A velocidade elevada e a sua variabilidade são consideradas fatores determinantes na causa de acidentes e gravidade dos mesmos. A freqüência dos acidentes decresce quando os limites de velocidade estabelecidos são apropriados ou realísticos. O limite estabelecido deve estar de acordo com as velocidades praticadas pela média dos condutores ditos prudentes, ou este limite não será considerado. No presente estudo é elaborado um método para estabelecimento de limites de velocidade básicos para rodovias de pista simples do Estado do Rio Grande do Sul. O método parte das velocidades operacionais da via e de seus graus de mobilidade e acessibilidade, sugerindo um limite de velocidade único para os dois sentidos da via. Também são sugeridas velocidades de advertência em curvas do alinhamento horizontal. Seis rodovias do Estado do Rio Grande do Sul foram selecionadas para um estudo de caso. A seleção procura englobar rodovias de classes de projeto e região diferentes, para que se possa fazer uma análise ampla de projetos de rodovias. As rodovias, a partir de suas velocidades operacionais e dados de geometria, têm seus limites de velocidade calculados. Na seqüência, as velocidades de advertência são calculadas. Os resultados são apresentados em forma de gráficos para facilitar a compreensão da distribuição das velocidades ao longo da extensão do trecho. Os resultados de cada trecho são analisados e comparados. / High speed and its variability are considered determining factors in the cause of accidents and its severity. The frequency of accidents decreases when the speed limits established are appropriate or realistic. The limit must be established in accordance with the speeds practiced by the average conservative drivers, or this limit will not be considered. In the present study a method is developed to establish basic speed limits for two-lane highways of the state of Rio Grande do Sul. The method relies on the operational speed of the track and its degrees of mobility and accessibility, suggesting one speed limit for both ways of the road. It is also suggested warning speeds for curves in the horizontal alignment. Six two-lane highways of the state of Rio Grande do Sul were selected for a case study. The selection was made so all classes of project and different regions were included, in a way that analysis of different projects could be done. The two-lane highways have their limits of speed calculated, from their operating speeds and geometry data. Next, the warning speeds are calculated. The results are presented in the form of graphs to facilitate the understanding of the distribution of velocities along the length of the segment. The results of each different segment are analyzed and compared.

No description available.

Recent research at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical models capable of determining the crash risk on the freeway (Abdel-Aty et al., 2004; 2005, Pande and Abdel-Aty, 2006). These models are able to calculate the rear-end and lane-change crash risks along the freeway in real-time through the use of static information at various locations along the freeway as well as the real-time traffic data obtained by loop detectors. Since these models use real-time traffic data, they are capable of calculating rear-end and lane-change crash risk values as the traffic flow conditions are changing on the freeway. The objective of this study is to examine the potential benefits of variable speed limit implementation techniques for reducing the crash risk along the freeway. Variable speed limits is an ITS strategy that is typically used upstream of a queue in order to reduce the effects of congestion. By lowering the speeds of the vehicles approaching a queue, more time is given for the queue to dissipate from the front before it continues to grow from the back. This study uses variable speed limit strategies in a corridor-wide attempt to reduce rear-end and lane-change crash risks where speed differences between upstream and downstream vehicles are high. The idea of homogeneous speed zones was also introduced in this study to determine the distance over which variable speed limits should be implemented from a station of interest. This is unique since it is the first time a dynamic distance has been considered for variable speed limit implementation. Several VSL strategies were found to successfully reduce the rear-end and lane-change crash risks at low-volume traffic conditions (60% and 80% loading conditions). In every case, the most successful treatments involved the lowering of upstream speed limits by 5 mph and the raising of downstream speed limits by 5 mph. In the free-flow condition (60% loading), the best treatments involved the more liberal threshold for defining homogeneous speed zones (5 mph) and the more liberal implementation distance (entire speed zone), as well as a minimum time period of 10 minutes. This treatment was actually shown to significantly reduce the network travel time by 0.8%. It was also shown that this particular implementation strategy (lowering upstream, raising downstream) is wholly resistant to the effects of crash migration in the 60% loading scenario. In the condition approaching congestion (80% loading), the best treatment again involved the more liberal threshold for homogeneous speed zones (5 mph), yet the more conservative implementation distance (half the speed zone), along with a minimum time period of 5 minutes. This particular treatment arose as the best due to its unique capability to resist the increasing effects of crash migration in the 80% loading scenario. It was shown that the treatments implementing over half the speed zone were more robust against crash migration than other treatments. The best treatment exemplified the greatest benefit in reduced sections and the greatest resistance to crash migration in other sections. In the 80% loading scenario, the best treatment increased the network travel time by less than 0.4%, which is deemed acceptable. No treatment was found to successfully reduce the rear-end and lane-change crash risks in the congested traffic condition (90% loading). This is attributed to the fact that, in the congested state, the speed of vehicles is subject to the surrounding traffic conditions and not to the posted speed limit. Therefore, changing the posted speed limit does not affect the speed of vehicles in a desirable manner. These conclusions agree with Dilmore (2005).

