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Public Opinion, Traffic Performance, the Environment, and Safety After Construction of Double-Lane Roundabouts
Abstract
This study evaluated the impact of double-lane roundabout conversions on public attitudes, traffic performance, the environment, and safety at two intersections near Bellingham, Washington, and evaluated whether older drivers avoided the roundabouts by taking an alternative route. Driver support for the roundabouts increased from 34% before construction to 70% at 1 year after construction. At 1 year after construction, more than 40% of drivers did not believe the signs and pavement markings adequately conveyed information about appropriate speeds, right-of-way rules, and navigation of the roundabouts in the presence of large trucks. After other roadway changes were accounted for, substantial declines in the delays and queue lengths on minor roads, the proportion of queued vehicles, fuel consumption, and vehicle emissions were attributed to the roundabout conversions. Analyses of crash rates per million entering vehicles found that the roundabout conversions were associated with reduced rates of injury and fatal crashes combined and increased rates of property-damage-only crashes. Only the increase in the property-damage-only crash rate at one roundabout was significant. The odds that drivers age 70 years and older traveled the study corridor instead of an alternative route after the roundabout conversions were 0.32 times the odds before the conversions. These findings are generally consistent with prior research finding substantial traffic, environmental, and injury reduction benefits of single-lane roundabouts. However, the greater complexity of double-lane roundabouts may present challenges, as some confusion persisted 1 year after construction, evidence that some older drivers may have taken an alternative route to avoid them was found, and the rates of property-damage-only crashes increased.
... Today the roundabouts are among the most common road intersections. They are considered by experts to be the type of intersection that offers better performance in terms of safety (De Brabander and Vereeck, 2007;Gross et al., 2013;Jensen, 2013;Qin et al., 2013) and traffic performance (Polus and Shmueli,1997;Hu et al., 2014). Moreover, there are other positive effects provided by roundabouts, such as the reduction of air pollution and acoustic emissions (e.g., Distefano and Leonardi, 2019). ...
... There are many studies that inquired why drivers opposed to the roundabouts felt this way. Often, the same reasons were cited for both that the drivers found the intersection to be confusing, unsafe, and/or they just preferred a signalized intersection over a roundabout (Redington, 1997;Hu et al., 2014). Another reason drivers stated for opposition was a belief that the roundabout caused more congestion, yet the study in which this remark was made found significant reductions in delay and the number of vehicles stopping (Hu et al., 2014). ...
... Often, the same reasons were cited for both that the drivers found the intersection to be confusing, unsafe, and/or they just preferred a signalized intersection over a roundabout (Redington, 1997;Hu et al., 2014). Another reason drivers stated for opposition was a belief that the roundabout caused more congestion, yet the study in which this remark was made found significant reductions in delay and the number of vehicles stopping (Hu et al., 2014). Generally younger drivers were most supportive, and support was found to decrease consistently with age. ...
Roundabouts have been shown to provide significant safety and operational benefits, but a better understanding of public perceptions of roundabouts is critical in order to assess the contribution of the driving behavior of the users on their safety. Therefore, research on user behavior and preferences is a helpful tool in improving road safety and accident prevention. The aim of this study is to increase knowledge about Italian users’ public opinion on road roundabouts. The authors estimated cross-national differences, and assessed correlations with personal variables, such as age, gender, travel mode most frequently used, perception of roundabout safety, etc. In order to collecting data, the instrument used is a national web based survey, the total sample comprised 1.728 participants. The data collected were analyzed by both Ordinal regression method and Multiple Correspondence Analysis.
The results of this study show that the overall opinion that the respondents expressed against roundabouts is favorable. There are no substantial differences between the judgment of male drivers and that of females. Although for some categories of users the roundabouts are not considered safe and have no advantages in terms of functionality, their general opinion is always positive. The categories of respondents who expressed "Favorable" opinion are: women, those who travel daily with the private car or with public transport and who is a pedestrian. The categories of respondents who expressed "Very favorable" opinion are: men, and those who use the motorcycle as their main means of transport.
Moreover, this study showed that web-based surveys provide an efficient means of collecting detailed public opinion data.
... While multi-lane roundabouts had decreases in injuries relative to their control intersections, they saw increases in total and PDO crashes. Past studies have shown similar trends, where multilane roundabouts were associated with increases in total or PDO crashes (Hu et al., 2014;Isebrands & Hallmark, 2012) or with smaller reductions compared with single-lane roundabouts (Eisenman et al., 2004;Persaud et al., 2001;Rodegerdts et al., 2010) while still experiencing decreases in fatal and injury crashes. Increased complexity relative to single-lane roundabouts could have contributed to the increase in total crashes seen at multi-lane roundabouts. ...
