police radar patrols were established along the highways for either 30 min or 60 min per day, 5 days per week. Results indicated that although public posting was highly effective in reducing the percentage of speeding drivers, increased police surveillance was not. Thus, since the feedback sign required only 30 min per week to maintain, public posting was at least 10 times more efficient in controlling speeding than was police surveillance and ticketing.     

A replication of the use of public posting in traffic speed control

In an attempt to replicate several previous studies, a reversal design was used to assess the effects of publicly posted feedback on vehicle speed reduction. The intervention phases consisted of daily posted feedback that supplied drivers with either accurate or inaccurate information regarding the percentage of vehicles exceeding the speed limit on the road. Results from the two feedback conditions indicated no speed reduction in comparison to baseline levels. These results are discussed in light of previous studies that found strong effects for such feedback. Baseline levels of driver compliance and methodological differences may limit the effectiveness of posted feedback in reducing speeding.     

Effects of speed feedback signs and law enforcement on driver speed

This study analyzes the effects of implementing three speed management strategies, namely speed feedback signs, periodic law enforcement, and speed feedback sign supported with periodic law enforcement on driver speed behavior and compliance. To analyze the effectiveness of each strategy, nine locations in Pima County, Arizona, were studied in a cross-sectional framework. For each study site, the driver’s speed, date, time, and vehicle’s length were collected at a location prior to the speed management zone as the baseline, at the speed management zone, and downstream of the speed management zone. The general effect showed that all the strategies were effective in reducing average speed and the proportion of drivers exceeding the speed limit. In addition, the results of the robust heteroscedastic ANOVA test showed that among all the strategies, the speed feedback sign supported with periodic law enforcement was the most effective one. Moreover, it was shown that by supporting the speed feedback sign with periodic law enforcement, the reduction in average speed and proportion of drivers exceeding the speed limit would last, even after passing the speed management strategy. In other words, the existence of periodic law enforcement could potentially modify drivers’ behaviors and increase the spatial effectiveness of speed feedback signs. Comparing the behavior of truck and passenger car drivers also revealed similar results. That is, both truck and passenger car drivers tend to slow down after observing the speed management strategy. The experimental evidence indicates positive benefits for reducing excessive speeding behaviors at the sites.     

On-road study investigating the mode of feedback delivery on young drivers’ speed management

Feedback has been shown to be instrumental in learning. Refining how it is delivered in driver training has the potential to reduce crash risk. Therefore, the aim of the present study was to examine the effect of the medium in which feedback is delivered (verbal, written, graphical) on young drivers’ speed management behaviour. Sixty young drivers, randomly allocated to one of four feedback groups (i.e., Control, Verbal feedback, Written feedback, and Graphical feedback) completed one training and two test drives using an instrumented vehicle on-road. After the first (baseline) drive, participants were provided feedback about the number of times they exceeded the speed limit, their maximum speed, as well as the financial penalties associated with such driving behaviour, and safety implications. The content of feedback remained the same for all training groups, except for the manner in which the feedback was presented. Verbal feedback was provided verbally by the researcher; written feedback on paper; and graphical feedback using a series of graphs on a computer screen. Control received no such intervention. Two test drives followed, one immediate post-training, and the second one week post-training. Feedback, irrespective of medium improved young drivers’ speed management. Verbal and graphical feedback yielded the greatest reduction in speeding behaviour, with graphical feedback having the most impact in the two speed zones under examination (50 km/h & 80 km/h). Control showed the poorest speed management behaviour in all drives. These findings have important implications for the development of a new approach to improve young drivers’ speed management behaviour.     

The effects of a rectangular rapid-flashing beacon on vehicle speed

In 2008, nearly 31% of vehicle fatalities were related to failure to adhere to safe vehicle speeds (National Highway Traffic Safety Administration [NHTSA], 2009). The current study evaluated the effect of a rectangular rapid-flashing beacon (RRFB) triggered by excessive speed on vehicle speed using a combined alternating treatments and reversal design. The percentage of vehicles traveling above 41 mph (66 km per hour) decreased by 20%, and speed distributions showed a shift toward lower speeds during the RRFB condition.     