This thesis focuses on evaluating the appropriate speed at which vehicles should travel under different traffic conditions on freeways and its impact on crash frequency. The common belief is that the lower speed results in fewer crashes as reduced speed provides drivers with more time to react effectively and avoid collisions. However, this perspective overlooks the interplay among traffic speed, average spacing between consecutive vehicles, and the distance available for stopping a vehicle. Hence, we propose a safety parameter termed ‘Safety Correlate' (SCORE), which is defined as the proportion of average spacing relative to the stopping distance. To determine the relationship between SCORE and crash frequency, data from 366 4-lane urban freeway segments located in Virginia was analyzed and a Random-effects Poisson Lognormal model was developed. The obtained result indicated that the safety parameter SCORE is negatively associated with the annual hourly crash frequency, implying that the lesser the average spacing as a proportion of the stopping distance while traffic flow remains constant, the more frequent will be the crashes. Additionally, this research presents an application of SCORE in setting variable speed limits under various traffic flows. Overall, the study results provide valuable insights by investigating SCORE to improve traffic safety. Also, this research would help practitioners and policymakers to incorporate safety aspects while setting variable speed limits on freeways.

During the last decades the road traffic has increased tremendously leading to congestion, safety issues and increased environmental impacts. As a result, many countries are continuously trying to find improvements and new solutions to solve these issues. One way of improving the traffic conditions is by the use of so called intelligent transport systems, where information and communication technologies are being used for traffic management and control. One such system commonly used for traffic management purposes are variable speed limit systems. These systems are making use of signs to show speed limits adjusted to the prevailing road or traffic conditions. The rapid development in telecommunication technologies has enabled communication between vehicles, and between vehicles and the infrastructure, so called cooperative systems. This opens up for  the possibility to further improve the performance of a standard variable speed limit system by adding cooperative system features. The overall aim of this thesis is to investigate the potential benefits of incorporating infrastructure to vehicle communication and autonomous control to an existing variable speed limit system. We show how such a cooperative variable speed limit system can be modeled and evaluated by the use of microscopic traffic simulation. Results from the evaluation indicate increased flow harmonization in terms of narrowing of the acceleration rate distribution and reduced exhaust emissions. Further, we compare four control algorithms for deciding on speed limits in variable speed limit systems. Differences in the resulting traffic performance between the control algorithms are quantified by the use of microscopic traffic simulation. It is concluded that the dened objective for the algorithms have a decisive influence on the effects of the variable speed limit system. The results from this thesis are useful for further development of variable speed limit systems, both with respect to incorporating cooperative features and by improving the speed setting control algorithms.

Variable speed limits (VSL) are used more commonly around the globe lately. Although on a macroscopic level positive effects of VSLs have been reported, the caveat is that the impact of VSLs is very sensitive to the level of driver compliance. Thus far it is unknown whether all individual drivers are actually able to notice when a speed limit changes into another speed limit; a prerequisite for purposeful speed limit compliance in the first place. To simulate regular driving conditions, twenty-four participants were familiarised with a particular route by driving the same route in a driving simulator nineteen times on five separate days. Part of the route consisted of a motorway where VSL signs were regularly displayed above every driving lane. At drive nineteen, speed limits changed from 80 km/h to 100 km/h on four out of eight consecutive signs. After passing all signs, one expects 6.25% of the participants still to be unaware that the speed limit had increased (based on chance), while the results showed most participants had failed to notice the speed limit change (58.3%). Instead, they saw what they expected to see: a speed limit of 80 km/h. If the speed change had been vice versa, in other words from 100 km/h to 80 km/h, this would immediately result in speed offences, though not deliberately at all.