... Another possible reason behind the effects of multi-lane roundabouts on crashes was that we examined the effects 2 years immediately after construction was completed. A lack of experience using roundabouts in general and the increased complexity of multi-lane roundabouts may present challenges for drivers in the early stages after roundabout installations (Hu et al., 2014;Retting et al., 2007), but driver behavior at roundabouts have been observed to change as roundabouts age (Belz et al., 2014;McKnight et al., 2008;Mensah et al., 2010). Hu and Cicchino (2019) found that the annual total crash count at multi-lane roundabouts decreased the longer the roundabout was in service and that the odds that a crash involved failing to yield the right-of-way or speeding at multi-lane roundabouts declined significantly over time. ...
Introduction:
Roundabouts are a proven safety countermeasure for intersection safety. This study examined the safety effects of roundabout conversions in Carmel, Indiana, also known as the "Roundabout City." Doing so is of particular interest because Carmel has a high density of roundabouts and its drivers understand their effectiveness and are familiar with navigating them. This study also adds to the current state of knowledge about innovative double-teardrop roundabouts (i.e., linked roundabouts with teardrop-shaped central islands).
Method:
Negative binomial models accounting for correlation within site pairs were applied to evaluate the safety effects of converting conventional intersections to roundabouts on total crashes, injury crashes, and property-damage-only (PDO) crashes between study sites and control sites for different roundabout types (single-lane, multi-lane, and double-teardrop). We compared crash data from a 2-year period before the installation of the roundabouts with the 2-year period after the conversions.
Results:
Injury crashes were 47% lower than what would have been expected without the roundabout conversions. The effects were strongest at the double-teardrop roundabouts, where injury crashes were significantly reduced by 84% and total crashes by 63%. Single-lane roundabouts experienced significant decreases of 51% in total crashes and 50% in PDO crashes (and a nonsignificant decrease of 50% in injury crashes). Multi-lane roundabouts were associated with increases in total and PDO crashes but a 15% decrease in injury crashes, though all were nonsignificant.
Conclusions:
Overall, the City of Carmel's roundabout program is associated with reductions in injury crashes, which indicates improvements to safety. Single-lane and double-teardrop roundabouts are associated with improvements in the occurrence and severity of crashes.
Practical applications:
Double-teardrop roundabouts should be considered for installation at interchange terminals to improve highway safety.
... The objective of this study was to update the meta-analysis study conducted in the 2000s [63], as the data used in this older study was not only outdated, but it also focused on non-US studies. A total of 44 studies (i.e., the 33 studies shown in Table 1 plus the 11 studies [51][52][53][54][55][56][57][58][59][60] shown in Table 2) were included in this meta-analysis-based research, including studies conducted in Norway, Denmark, Great Britain, Sweden, Germany, Switzerland, the Netherlands, Belgium, Australia, and the US. These studies were conducted between 1975 and 2014. ...
Several research studies conducted in North America and Europe have consistently shown that converting signalized intersections into roundabouts leads to safety benefits. These studies have led North American and European transportation agencies to convert hundreds of signalized intersections into roundabouts over the last few decades. Meanwhile, the Emirate of Abu Dhabi, the largest emirate in the United Arab Emirates (UAE), has replaced many of its long-standing roundabouts with signalized intersections (i.e., controlled by traffic lights) despite the fact that no UAE-based scientific study comparing the safety performance of these two intersection types can be found in the literature. Hence, the objectives of this paper are to (i) identify factors that significantly contribute to fatal intersection-related crashes and (ii) assess the in-service safety performance of signalized intersections and roundabouts. It is anticipated that the findings from this research will provide road designers and decision-makers with much needed scientific guidance on which factors contribute to fatal intersection crashes as well as on whether converting existing roundabouts into signalized intersections improves public safety or not in Abu Dhabi. The findings from this research should also benefit neighboring Gulf Cooperation Council (GCC) countries considering their similarities in road design, traffic characteristics, and driving culture.