The role of drivers’ social interactions in their driving behavior: Empirical evidence and implications for car-following and traffic flow

Models for describing the microscopic driving behavior rarely consider the “social effects” on drivers’ driving decisions. However, social effect can be generated due to interactions with surrounding vehicles and affect drivers’ driving behavior, e.g., the interactions result in imitating the behavior of peer drivers. Therefore, social environment and peer influence can impact the drivers’ instantaneous behavior and shift the individuals’ driving state. This study aims to explore empirical evidence for existence of a social effect, i.e., when a fast-moving vehicle passes a subject vehicle, does the driver mimic the behavior of passing vehicle? High-resolution Basic Safety Message data set (N = 151,380,578) from the Safety Pilot Model Deployment program in Ann Arbor, Michigan, is used to explore the issue. The data relates to positions, speeds, and accelerations of 63 host vehicles traveling in connected vehicles with detailed information on surrounding environment at a frequency of 10 Hz. Rigorous random parameter logit models are estimated to capture the heterogeneity among the observations and to explore if the correlates of social effect can vary both positively and negatively. Results show that subject drivers do mimic the behavior of passing vehicles –in 16 percent of passing events (N = 18,099 total passings occurred in freeways), subject vehicle drivers are observed to follow the passing vehicles accelerating. We found that only 1.2 percent of drivers normally sped up (10 km/hr in 10 s) during their trips, when they were not passed by other vehicles. However, if passed by a high speed vehicle the percentage of drivers who sped up is 16.0 percent. The speed change of at least 10 km/hr within 10 s duration is considered as accelerating threshold. Furthermore, the acceleration of subject vehicle is more likely if the speed of subject driver is higher and more surrounding vehicles are present. Interestingly, if the difference with passing vehicle speed is high, the likelihood of subject driver’s acceleration is lower, consistent with expectation that if such differences are too high, the subject driver may be minimally affected. The study provides new evidence that drivers’ social interactions can change traffic flow and implications of the study results are discussed.     

Speed choice in relation to speed limit and influences from other drivers

Speeding is a general problem in traffic and exploring factors underlying the choice of speed is an important task. In the present paper, based on data from Swedish drivers on 90 km/h roads, drivers’ attitudes towards speeding and influences from other road users on the drivers’ speed choice were investigated. Unobtrusively recorded vehicle speeds were compared with drivers’ responses to questions concerning their speed choice (N=533). The present investigation replicates a previous study on 50 km/h roads, where a model including measures of attitudes and perceptions about others’ behaviour could explain about 15% of observed behaviour. In the present study, where a majority of the drivers observed exceeded the speed limit, a similar model could explain 41% of the variance in observed speed. Theoretical and practical implications of the results are discussed.     

Improving young drivers’ speed management behaviour through feedback: A cognitive training intervention

The aim of the present study was to examine which aspect of content-based feedback about drivers’ speed management behaviour (performance, financial infringements and safety implications for speeding) yielded positive changes in compliance with the speed limit. One hundred young drivers were randomly allocated to one of five groups (Control, Performance Feedback, Performance and Finance Feedback, Performance and Safety Feedback, Combined Feedback). Depending on group randomly allocated to, participants completed a baseline drive and received feedback about their speed management (except control). Immediately after, all groups completed a post-training drive, followed by a second drive one week later. A reduced sample (25 per cent dropout) completed a third test drive six month post-training. All drives were completed in a computer-based driving simulator. Feedback pertaining to their speed management behaviour was provided verbally immediately after the baseline drive by the researcher. Performance Feedback group received feedback about own speed-related performance (e.g., mean speed, time violated during the drive); Performance and Finance Feedback group received feedback about own performance and potential fines that could be received for exceeding the speed limit; Performance and Safety Feedback group received feedback about own performance and potential safety outcomes for them and other passengers; the Combined Feedback group received feedback about own performance, financial infringements and safety implications for speeding; and the Control group received no feedback. The results showed that all types of feedback are effective in modifying young drivers’ speed management behaviour, and these effects were present up to six months post-training in both low and high-speed zones. These findings have valuable implications in the development of a new training approach to improve young drivers’ speed management behaviour.     

Do internals speed less and externals speed more to cope with the death anxiety?

Past research has showed that mortality salience (MS) increases reckless driving and speeding when the individual perceives driving to be relevant to his or her self-esteem. We claimed that drivers’ control orientations also play a significant role in the relationship between MS and speeding. We hypothesized that both a general desirability of control and traffic locus of control (T-LOC) would moderate the effect of MS on speeding. We tested our hypothesis using an online experiment on a sample of 208 young male drivers. Participants were exposed to either mortality or dental pain salience, and they filled out desirability of control, T-LOC, and self-report speeding measures. The results showed that, for individuals with low desirability of control, MS increased preferred speed and decreased intention to comply with speed limit and the percentage of time complied with the speed limit on urban roads with 50 km/h speed limit. For individuals with high desirability of control, on the other hand, MS increased intention to comply with the speed limit on rural roads and percentage of the time complied with the speed limit on both urban and rural roads. In contrast, the interaction between MS and T-LOC showed that an external T-LOC is positively associated with both intention to comply and the percentage of the time complied with the speed limits only on rural roads with 90 km/h.     

