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Speeding in urban environments: Are the time savings worth the risk?

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... Why have a computer perform these tasks instead of the driver? Consider the case of the driver who understands that "time-saving opportunities," such as highway lane changes, seldom yield anything other than additional risk for everyone (Ellison & Greaves, 2015). Yet that driver still can't help responding to an opportunity to pass another car or to an aggressive move made by another driver. ...
Article
Each year, millions of automobile crashes occur when drivers fail to notice and respond to conflicts with other vehicles, bicyclists, and pedestrians. Today, manufacturers race to deploy automation technologies to help eliminate these mishaps. To date, little effort has been made to educate drivers about how these systems work or how they affect driver behavior. Driver education for automated systems amounts to additional pages in an owner’s manual that is known to be a seldom-used glove box reference. In this article, we review the history of automation deployed in the airline cockpit decades ago. We describe how automation helped avoid many common crash scenarios but at the same time gave rise to new kinds of crashes. It was only following a concerted effort to educate pilots about the automation, about themselves, and about the concept of a human-automation team that we reached the near-zero crash rate we enjoy today. Drawing parallels between the automation systems, the available pilot and driver research, and operational experience in both airplanes and automobiles, we outline knowledge standards for drivers of partially automated cars and argue that the safe operation of these vehicles will be enhanced by drivers’ incorporation of this knowledge in their everyday travels.
... La evidencia refuta este temor, aunque sea contraintuitivo. Un seguimiento con GPS a automovilistas en Sydney, Australia, mostró que aquellos que conducían a exceso de velocidad en zonas donde el límite era 50 km/h, ahorraban solo entre 1 y 2 % en su tiempo de viaje total, en el orden de segundos (Ellison and Greaves, 2015). Esto se explica porque en ciudad los tiempos están condicionados por el flujo de los demás vehículos y por las intersecciones, que hacen que los conductores se pasen mucho tiempo detenidos, acelerando y frenando, en lugar de conduciendo a velocidades cercanas al límite. ...
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Chile es un país inseguro para transitar en sus calles, avenidas, caminos y carreteras. En nuestro país al año se producen cerca de 12 muertes en siniestros de tránsito por cada 100.000 habitantes, un valor muy superior al de los países con mejores prácticas en seguridad vial, según datos compilados por la Organización para la Cooperación y el Desarrollo Económicos (OCDE), según se aprecia en la Figura 1. La cifra de muertos por siniestros de tránsito en Chile aproximadamente triplica al número de muertes por homicidios . Sin embargo, los siniestros de tránsito y sus consecuencias reciben menos atención y han sido de alguna forma "naturalizados" en el imaginario colectivo. Con todo, debería ser prioridad para el país abordar de forma contundente el tema de la seguridad vial, por todos los costos sociales y de salud pública que tienen los siniestros de tránsito y porque en Chile hay un amplio margen de acciones de mejora. Una de estas acciones es la reducción y fiscalización de la velocidad máxima en áreas urbanas. El objetivo de este documento es proveer los argumentos técnicos en que se basa la petición de establecer que el límite de velocidad en las ciudades chilenas sea 50 km/h, en lugar del límite actual de 60 km/h.
... La velocidad es uno de los comportamientos de riesgo más comunes tanto en la producción de accidentes de tráfi co como en la gravedad de sus consecuencias ya sea de manera general (Ellison & Greaves, 2015;Elvik, Christensen, & Amundsen, 2004) como de manera específi ca en la accidentalidad de vehículos de dos ruedas (Lardelli-Claret, Jimenez-Moleon, Luna-del-Castillo, García-Martín, Bueno-Cavanillas, & Gálvez-Vargas, 2005;Steg & Brussel, 2009). ...
Article
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Motorcycle accidents are one of the most important road safety issues worldwide. There is a lack of specific researches about the characteristics of the scooter-motorcycle accidents, motivated by the absence not only of a precise definition and but also by a properly identification of the different type of two-wheeled vehicles within the accident´s database. The aim of this study is to determine the characteristics of the 293 scooter-motorcycle drivers deceased in Spain in the period 2006 to 2011. According to the nature of the variables involved were performed descriptive and association analysis. The results of the analysis enable the identification some of the main human factors associated with the fatal accidents of scooter-motorcycle drivers.