... Studies of roundabouts in various countries have shown that roundabouts can significantly improve functional characteristics (Easa and Mehmood, 2006;Ma et al., 2013), as well as traffic safety (Chen et al., 2013;Gross et al., 2013). Lot of researchers also examined the public opinion on roundabouts (Distefano et al, 2019a;Distefano et al., 2019b;Hu et al., 2014;Retting et al., 2002). and the relationship between geometric elements and safety benefits in roundabouts (e.g. ...
Road traffic injuries claim more than 1.2 million lives each year in the world and have a huge impact on health and development. It is commonly acknowledged that the human factor and the interaction between the human factor and the road environment are among the most common causes of road accidents. Intersections are among the most complex road environments: their geometric and traffic characteristics weigh the driver workload, affecting the driving behaviour and consequently the risk of accident. This study intends therefore to contribute for a better understanding of the relationship between different types of intersection and the human factor. The ultimate aim is to understand how at grade intersections affect the driving behaviour by comparing the drivers’ stress level for roundabouts and standard intersections. Electrodermal activity can provide a real-time assessment of the driver's stress level. Electrodermal activity was therefore collected continuously during a driving study which took place on a test environment based at Cranfield University and surrounding roads. Twenty participants were involved within the study. The analysis focused on four crossing manoeuvres on three at grade intersections (two T-junctions and a roundabout) situated on the study location. Results showed that the number of SCR peaks as well as the amplitude of the peaks are overall higher for the two manoeuvres on the roundabout. The stress level induced by each type of intersection was evaluated through an Electrodermal Impact Index which takes into account both the number and the amplitude of SCR peaks. Results suggested that the stress level induced by roundabouts is more than double that induced by standard intersections.
... Transportation (Ahn et al., 2009;Alam et al., 2014;Barth and Boriboonsomsin, 2009;Bel et al., 2015;Blake, 2008;Cascetta et al., 2010;Chen et al., 2012;Chong-White et al., 2012, p.;Chou et al., 2010;Chu, 2015;Coelho et al., 2005;Day et al., 2011;Ellison et al., 2013;Fernandes et al., 2016;Garcia-Castro et al., 2014;Hallmark et al., 2011;Herzog et al., 2006;Hu et al., 2014;Innamaa and Penttinen, 2014;Jazcilevich et al., 2015;Joy and Schreffler, 2015;Kendrick et al., 2014;Koenders et al., 2012;Malina and Scheffler, 2015;Nelson et al., 2007;Percoco, 2013;Rotaris et al., 2010;Strömberg and Karlsson, 2013;Sun et al., 2014;Xu et al., 2013) Environmental science (Atkinson et al., 2009;Baldasano et al., 2010;Barratt et al., 2007;Beevers and Carslaw, 2005;Boogaard et al., 2012;Cai and Xie, 2011;Dijkema et al., 2008;Ferreira et al., 2015;Invernizzi et al., 2011;Johansson et al., 2009;Keuken et al., 2010Keuken et al., , 2012Norman et al., 2016;Owen, 2005;Panteliadis et al., 2014;Qadir et al., 2013;SLB Analysis, 2006;Titos et al., 2015;Wang et al., 2010;Yao et al., 2013) Economics and public policy (Asensio et al., 2014;Castillo-Manzano et al., 2014;Davis, 2008;Fontes et al., 2015;Gallego et al., 2013;Peters and Kramer, 2005 Table 4 gives the results of the TMS evaluations; details of all evaluations are given in the Supplementary Material. The WEL for exposure and health effects is Insufficient for all TMS. ...
This paper reviews the effectiveness of traffic management strategies (TMS) for mitigating emissions, ambient concentrations, human exposure, and health effects of traffic-related air pollution in urban areas. The objective is to summarize the evidence base for a range of moderate-scale strategies broadly relevant to municipal and regional government decision-making. A systematic literature search was carried out to identify empirical studies of TMS effects on emissions, air quality, exposure, or health. Identified studies were reviewed to assess the state of evidence that TMS can improve urban air quality and pollution-related health outcomes for exposed populations. Overall, the evidence base is weak for these effects. There is limited evidence of effects on emissions for 7 of the 22 studied strategies, and limited evidence of effects on air quality for 2 of the strategies: area road pricing and low emission zones. Insufficient evidence exists for all other TMS and effects. Existing evidence suggests that aggressive area-based TMS such as low emission zones are needed to generate substantial air quality benefits, and that TMS must be implemented with care to avoid unintended detrimental and rebound effects. The evidence base is limited by a lack of ex post evaluations of implemented strategies, lack of evaluation of exposure and health impacts, small intervention effects relative to the influences of other factors, and insufficient evaluation of spillover and indirect effects. Evolving vehicle fleets add further uncertainty to the long-range effects of TMS on air quality. Effects of TMS on measured population exposure and public health outcomes have not been well-studied. An evidence-based approach to transportation systems planning necessitates additional resource allocation to ex post evaluations and performance monitoring for air quality impacts of traffic management strategies.