Decreasing driver speeding with feedback and a token economy

On-road research suggests that driver feedback combined with a token economy (a system of delayed reinforcement whereby tokens or points are distributed following a desired behaviour and are later exchanged for desired items) can reduce speeding, and that an incentive system without feedback may be sufficient to achieve this reduction. In two studies, we investigated the necessary and sufficient conditions required for this intervention to reduce speeding, and the efficacy of conducting such research using a driving simulator. Study 1 served to validate the simulator procedure. Participants completed a simulated drive while receiving feedback on their speed and a speed-based token economy. The intervention decreased their speeding compared with that of a control group. Study 2 investigated the amount of speed reduction that could be achieved with just one intervention component (i.e., feedback alone or a token economy alone) compared with feedback and a token economy combined or a control condition. Participants completed a 30-min simulated drive. Overall, drivers who received feedback combined with a token economy spent the least amount of time driving above the speed limit, had the slowest mean speed, and had the smallest standard deviation of speed. Drivers exposed to a token economy alone showed similar speed reductions. However, drivers exposed to feedback alone drove at speeds similar to control participants. Replicating these results under more realistic operating conditions could inform policy-makers and car manufacturers. Furthermore, the simulator proved a cost-effective and efficient means for examining the intervention.     

THE FAILURE OF FEEDBACK ON ALCOHOL IMPAIRMENT TO REDUCE IMPAIRED DRIVING

We examined the effects of rules to govern drinking, individual feedback on blood alcohol concentration (BAC), and public posting of group data on impaired driving on the incidence of impaired driving. Level of impairment was determined from breath samples taken from tavern patrons. Following baseline, an intervention package consisting of (a) cards to guide patrons in pacing their drinking to stay under the legal limit, (b) individual feedback on BAC, and (c) posted group feedback on the percentage of patrons driving while impaired the preceding week was introduced in two taverns. Results indicated that the intervention package did not reduce the percentage of impaired drivers departing either tavern. The addition of a brief intensive police enforcement program directed at impaired driving produced a short-term reduction in impaired driving.     

Exploration of older drivers’ speeding behaviour

Speeding increases crash risk and resulting injury severity. Older drivers are at increased risk of injury due to frailty, at increased risk of crashing due to slower reaction times, and have less agility judging time and distance compared to younger drivers. However, there is little objective evidence about older drivers’ speeding behaviour. Cross-sectional data from older drivers living in the suburban outskirts of Sydney, Australia, were used to determine the proportion of drivers involved in speed events, and examine factors that may influence this behaviour. Driving speed was estimated in approximately one-second intervals using Global Positioning System (GPS) location. Speed events were defined as driving 1 km/h or more, with 3% tolerance, above a single speed limit, averaged over 30-s of travel. Driving data from one-week were recorded for 344 participants aged 75–94 years (median 80). The majority of participants (78%) were involved in a speed event. Speed events per participant ranged from zero to 186 (median 8). Younger participants, those living in rural areas, and those driving on familiar roads closer to home were more likely to be involved in speed events adjusted for distance driven. In addition, rural residents were more likely to be involved in speed events when they had not been a driver involved in a crash during the previous year compared to those involved in a crash. Measures of visual and cognitive function did not predict involvement with speed events per distance (p > 0.2). These findings are important for policy-makers and researchers addressing older drivers’ speeding to reduce the incidence of crashes and resulting fatalities and injuries. As no evidence was found for speeding being associated with functional decline, countermeasures to address speeding for other drivers seem likely to be relevant to older drivers.     

Analysis of rainfall impacts on platooned vehicle spacing and speed

This paper investigates the impact of rainfall on the behavior of drivers in a car-following state by analyzing the differences in time gap, speed, and following distance of platooned vehicles between no-rain and rainy weather conditions on a two-lane rural state highway. Time gap, following distance, and individual vehicle speed were observed. Platooned vehicles were identified by a maximum time gap threshold of 4 s, allowing for interactions between vehicles beyond perception–reaction time. Rainfall intensity was utilized as the measure of local precipitation conditions and was categorized according to American Meteorological Society standards. The analysis showed that rainy weather conditions were strongly correlated with greater spread in speed distributions when compared to dry conditions. Further, the shift from no-rain to rain showed an increase in time gap and a reduction in speed. No statistically significant differences were observed between following distances in any weather conditions – suggesting that drivers tend to maintain following distance irrespective of weather conditions and speed reduction causes the observed time gap increase. This is supported by the observed 5.6% decrease in mean time gap – from 1.97 s to 2.1 s and the 3.7% decrease in mean speed – from 47 mph (75.6 km/h) to 45.3 mph (72.9 km/h).     