... Speeding is one of the most common driving behaviors and is also considered one of the largest contributors to road injuries and fatalities [1][2][3]. The recent statistics from the Chinese Road Traffic Statistics Yearbook has reported that a total of 8812 speeding-related traffic fatalities happened in 2011, which accounted for 14.13% of all traffic deaths [4]. ...
Speeding is a major contributing factor to traffic crashes and frequently happens in areas where there is a mutation in speed limits, such as the transition zones that connect urban areas from rural areas. The purpose of this study is to investigate the effects of an in-vehicle audio warning system and lit speed limit sign on preventing drivers' speeding behavior in transition zones. A high-fidelity driving simulator was used to establish a roadway network with the transition zone. A total of 41 participants were recruited for this experiment, and the driving speed performance data were collected from the simulator. The experimental results display that the implementation of the audio warning system could significantly reduce drivers' operating speed before they entered the urban area, while the lit speed limit sign had a minimal effect on improving the drivers' speed control performance. Without consideration of different types of speed limit signs, it is found that male drivers generally had a higher operating speed both upstream and in the transition zones and have a larger maximum deceleration for speed reduction than female drivers. Moreover, the drivers who had medium-level driving experience had the higher operating speed and were more likely to have speeding behaviors in the transition zones than those who had low-level and high-level driving experience in the transition zones.
Article
Este estudio analizó los accidentes de motocicleta y ciclomotor en Barcelona (España). 53.190 informes de conductores de motocicleta y ciclomotor involucrados en accidentes entre los años 2006 y 2011 fueron extraídos de la base de datos de accidentes con víctimas de la Dirección General de Tráfico. Estos datos fueron analizados en términos de sexo, grupos de edad, motivo del desplazamiento, día de la semana, infracciones de velocidad, uso del casco y lesividad, con el objetivo de estudiar las características de los accidentes de motocicleta y ciclomotor en Barcelona y evaluar las diferencias entre conductores varones y mujeres en estos accidentes. La gravedad de los accidentes sufridos por conductores varones es superior a la de las mujeres. Se encontraron diferencias significativas en todas las variables consideradas en el estudio, lo que implica diferencias en el perfil del conductor de accidentado.
This study analysed motorcycle crashes in Spain. Ninety-nine thousand three hundred and four motorcycle crash reports filed in the years 2006–2011 were extracted from the Directorate General of Traffic database of crashes with victims. These data were analysed in terms of gender, age groups, trip purpose, type of crash, speed violation, day of the week, harm caused, use of helmet and psychophysical conditions of the driver to study the characteristics of motorcycle crashes in Spain and to assess the differences between male and female motorcycle drivers in these crashes. Significant differences were found in all the variables considered in the study, which implies gender differences in the profile of the injured motorcycle driver. The severity of motorcycle crashes suffered by male drivers is higher than that of women. These results corroborate the need to develop measures differentiated by gender, based on their profile.
Article
Objectives: The objective of this study was to examine the safety effects of increases in U.S. state maximum speed limits during the period 1993-2013. Methods: Poisson regression was used to model state-by-state annual traffic fatality rates per mile of travel as a function of time, the unemployment rate, the percentage of the driving age population that was younger than 25, per capita alcohol consumption, and the maximum posted speed limit on any road in the state. Separate analyses were conducted for all roads, interstates and freeways, and all other roads. Results: A 5 mph increase in the maximum state speed limit was associated with an 8% increase in fatality rates on interstates and freeways and a 4% increase on other roads. In total, there were an estimated 33,000 more traffic fatalities during the years 1995-2013 than would have been expected if maximum speed limits had not increased. In 2013 alone, there were approximately 1,900 additional deaths - 500 on interstates/freeways and 1,400 on other roads. Conclusions: There is a definite trend of increased fatality risk when speed limits are raised. As roadway sections with higher speed limits have become more ubiquitous, the increase in fatality risk has extended beyond these roadways. The increase in risk has been so great that it has now largely offset the beneficial effects of some other traffic safety strategies. State policymakers should keep this trade-off in mind when considering proposals to raise speed limits.
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The Relationship Between Speed and Accidents on Rural Single-carriageway Roads
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Taylor, M.C., Baruya, A., Kennedy, J.V., 2002. The Relationship Between Speed and Accidents on Rural Single-carriageway Roads. Crowthorne, Berkshire.