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Bicycling as an alternate mode of transportation has been on the rise. It is environmentally friendly in nature and the associated health benefits have made it a popular choice for many types of trips. The purpose of this research is to increase understanding of the impacts of implementing bicycle corridors (as part of the Utah Department of Transportation's (UDOT) Inclusion of Active Transportation policy) on bicycle rate as a function of roadway characteristics. The results of this research will be used in determining when and where bicycle corridors will enhance the transportation system and an estimate of the overall impact of bicycle corridors on travel demand in Utah. Data collection was fundamental in this research project in determining the impacts of bicycle corridors on travel demands in the state of Utah. With limited amount of commuting bicycle data available throughout the state, it was necessary to gather bicycle volume data on corridors with and without bicycle infrastructure. In order to accomplish this data collection effort, two primary methods were used to collect bicycle volume data. The first method was to use automatic bicycle counters on roadways that had bicycle infrastructure. The second method was to gather bicycle volume data through manual counts on roads with and without bicycle infrastructure. After the bicycle volume data were collected the data were analyzed to identify trends. The first step in the analysis was to convert the bicycle volumes into rates to provide a more uniform comparison. Several analyses were run including an analysis of bicycle rate compared to Annual Average Daily Traffic (AADT), bicycle rate compared to posted speed limit, bicycle rate compared to number of vehicle lanes, and bicycle rate compared to roadway classification. A comparison of sites with bicycle infrastructure to sites without bicycle infrastructure (non-bicycle infrastructure) was also conducted to identify relationships. Comparison of bicycle rates to AADT resulted in no correlation or statistical relationship in the data but the data do suggest trends. Statistically significant results did occur when comparing bicycle rates to posted speed limits. No statistically significant relationships occurred when comparing bicycle rates to the number of lanes or roadway classification. It was determined that roadways with bicycle infrastructure tend to yield higher bicycle rates than roadways that do not have bicycle infrastructure. Lastly, using shared use path data it is determined that bicycle rates on shared use paths have increased between 1.7 to 7.5 percent from 2013 to 2014 and it is assumed that a similar trend would exist on bicycle infrastructure in the communities.

Safety in highway work zones has become a concern among Departments of Transportation (DOTs) throughout the country as the highway network has begun to age and more maintenance and construction work has been necessary. Safety in highway work zones is more compromised than in other areas for two reasons. First, the construction workers are near traveling vehicles as they perform their already dangerous work, increasing the risk of an accident. Second, the highway user is at increased risk because of the increase in roadside obstacles, because other vehicles are more likely to act in unpredictable ways (such as sudden braking or lane changes), and because vehicles are more likely to be traveling closer together (due to decreased capacity). Researchers are looking at several mechanisms for improving safety in highway work zones, including lowering the mean speed of vehicles in the work zone, encouraging drivers to be alert in work zones, improving the control of traffic in merging areas, and improving the safety devices that separate vehicles and construction workers. This study focuses on the goal of reducing speed in work zones. First, methods of speed reduction used by state DOTs throughout the country are identified, and the research surrounding them is summarized. Next, the methodology and results of a field study that tests the efficacy of the Speed Monitoring Display (SMD) are described in detail. Finally, the results of a survey that was conducted to ascertain drivers' opinions of the SMD are presented. For the field study, three main conditions were analyzed: a no-treatment case, with the MUTCD signs and barriers; a treatment case using the SMD; and a treatment case using a police vehicle. In the no-treatment case, average vehicle speed was reduced about 3 mph as vehicles entered the work area of the work zone. With the SMD, average vehicle speed was reduced an additional 4 mph. With the police vehicle, average vehicle speed was reduced about 6 mph more than in the no-treatment case. Thus, average vehicle speed was reduced in all treatment cases; however, the police vehicle was slightly more effective than the SMD at reducing average speeds. (These conclusions are valid at a 95 percent confidence level.) The results of the survey also suggest that the SMD is a promising option for state DOTs. According to drivers' self-reports, those who normally drive a little faster than the speed limit are likely to slow down in reaction to an SMD, but drivers who normally ignore the speed limit are likely to ignore an SMD. The majority of drivers surveyed had positive reactions to SMDs, reporting that they feel SMDs are accurate, not distracting, and not difficult to read.

Reduced-speed school zones greatly improve the safety of young children commuting to and from school and provide larger gaps in traffic for children to cross the street. The main focus of this study was to determine effective methods for increasing speed compliance in reduced-speed school zones. This objective was accomplished through an in-depth literature review, a public opinion survey of Utah drivers, and an evaluation of the effects of speed monitoring displays (SMDs) in school zones. The main focus of the literature review was to determine how to increase and maintain speed limit compliance within school zones. Information about the following topics with respect to school zones was researched and compiled: traffic control devices, SMDs, law enforcement, and other speed influences. A public survey was developed and implemented to evaluate the feelings and concerns of Utah drivers with respect to school-zone safety and school-zone traffic control devices. The survey was conducted in various locations throughout the state of Utah and proved to be an effective tool. The majority of those surveyed felt there was a need to improve school-zone safety in Utah. An evaluation of SMDs in four school zones throughout the state was performed. The results concluded that the SMDs analyzed in this study proved to increase speed compliance in most cases. In some cases, the SMDs maintained their effectiveness at increasing speed compliance over time; on the other hand, others lost some of their effectiveness over time, possibly due to higher percentages of commuter traffic. For the most part, speed compliance increased as manifested by the decrease in mean speed, standard deviation, 10 mph pace range, and the percentage of vehicles exceeding the 20 mph school-zone speed limit. In summary, the results of this study suggest that a combination of effective traffic control devices, public education, and appropriate law enforcement are all necessary to improve speed-limit compliance in school zones.