... The results showed that roundabouts improved the efficiency of traffic flow and reduced vehicle emissions and fuel consumption. Installing roundabouts in place of intersections governed by traffic lights or stop signs was found to reduce carbon monoxide emissions by 15-45 per cent, nitrous oxide emissions by 33-44 per cent, carbon dioxide emissions by 23-34 per cent, and hydrocarbon emissions by 0-40 per cent [8]. ...
Vehicle fuel consumption and emission rates in Kuwait have increased considerably over recent decades, and are now causing health and economic problems. A three-lane smart roundabout is a new and innovative design idea that can help to mitigate these issues. The smart roundabout was designed with a dedicated exit lane on the right side of each entryway, and a U-turn path connecting each adjacent entry and exit road. Both features permit vehicles to turn in specific directions without needing to enter the roundabout itself. Underground tunnels were designed for pedestrian and cyclist use. The objective of this study was to measure the impact of a smart roundabout on vehicle fuel consumption and on emissions of carbon dioxide, carbon monoxide, nitrogen oxides, and hydrocarbons. These results were then compared with those of a traditional roundabout and of a light-signalised intersection. Two light-signalised intersections with different traffic volumes were chosen for this study and simulated in their present state, as replaced by traditional roundabouts; and as replaced by smart roundabouts using the SIDRA 6.0 software. The smart roundabout allowed traffic to proceed with minimal delay and idling time, significantly reducing vehicle fuel consumption and emissions in comparison with a traditional roundabout or light-signalised intersection. Furthermore, the smart roundabout allowed pedestrians and cyclists to move safely through the intersection without interacting with vehicular traffic. © 2015, South African Institute of Industrial Engineering. All rights reserved.
... Converting intersections controlled by traffic signals or stop signs to roundabouts greatly reduces injury crashes (Persaud et al., 2001). Older drivers favor roundabouts somewhat less than younger drivers and may use alternate routes to avoid them (Hu et al., 2014;Retting et al., 2007), but adding features to roundabouts such as advanced warning signs or directional signs may encourage older drivers to use them (Lord et al., 2007). ...
Older drivers are at increased risk of crash involvement per mile traveled. The purpose of this study was to examine older driver errors in serious crashes to determine which errors are most prevalent.
The National Highway Traffic Safety Administration's National Motor Vehicle Crash Causation Survey collected in-depth, on-scene data for a nationally representative sample of 5470 U.S. police-reported passenger vehicle crashes during 2005-2007 for which emergency medical services were dispatched. There were 620 crashes involving 647 drivers aged 70 and older, representing 250,504 crash-involved older drivers. The proportion of various critical errors made by drivers aged 70 and older were compared with those made by drivers aged 35-54.
Driver error was the critical reason for 97% of crashes involving older drivers. Among older drivers who made critical errors, the most common were inadequate surveillance (33%) and misjudgment of the length of a gap between vehicles or of another vehicle's speed, illegal maneuvers, medical events, and daydreaming (6% each). Inadequate surveillance (33% vs. 22%) and gap or speed misjudgment errors (6% vs. 3%) were more prevalent among older drivers than middle-aged drivers. Seventy-one percent of older drivers' inadequate surveillance errors were due to looking and not seeing another vehicle or failing to see a traffic control rather than failing to look, compared with 40% of inadequate surveillance errors among middle-aged drivers. About two-thirds (66%) of older drivers' inadequate surveillance errors and 77% of their gap or speed misjudgment errors were made when turning left at intersections. When older drivers traveled off the edge of the road or traveled over the lane line, this was most commonly due to non-performance errors such as medical events (51% and 44%, respectively), whereas middle-aged drivers were involved in these crash types for other reasons. Gap or speed misjudgment errors and inadequate surveillance errors were significantly more prevalent among female older drivers than among female middle-aged drivers, but the prevalence of these errors did not differ significantly between older and middle-aged male drivers. These errors comprised 51% of errors among older female drivers but only 31% among older male drivers.