The 100-Car Naturalistic Driving Study, Phase II -Results of the 100-Car Field Experiment
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Improving Road Safety in Sweden: An Analysis of the Potential for improving Safety, the Cost-Effectiveness and Cost-Benefit Ratios of Road
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Elvik, R., Amundsen, A.H., 2000. Improving Road Safety in Sweden: An Analysis of the Potential for improving Safety, the Cost-Effectiveness and Cost-Benefit Ratios of Road. Oslo, Norway.
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Speed rehabilitation: should we deliver points or education
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McKenna, F.P., 2003. Speed rehabilitation: should we deliver points or education. In: Behavioural Research in Road Safety Thirteenth Seminar. Department for Transport, pp. 221-231.
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Results of the NSW Intelligent Speed Adaptation Trial: Effects on Road Safety Attitudes, Behaviours and Speeding. Roads and Traffic Authority
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NSW Centre for Road Safety, 2010. Results of the NSW Intelligent Speed Adaptation Trial: Effects on Road Safety Attitudes, Behaviours and Speeding. Roads and Traffic Authority, Sydney, Australia.
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An empirical assessment of the feasibility of battery electric vehicles for day-to-day driving
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Greaves, S.P., Backman, H., Ellison, A.B., 2014. An empirical assessment of the feasibility of battery electric vehicles for day-to-day driving. Transp. Res. Part A: Policy Pract. 66, 226-237, http://dx.doi.org/10.1016/j.tra.2014.05.011.
Development of a GPS/Web-based prompted-recall solution for longitudinal travel surveys
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Greaves, S.P., Fifer, S.J., Ellison, R.B., Germanos, G., 2010. Development of a GPS/Web-based prompted-recall solution for longitudinal travel surveys. Transp. Res. Rec. 2183, 69-77.
Estimating the willingness to pay and value of risk reduction for car occupants in the road environment
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Speeding is a significant contributor to crash risk but is a particularly emotive issue in school zones. School zones have high levels of pedestrian activity and a relatively high proportion of children which makes it an especially important area for controlling speeding. However, most of the information we have about speeding comes from targeted police enforcement. There is little information on daytoday speeding in school zones and even less information on how speeding behaviour in school zones varies across time. This paper examines speeding behaviour in school zones in Sydney, Australia using GPS, spatial, demographic and psychological data collected from 147 drivers over five weeks. The focus is on both the duration and magnitude of speeding and how differences relate to a number of driver, trip, vehicle and road characteristics. The main findings are that 23% of the distance travelled in school zones is above the speed limit, a rate higher than on urban arterials and residential streets. Furthermore, a small minority of drivers exceeded the speed limit for as much as half the distance travelled. These results demonstrate that despite efforts at reducing speeding in school zones and more generally, the practice remains very common. It appears that changing the road environment to force drivers to slow down may be more effective than information campaigns in changing drivers' speeding behaviour.
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This paper details the development of a Global Positioning System collection solution for a longitudinal (10-week) survey of driving behavior in Sydney, Australia: the primary purpose is to investigate behavioral responses to variable rate charging regimes. The study calls for data to be transmitted regularly (wirelessly) to check the quality of data as they are being collected and provide the basis for a web-based prompted recall (PR) survey in which participants can view their trips, confirm details, and provide information on who was driving, number of passengers, and trip purpose. Following details of the technological setup, details are provided of the data processing issues involved and the development of the PR survey. Pilot testing of the approach on 30 motorists demonstrates that contrary to popular belief, highly accurate data of this nature can be collected for several weeks with little respondent burden.
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Joint household travel, with or without joint participation in an activity, constitutes a fundamental aspect in modelling activity-based travel behaviour. This paper examines joint household travel arrangements and mode choices using a utility maximising approach. An individual tour-based mode choice model is formulated contingent on the choice of joint tour patterns where joint household activities and shared ride arrangements are recognised as part of the joint household decision-making that influences the travel modes of each household member. Two models, one for weekend and one for weekday, are estimated using empirical data from the Sydney Household Travel Survey. The results show that weekend travel is characterised by a high joint household activity participation rate while weekday travel is distinguished by more intra-household shared ride arrangements. The arrangements of joint household travel are highly associated with travel purpose, social and mobility constraints and household resources. On weekends, public transport is mainly used by captive users (i.e., no-car households and students) and its share is about half of that on weekdays. Also, the value of travel time savings (VOTs) are found to be higher on weekends than on weekdays, running entirely counter to the common belief that weekend VOTs are lower than weekday VOTs. This paper highlights the importance of studying joint household travel and using different transport management measures for alleviating traffic congestion on weekdays and weekends.