Increasing motorist compliance and caution at stop signs.

This study evaluated strategies to improve motorist compliance and caution at three stop‐sign‐controlled intersections with a history of motor vehicle crashes. The primary intervention was a light‐emitting diode (LED) sign that featured animated eyes scanning left and right to prompt drivers to look left and right for approaching traffic. Data were scored from videotape on the percentage of drivers coming to a complete stop and the percentage of drivers looking right before entering the intersection. Observational data were collected on the percentage of right‐angle conflicts (defined as braking suddenly or swerving from the path to avoid an intersection crash). The introduction of the LED sign according to a multiple baseline across the three intersections was associated with an increase in the percentage of vehicles coming to a complete stop at all three intersections and a small increase in the percentage of drivers looking right before entering the intersections. Conflicts between vehicles on the major and minor road were also reduced following the introduction of the animated eyes prompt.     

Factors predicting intentions to speed in a work and personal vehicle

The available evidence suggests that people who drive for work purposes engage in less safe driving practices than other drivers. The study examined this issue by surveying 204 people who drive for work purposes, in four different vehicle fleets. It was predicted that work-related drivers would report more speeding and a higher intention to speed in a work vehicle than their personal vehicle. Additionally, the constructs within the Theory of Planned Behaviour, along with anticipated regret, were used to explore factors contributing to speeding in the two settings. Contrary to prediction, the participants reported less speeding and a lower intention to speed in a work vehicle than their personal vehicle. Further analysis revealed that the intentions of drivers in the two settings were significantly different in relation to anticipated regret and subjective norms. Thus, it would appear that these two psychological mechanisms may work to discourage speeding behaviour in the work context. However, these findings need to be replicated with a larger sample of drivers from more diverse vehicle fleets.     

Road signs depicting childrens's book illustrations temporarily reduce speed on urban roads

Speeding on urban roads is a major road safety problem. Police enforcement and speed humps are effective measures to prevent drivers from speeding. However, these measures may also elicit none compliance because of their restrictive nature. Therefore, non-compulsive measures that nudge drivers to adopt low speeds are also required. One such a nudge was evaluated: road signs displaying children’s book illustrations. These signs display illustrations which were created by the late illustrator and writer of books for toddlers, Dick Bruna, and are named ‘Dick Bruna signs’. The idea of the developers of these signs was that they will evoke feelings of caution and care in drivers and this will make them drive slower. To evaluate the effect, two studies were conducted. In the first study participants watched photos from the driver’s perspective. They had to report how fast they expected others would drive and how fast they themselves would drive. Participants reported speeds of others higher than their own speeds but the pattern was the same: speeds on photos with a Dick Bruna sign were approximately 4 km/h lower than on the same photos without a Dick Bruna sign and speeds were not significantly lower when a neutral sign such as an advertisement was visible. In the second study speeds were measured during seven consecutive weeks on five experimental roads and five comparison roads. On the experimental roads, during the week 3–5 a Dick Bruna sign was placed. Controlled for developments in speed on the comparison roads in the same period, mean speed was marginally significant lower, and the V85 speed and the proportion of speed offenders were significantly lower in only the first week after placement of the signs.     

A naturalistic study of the impact of message framing on highway speeding

Speeding is the most common road violation, and is one of the main causes of crashes. To protect road users, authorities use sanctions and preventive measures to prompt drivers to observe speed limits. However, the efficacy of prevention messages varies according to a number of factors, among which risk framing is important. We ran a study to test whether gain is more effective than loss (framing effect). Four anti-speeding messages were presented on variable-message signs, along one side of a busy 8-lane highway in France (speed limit: 130 km/h – 80 mph), during 6 weekends. Within a between subject design, the messages differed in orientation (gain vs. loss vs. no message) and theme (crash vs. fuel consumption). The drivers’ speed was recorded on the highway 2 km (1.25 miles) after the sign (6486 recordings of speed). The results showed that speed was lower when a message was displayed than in the control condition, and when the message was gain-framed rather than loss-framed. These effects were stronger on the left lanes (overtaking lanes). Hence, gain framed messages are recommended for prevention campaigns at least when no risk factor is salient.     

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

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