Efforts to reduce older driver crash involvements should focus on diminishing the likelihood of the most common driver errors. Countermeasures that simplify or remove the need to make left turns across traffic such as roundabouts, protected left turn signals, and diverging diamond intersection designs could decrease the frequency of inadequate surveillance and gap or speed misjudgment errors. In the future, vehicle-to-vehicle and vehicle-to-infrastructure communications may also help protect older drivers from these errors.
Copyright © 2015 Elsevier Ltd. All rights reserved.
At the roundabouts introduced so far, some kinds of effects in safety such as decreasing the travel speed or reducing the number of accidents have been reported compared to before the introduction. However, drivers might become accustomed to driving a roundabout after a certain period since the introduction. Therefore, monitoring the changes in vehicle behavior over time is considered to be important. In this study, investigation on changes in vehicle behavior such as speed, acceleration, and position over time using videos taken with a drone about 22 months, 28 months, and 55 months after the introduction was conducted. The result shows that the speed at the entry leg approach has increased, but the speed at the circulatory road or the exit leg has not changed so much.
The World Health Organization (WHO) reported that globally 3.7 million deaths were attributable to ambient air pollution (AAP) in 2012. Traffic congestion is one of the significant sources of air pollutants Intelligent Transportation Systems (ITS) are advanced technologies that have been used widely in large cities. They have a potential impact on reducing traffic congestion and then improving environmental quality. Many countries have targeted urban policy traffic enforcement strategies that are ITS-based on improving traffic emission and air quality. Because each strategy has a different impact level, the strategy that positively impacts location and traffic conditions might negatively impact under different conditions. Also, the authorities that take the decision which strategies could be implemented. Therefore, this paper aims to evaluate the potential impact of traffic enforcement strategies on reducing traffic emissions and improving air quality. In our study, three typical traffic enforcement strategies were evaluated: a traffic management regulation for speed limit changes, route changing, and fleet composition changes. The impact of these strategies on air quality was evaluated through evaluating the traffic air quality changes brought by these strategies against a baseline (Base Case) scenario. The results indicate that the impact of these strategies on increasing environmental quality is not always positive. The reduction of CO was the highest in the speed restriction scenario (25.6%) than other scenarios. While reducing the reduction of PM10 was less in speed restriction scenario (25.6%) than other scenarios. The findings can help the decision makers implement the best strategy to reduce traffic emission under different situations.
Introduction:
Despite the proven safety benefits, crashes still occur at roundabouts. This study examined long-term trends in total crash counts, crash severity, and crashes involving common driver errors (failing to yield the right-of-way and speeding) in the period following the completion of single- and double-lane roundabouts in Washington state.
Method:
Crashes occurring during 2010-2016 at single- and double-lane roundabouts completed between 2009 and 2015 in Washington state were included. Poisson regression examined changes in annual total crash counts over time. Logistic regression estimated average annual changes in the odds that a crash involved an evident/incapacitating/fatal injury and that a crash involved a driver error. Regression models were estimated for single- and double-lane roundabouts separately.
Results:
Annual total crash counts declined significantly by 8.8% over time at double-lane roundabouts and increased nonsignificantly over time at single-lane roundabouts. The study estimated a significant 32.1% annual reduction in the odds that a crash involved an evident or incapacitating injury at double-lane roundabouts and a nonsignificant 18.9% reduction at single-lane roundabouts. There was a significant 10.6% annual decline in the odds that a crash was right-of-way related at double-lane roundabouts and a significant 19.1% annual decline in the odds that a crash was speeding-related at single-lane roundabouts.
Conclusions:
The current study demonstrates that safety can improve over time at double-lane roundabouts as drivers gain experience navigating them. At the same time, it is important that roundabouts include design elements that will prevent right-of-way mistakes and reduce speeds. Practical applications: Communities installing double-lane roundabouts may find that their benefits will increase the longer they are in place, even if initial changes in crashes and injuries are underwhelming.
This paper presents a meta-analysis of the road safety effects of converting junctions to roundabouts. 44 studies containing a total of 154 estimates of effect were included. Based on a meta-regression analysis, converting junctions to roundabouts is associated with a reduction of fatal accidents of about 65% and a reduction of injury accidents of about 40%. The mean effect on property-damage-only accidents is ambiguous. Summary estimates of effect are robust for fatal and injury accidents, but vary depending on the model of meta-analysis and the treatment of outlying data points for property-damage-only accidents. A trim-and-fill analysis suggests a weak tendency for publication bias, with modest influence on summary estimates of effect. It is concluded that roundabouts are very effective in reducing traffic fatalities.