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People make systematic and predictable mistakes regarding estimations of average speed and journey time. In addition, people have been shown to commit a time-saving bias by underestimating the time that can be saved when increasing from a low speed and overestimating the time that can be saved when increasing from a relatively high speed. These misestimations have been shown to relate to biases in judgments of the speed required to arrive at a specific time and to choosing unduly high speed. Professional drivers, such as taxi drivers, might be less susceptible to these biases due to their increased driving experience. In the current study, we interviewed taxi drivers about a journey they were currently making and examined their estimations of journey time, average speed and time savings. Compared to a group of non-professional car drivers, taxi drivers showed the same considerable misestimations of driving speed, journey time and time savings as non-professionals. However, overestimations of time savings among taxi drivers were smaller than those made by car drivers. We discuss the practical significance of these findings.
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Higher speeds are associated with increases in the probability of crashing and the severity of the outcome. Logically drivers speed to save time, and research evidence supports this assertion. It is therefore important to investigate drivers' understanding of how speed change impacts on journey time. Since it is likely that drivers do not appreciate the reciprocal nature of the function which links these two variables, and its implications, two predictions can be made: the impact of a speed change will be underestimated at low speeds and overestimated at high speeds. This issue was addressed through four questions generated by manipulating Speed Change (increase versus decrease) and Starting Speed (30 mph versus 60 mph) with the participants being asked how they felt these variables would impact on journey time. These were included in a large survey addressing speed-related issues. Participants were a representative quota sample of 1005 UK drivers, interviewed by questionnaire. The findings indicated that three of the four questions produced results consistent with the predictions made. Furthermore, a repeated measures factorial ANOVA indicated that there was no real appreciation of how starting speed impacted on journey time. A disordinal interaction provided evidence that drivers wrongly believed that as starting speed increased the impact of a speed rise also increased; the opposite is true. For speed decreases, drivers appeared to think that starting speed had little impact on the amount of time saved. It is recommended that these findings be integrated into driver training and speed awareness courses.
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We review milestones in the history of increases in speed limits and travel speeds ("speed creep") and risks for road deaths and injury. Reduced speed limits, speed-camera networks, and speed calming substantially reduce these tolls in absolute numbers-a trend that is apparent in the United Kingdom, Australia, France, and other countries, but not in the United States, which has raised speed limits and does not have speed-camera networks. Newtonian relationships between the fourth power of small increases or reductions in speed and large increases or reductions in deaths state the case for speed control. Speed adaptation and the interaction between speed and other determinants of injury risks, including congestion and countermeasures, enter into these relationships. Speed-camera networks and speed calming lead to large, sustainable, and highly cost-effective drops in road deaths and injuries and should target entire populations, not merely high-risk subgroups or situations. Yet, there are major barriers to preventive strategies based on the discovery that speed kills. Modal shifts from speed on roads to speed on rail, lower maximum vehicle speeds, and speed-camera networks are required for progress toward Vision Zero-the goal of no road deaths-through Killing Speed. The human cost of the delay in killing speed in the United States may be as high as 20,000 lives lost per year.
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New road safety strategies continue to be devised by researchers and policy makers with pay-as-you-drive (PAYD) schemes gaining increasing attention. However, empirically measuring the effectiveness of these strategies is challenging due to the influence of the road environment and other factors external to the driver. The analysis presented here applies Temporal and Spatial Identifiers to control for the road environment and Driver Behaviour Profiles to provide a common measure of driving behaviour based on the risk of a casualty crash for assessing the effectiveness of a PAYD scheme on reducing driving risks. The results show that in many cases personalised feedback alone is sufficient to induce significant changes, but the largest reductions in risk are observed when drivers are also awarded a financial incentive to change behaviour. Importantly, the more frequent the exposure to the speeding information, the greater the magnitude of the change. However, the changes are disproportionately associated with those that were already safer drivers in the baseline period suggesting that some drivers may be predisposed to changing their behaviour. These results suggest that it would be beneficial to provide real-time or daily feedback on speeding behaviour in conjunction with a financial reward scheme, potentially as a component of insurance premiums.
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This paper presents a re-analysis of the Power Model of the relationship between the mean speed of traffic and road safety. Past evaluations of the model, most recently in 2009, have broadly speaking supported it. However, the most recent evaluation of the model indicated that the relationship between speed and road safety depends not only on the relative change in speed, as suggested by the Power Model, but also on initial speed. This implies that the exponent describing, for example, a 25% reduction in speed will not be the same when speed changes from 100km/h to 75km/h as it will when speed changes from 20km/h to 15km/h. This paper reports an analysis leading to a re-parameterisation of the Power Model in terms of continuously varying exponents which depend on initial speed. The re-parameterisation was accomplished by fitting exponential functions to data points in which changes in speed and accidents were sorted in groups of 10km/h according to initial speed, starting with data points referring to the highest initial speeds. The exponential functions fitted the data extremely well and imply that the effect on accidents of a given relative change in speed is largest when initial speed is highest.
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Participants made decisions between two road improvements to increase mean speed. Time saved when speed increased from a higher driving speed was overestimated in relation to time saved from increases from lower speeds. In Study 2, participants matched pairs of speed increases so that they would give the same time saving and repeated the bias. The increase in risk of an accident with person injury was underestimated and the increase in risk of a fatal accident grossly underestimated when speed increased. The increase of stopping distance when speed increased was systematically underestimated. In Study 3, the tasks and results of Study 2 were repeated with engineering students. When forming opinions about speed limits and traffic planning, drivers, the public, politicians and others who do not collect the proper facts are liable to the same biases as those demonstrated in the present study. Copyright © 2008 John Wiley & Sons, Ltd.
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In recent years we have seen important extensions of logit models in behavioural research such as incorporation of preference and scale heterogeneity, attribute processing heuristics, and estimation of willingness to pay (WTP) in WTP space. With rare exception, however, a non-linear treatment of the parameter set to allow for behavioural reality, such as embedded risk attitude and perceptual conditioning of occurrence probabilities attached to specific attributes, is absent. This is especially relevant to the recent focus in travel behaviour research on identifying the willingness to pay for reduced travel time variability, which is the source of estimates of the value of trip reliability that has been shown to take on an increasingly important role in project appraisal. This paper incorporates, in a generalised non-linear (in parameters) logit model, alternative functional forms for perceptual conditioning (known as probability weighting) and risk attitude in the utility function to account for travel time variability, and then derives an empirical estimate of the willingness to pay for trip time variability-embedded travel time savings as an alternative to separate estimates of time savings and trip time reliability. We illustrate the richness of the approach using a stated choice data set for commuter choice between unlabelled attribute packages. Statistically significant risk attitude parameters and parameters underlying decision weights are estimated for multinomial logit and mixed multinomial logit models, along with values of expected travel time savings.
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This paper provides a restatement of the case for speed limits. The paper argues that driver speed choice cannot be granted any normative status (i.e. be regarded as optimal from a societal point of view) unless it is “objectively” rational, even if it can be reasonably interpreted as “subjectively” rational. A distinction between “subjective” and “objective” rationality is very rarely made in modern analyses relying on the theory of rational choice, but it makes sense with respect to the choice of speed. Studies that have assessed which impacts of speed drivers consider, whether drivers correctly assess these impacts, and how drivers coordinate their choice of speed with other drivers are reviewed. It is concluded that driver speed choice is not “objectively” rational. It is concluded that the lack of rationality in driver speed choice implies that this choice needs to be regulated by means of speed limits.
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This paper uses state of the art stated choice designs to parameterise modal choice models for commuting and non-commuting travel futures in the presence of new public transport infrastructure (variations of new heavy rail, light rail and dedicated busway systems). D-optimal choice experiments are developed for a set of labelled modal alternatives in which respondents establish a reference benchmark based on the existing service levels (for access, linehaul and egress trip legs) which is used in a computer aided personal interview instrument to generate future scenarios of service levels for current and prospective new modals options. We show that a fully integrated stated choice experiment provides all the information required to obtain behaviourally relevant parameter estimates (within a nested logit framework) for all but the mode-specific constants (MSCs). The MSCs can be calibrated for the current modes within a network model setting, giving the transport planner an appropriate model for predicting the patronage potential for proposed new public transport infrastructure services. A useful by-product is a new set of behavioural values of travel time savings for access, egress, linehaul and wait times.