Public opinion becomes increasingly salient in the ex post evaluation stage of large infrastructure projects which have significant impacts to the environment and the society. However, traditional survey methods are inefficient in collection and assessment of the public opinion due to its large quantity and diversity. Recently, Social media platforms provide a rich data source for monitoring and assessing the public opinion on controversial infrastructure projects. This paper proposes an assessment framework to transform unstructured online public opinions on large infrastructure projects into sentimental and topical indicators for enhancing practices of ex post evaluation and public participation. The framework uses web crawlers to collect online comments related to a large infrastructure project and employs two natural language processing technologies, including sentiment analysis and topic modeling, with spatio-temporal analysis, to transform these comments into indicators for assessing online public opinion on the project. Based on the framework, we investigate the online public opinion of the Three Gorges Project on China's largest microblogging site, namely, Weibo. Assessment results present spatial-temporal distributions of post intensity and sentiment polarity, reveals major topics with different sentiments and summarizes managerial implications, for ex post evaluation of the world's largest hydropower project. The proposed assessment framework is expected to be widely applied as a methodological strategy to assess public opinion in the ex post evaluation stage of large infrastructure projects.
Older drivers are overinvolved in intersection crashes compared with younger drivers, but the reasons are not clearly understood. The purpose of the present study was to identify the factors that lead to older drivers' intersection crashes.
Study participants were composed of two groups of older drivers -- ages 70-79 (n = 78) and 80 and older (n = 76) -- and a comparison group of drivers ages 35-54 (n = 73); all were at fault in intersection crashes involving nonfatal injuries. Police crash reports, telephone interviews with at-fault drivers, and photographs of intersections were used to determine the kinds of driver actions and errors that led to the intersection crashes.
Drivers 80 and older had fewer rear-end crashes than drivers ages 35-54 and 70-79, and both groups of older drivers had fewer ran-off-road crashes than drivers ages 35-54. Crashes where drivers failed to yield the right-of-way increased with age and occurred mostly at stop sign-controlled intersections, generally when drivers were turning left. The reasons for failure-to-yield crashes tended to vary by age. Compared with drivers ages 35-54 and 80 and older, drivers ages 70-79 made more evaluation errors -- seeing another vehicle but misjudging whether there was adequate time to proceed. In contrast, drivers 80 and older predominantly failed to see or detect the other vehicle. Drivers ages 35-54 also tended to make search errors, but theirs were due more often to distraction.
Factors leading to intersection crashes vary with age, even between two age groups of older drivers. Because the number of older drivers is projected to increase, it is important to identify ways to reduce the frequency and severity of their intersection crashes. Roundabouts and protected left turn lanes at signalized intersections may help to reduce failure-to-yield crashes at intersections, especially among older drivers. Crash avoidance systems may help to reduce crashes for drivers of all ages, but most systems have not been thoroughly investigated using real-world crash data.
Roundabouts can provide substantial safety and traffic flow benefits compared with conventional intersections, but they often are opposed in the planning stage by local residents and elected officials who question their effectiveness. The purpose of the present study was to measure public opinion before and after construction of roundabouts in several communities and to evaluate the impact of roundabout construction on traffic flow. Three communities where stop-sign- or traffic-signal-controlled intersections were replaced with roundabouts in 2004 were the subjects of this research. Overall, 36 percent of drivers supported the roundabouts before construction compared with 50 percent shortly after construction. Roundabouts had very positive effects on traffic flow. Average intersection delays during peak hours at the three sites were reduced by 83-93 percent. Traffic congestion, as measured by the vehicle-to-capacity ratio, was reduced by 58-84 percent These results provide further evidence that roundabouts can improve traffic flow and that public support for roundabouts increases after they are in place.