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In recent years there has been a re-focus on the valuation of a statistical life from the ex post or human capital method to an ex ante willingness to pay (WTP) approach. This is in part a recognition that we may have been undervaluing the cost of fatalities and injuries to society associated with crashes, but also a strong belief in the need to focus on establishing the amount, ex ante, that individuals are willing to pay to reduce the risk of exposure to circumstances that might lead to death or degree of injury on the road network. This study has developed a framework in which to identify the degree of preference heterogeneity in willingness to pay by individuals who are drivers or passengers in cars to avoid being killed or injured. A stated choice experiment approach is developed. The empirical setting is a choice of route for a particular trip that a sample of individuals periodically undertakes in Australia. The particular trip is described in enough detail to provide the respondent with a familiar market environment, providing all the relevant background information required for making a decision. Mixed logit models are estimated to obtain the marginal (dis)utilities associated with each influence on the choice amongst the attribute packages offered in the stated choice scenarios. These estimates are used to obtain the WTP distributions for fatality and injury avoidance, which are then aggregated to obtain estimates of the value of risk reduction (VRR), of which the fatality class is also known as the value of a statistical life (VSL).
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According to the time-saving bias, drivers overestimate the time saved when increasing from an already relatively high speed and underestimate the time saved when increasing from a relatively low speed. This study examined the effect the time-saving bias may have on drivers' choice of speed using hypothetical situations. Drivers were presented with a situation involving acceleration from a relatively low speed in order to arrive at a destination on time and were asked to estimate the time that could be saved by increasing to higher speeds. Drivers also estimated the speed required for arriving on time, the speed they would personally choose and the speed they believed other drivers would opt for in such a situation. Results showed that drivers indeed underestimated the time that could be saved by increasing from a low speed. In addition, drivers who showed a high time-saving bias (above median) indicated notably higher speeds in all three categories above and their indicated speeds exceeded the speed limit more frequently. These findings suggest that the time-saving bias may help explain why drivers, in some situations, prefer an overly high speed and violate the legal speed limit.
Article
Motor vehicle drivers make decisions about speed while traveling and thereby trade off a potential saving from shorter travel time (if the trip is uneventful) against a potential loss of time (if the trip results in a crash). The authors used computerized modeling based on national data to examine the benefits from small changes in average driver speed on public health in the United States. Lost time due to both travel and crashing was calculated, along with optimal speed to minimize net time lost. The baseline analysis suggested that 1 hour spent driving was associated with approximately 20 minutes of additional lost time in life expectancy due to the potential of a crash. A approximately 1-km/h (0.6-mph) increase in speed for the average driver yielded a approximately 26-second approximate increase (not decrease) in total expected lost time because the savings from reduced travel time were more than offset by the increased prospect of a crash. A 3.0-km/h (1.8-mph) decrease in average driving speed yielded the least amount of total time lost (95% confidence interval [CI]: 2.5-4.1 km/ h [1.5-2.5 mph]). This speed yielded about 11,000 fewer crashes each day, saved about 3.6 hours per year for the average driver (95% CI: 2.0-6.2 hours), and conserved about 199 cumulative life years for society annually. As a nation, drivers in the United States travel slightly too fast and could improve overall life expectancy by decreasing their average speed slightly.
Article
Three experiments were set up to study how drivers estimate mean travel speeds on trips with different speed limits. To specify, participants judged mean speeds of trips with speed limits on different distances of the trip. Study 1 showed that the mean speed on a road with a temporary 30 km/h speed limit was overestimated if the speeds were greater than 80 km/h on the rest of the trip. Study 2 replicated and extended the results to problems with more speed combinations. In Study 3 the distances of the speed limits were varied and the results showed that a temporary 30 km/h speed restriction gave overestimations of the mean speeds of a trip for all combinations of original and temporary speed limits over all distances. Finally, some psychological issues and applied implications for speed regulation policies were discussed.
Article
This study focused on comparative judgments about speeding risks among young drivers who have a high risk of being involved in a traffic accident. We examined (a) how these drivers assess their risk of sanctions and their risk of causing an automobile crash because of speeding in comparison to the estimated risks of other drivers, and (b) how realistic their comparative risk judgments are. We measured the relationship between the drivers' comparative risk judgments, self-reported speeding, and driving-related sensation-seeking. We hypothesized that (a) they would think they have less risk of sanctions and of causing a car accident than others, and (b) their comparative judgments of speeding risks would be linked to self-reported speeding and driving-related sensation-seeking. The study was based on a computerized questionnaire survey conducted with 3,002 young drivers (mean age=22.3) administered by professional investigators. The results confirmed our hypotheses. In order to improve the effectiveness of prevention measures and to evaluate the effect of them, road-safety interventions should take into account comparative risk judgments about the targeted risk behavior.