Roundabouts have proved to be effective in urban and suburban environments in the United States, but little has been reported on the effectiveness of roundabouts in rural environments on high-speed roadways. There is no question that roundabouts reduce the speeds of all vehicles at intersections and reduce the frequency of fatal and injury-related crashes. This research is the first comprehensive look at roundabouts in a rural environment with high-speed approaches. Nineteen intersections had ample comprehensive crash data to be evaluated and analyzed for safety performance. The findings validated the hypothesis that roundabouts in a rural environment as well as roundabouts in urban and suburban environments outperformed other intersection safety improvements. A before-and-after crash analysis was conducted for the 19 intersections by using a negative binomial regression model. Results showed statistically significant reductions for the total number of crashes (63%) and injury crashes (88%) when roundabouts were implemented. A before-and-after empirical Bayes estimation was also conducted, and the results were consistent, indicating a 62% to 67% reduction in total crashes and an 85% to 87% reduction in injury crashes at these rural intersections. Furthermore, results showed that injury-producing crash types, such as the angle crash, were reduced by 91%, and were statistically significant. Finally, this research produced crash prediction models at planning level for total and injury crashes at rural roundabouts on high-speed roadways. This supplements the models produced in NCHRP Report 572: Roundabouts in the United States and reported in the AASHTO Highway Safety Manual.
Roundabouts can provide substantial safety and traffic flow benefits compared with traffic signals and stop signs and as a result are increasingly used in place of traditional intersections. However, construction of roundabouts can be hampered by the negative perceptions held by some drivers. Prior research has found that public support increases soon after roundabouts are built and drivers become familiar with them. The purpose of the current study was to measure longer-term changes in public opinion in six communities where stop signs or traffic signals were replaced with roundabouts. Telephone surveys were conducted approximately 6 weeks before, 6 weeks after, and 1 to 5 years after construction of the roundabouts. The proportion of drivers in favor of roundabouts ranged from 22% to 44% before construction compared with 48% to 67% soon after roundabouts were built and 57% to 87% after roundabouts were in place for at least 1 year. The majority of drivers of all ages favored roundabouts after they were in place for 1 year or more, although support was higher among younger drivers (ages 18 to 34) and lower among older drivers (65 and older). There were small but nonsignificant differences between the opinions of male and female drivers. Drivers who said the roundabouts improved safety or traffic flow, or both, had more favorable opinions of roundabouts 1 to 5 years after construction. Results indicate that public support continued to increase with time, presumably because drivers became more familiar and comfortable with this form of traffic control.
Modern roundabouts are designed to control traffic flow at intersections without the use of stop signs or traffic signals. U.S. experience with modern roundabouts is rather limited to date, but in recent years there has been growing interest in their potential benefits and a relatively large increase in roundabout construction. This interest has created a need for data regarding the safety effect of roundabouts. Changes in motor vehicle crashes following conversion of 23 intersections from stop sign and traffic signal control to modern roundabouts are evaluated. The settings, located in seven states, are a mix of urban, suburban, and rural environments with the urban sample consisting of both single-lane and multilane designs and the rural sample consisting of only single-lane designs. A before-after study was conducted using the empirical Bayes procedure, which accounts for regression to the mean and traffic volume changes that usually accompany conversion of intersections to roundabouts. For the 23 intersections combined, this procedure estimated highly significant reductions of 40 percent for all crash severities combined and 80 percent for all injury crashes. Reductions in the numbers of fatal and incapacitating injury crashes were estimated to be about 90 percent. In general, the results are consistent with numerous international studies and suggest that roundabout installation should be strongly promoted as an effective safety treatment for intersections. Because the empirical Bayes approach is relatively new in safety analysis, the potential of this methodology in the evaluation of safety measures is demonstrated.
A study was performed to determine public opinion regarding modern roundabouts, both before and after their construction, in several communities and to evaluate the impact of roundabout construction on traffic flow and intersection performance. Both telephone and field surveys were performed. Roundabouts reduced overall vehicle delays, reduced the proportion of drivers that came to a stop and reduced the level of traffic congestion.
To better understand the characteristics of crashes involving senior drivers 65 and older, studies of these crashes were reviewed.
The review focused primarily on North American studies published since 1990. Studies point to important differences between the crashes of senior drivers and those of younger drivers.
Numerous studies have found that senior drivers' crashes are much more likely than crashes of younger drivers to occur at intersections. Senior drivers have particularly high rates of involvement in intersection crashes when they are turning, and even more so when they are turning left. Senior drivers are more likely than younger drivers to have been at fault in these situations, typically because they failed to yield the right-of-way, disregarded the traffic signal, or committed some other traffic violation. Studies also suggest that the extent of overinvolvement of senior drivers in certain types of crashes generally increases with advancing age.
The extent to which the distinctive characteristics of senior drivers' crashes may be due to changing travel patterns associated with aging, or physical or cognitive impairments related to the aging process, is unclear. Further research is needed to understand the pre-crash circumstances of older drivers' intersection crashes.