Article
This paper proposes a new model of driver-preferred speeds derived from the assumption that drivers trade-off a portion of their safety for a time gain. The risk of receiving a ticket for speeding is also considered. A trip disutility concept is selected to combine the three components of speed choice (safety, time, and enforcement). The perceived crash risk and speed enforcement are considered as speed deterrents while the perceived value of a time gain is considered as a speed enticement. According to this concept, speeds that minimize the perceived trip disutility are preferred by drivers. The modeled trade-off behavior does not have to be fully rational since it is affected by drivers' preferences and their ability to perceive the risk. As such, the proposed framework follows the concept of bound rationality. The attractiveness of the model lies in its parameters being estimable with the observed preferred speeds and then interpretable as the factors of risk perception, the subjective value of time, and the perceived risk of speed enforcement. The proposed method may successfully supplement behavioral studies based on a driver survey. The study focuses on four-lane rural and suburban roads in Indiana, USA. The behavior of two types of drivers (trucks and cars) is modeled. The selection of test sites was such that the roads and other local characteristics varied across the studied sites while the population of drivers could be assumed as the same. The density of intersections, land development along the road, and the presence of sidewalks were the identified prominent risk perception factors. Another interesting finding is that the speed limit seems to encourage slow drivers to drive faster and fast drivers to drive slower.
Article
A unified model of accident and travel-delay costs describes the role that defensive driving effort plays in balancing these costs, and the costs of effort itself. This motivates a simple method for jointly estimating risk, effort, and travel-delay externalities, which exploits ordinary travel-demand modeling to directly value the congestion that generates these costs. A unique empirical setting also allows for decomposing the joint externality into its travel-delay and accident-related components, with results suggesting that together risk and effort externalities are nearly on par with travel-delay externalities. It is also demonstrated that traditional value-of-time estimates substantially reflect risk and effort costs.
Article
When people judge the time that can be saved by increasing the speed of an activity, they are often victims of a time saving bias. That is, they overestimate the time that can be saved by increasing the speed. Judgments of time savings following speed increase when driving follow the Proportion heuristic [Svenson, O. (1970). A functional measurement approach to intuitive estimation as exemplified by estimated time savings. Journal of Experimental Psychology, 86, 204-210]. In a choice between time saving options, this heuristic simplifies to the Ratio rule. The first study tested this rule and found that the Ratio rule predicted incorrect decisions when planning to save traveling time in road traffic. The second study showed that the time saving bias was also present in planning of health care; to specify, in decisions about which one of two clinics to reorganize to save more of the doctors' time for personal contacts with patients. To further test the Ratio rule, Study 3 used a matching procedure in which two decision alternatives were made equal by the participants. The results supported the Ratio rule. Practical implications of the results are discussed including the Planning fallacy. In conclusion, the present set of studies have illustrated a time saving bias and provided evidence explaining why people make systematic errors when judging and deciding about time saved following a speed increase.
Article
This paper describes experiments comparing traditional computer administered stated preference with virtual experience stated preference to ascertain how people value stopped delay compared with stop-and- go or freeflow traffic. The virtual experience stated preference experiments were conducted using a wrap around driving simulator. The two methods produced two different results, with the traditional computer assisted stated preference suggesting that ramp delay is 1.6 Ð 1.7 times more onerous than freeway time, while the driving simulator based virtual experience stated preference suggested that freeway delay is more onerous than ramp delay. Several reasons are hypothesized to explain the differences, including recency, simultaneous versus sequential comparison, awareness of public opinion, the intensity of the stop-and-go traffic, and the fact that driving in the real-world is a goal directed activity. However without further research, which, if any, of these will eventually prove to be the reason is unclear. What is clear is that a comparison of the computer administered stated preference with virtual experience stated preference produces different results, even though both procedures strive to find the same answers in nominally identical sets of conditions. Because people experience the world subjectively, and make decisions based on those subjective experiences, future research should be aimed at better understanding the differences between these subjective methodologies.