Research recently conducted at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical and neural networks models that are 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 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 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 combining two ITS strategies (Ramp Metering and Variable Speed Limits strategies) for reducing the crash risk (both rear-end and lane-change crash risks) along the I-4 freeway. Following this aspect, a 36.25-mile section of I-4 running though Orlando, FL was simulated using the PARAMICS micro-simulation program. Gayah (2006) used the same network to examine the potential benefits of two ITS strategies separately (Route Diversion and Ramp Metering) for reducing the crash risk along the freeway by changing traffic flow parameters. Cunningham (2007) also used the same network to examine the potential benefits of implementing Variable Speed Limits strategy for reducing the crash risk along the freeway. Since the same network is used, the calibration and validation procedures used in this study are the same as these previous two studies. This study simulates three volume loading scenarios on the I-4 freeway. These are 60, 80 and 90 percent loading scenarios. From the final experimental design for the 60 % loading, it was concluded that implementing VSL strategy only was more beneficial to the network than either implementing Ramp Metering everywhere (through the whole network) in conjunction with VSL everywhere or implementing Ramp Metering downtown (in downtown areas only) in conjunction with VSL everywhere. This was concluded from the comparison of the results of this study with the results from Cunningham (2007). However, either implementing Ramp Metering everywhere or downtown in conjunction with VSL everywhere showed safety benefits across the simulated network as well as a reduction in the total travel time. The best case for implementing Ramp Metering everywhere in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of half speed zone and a speed change time of 5 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. And the best case for implementing Ramp Metering downtown in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of half speed zone and a speed change time of 10 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. For the 80 % loading, it was concluded that either implementing Ramp Metering everywhere in conjunction with VSL everywhere or implementing Ramp Metering downtown in conjunction with VSL everywhere was more beneficial to the network than implementing VSL strategy only. This was also concluded from the comparison of the results of this study with the results from Cunningham (2007). Moreover, it was concluded that implementing Ramp Metering everywhere in conjunction with VSL everywhere showed higher safety benefits across the simulated network than implementing Ramp Metering downtown in conjunction with VSL everywhere. Also, both of them increased the total travel time a bit, but this was deemed acceptable. Additionally, both of them had successive fluctuations and variations in the average lane-change crash risk vs. time step. The best case for implementing Ramp Metering everywhere in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 5 mph, a speed change distance of half speed zone and a speed change time of 30 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. And the best case for implementing Ramp Metering downtown in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 5 mph, a speed change distance of half speed zone and a speed change time of 30 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. Searching for the best way to implement both Ramp Metering and VSL strategies in conjunction with each other, an indepth investigation was conducted in order to remove the fluctuations and variations in the crash risk with time step (through the entire simulation period). The entire simulation period is 3 hours, and each time step is 5 minutes, so there are 36 time steps representing the entire simulation period. This indepth investigation led to the idea of not implementing VSL at consecutive zones (using either a gap of one zone or more). Then this idea was applied for the best case of implementing Ramp Metering and VSL everywhere at the 80 % loading, and the successive fluctuations and variations in the crash risk with time step were removed. Moreover, much better safety benefits were found. So, this confirms that this idea was very beneficial to the network. For the 90 % loading, it was concluded that implementing Ramp Metering strategy only (Zone algorithm in downtown areas, and ALINEA algorithm in non downtown areas) was more beneficial to the network than implementing Ramp Metering everywhere in conjunction with VSL everywhere. This was concluded from the comparison of the results of this study with the results from Gayah (2006). However, implementing Ramp Metering everywhere in conjunction with VSL everywhere showed safety benefits across the simulated network as well as a reduction in the total travel time. The best case was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of the entire speed zone and a speed change time of 20 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. In summary, Ramp Metering was more beneficial at congested situations, while Variable Speed Limits were more beneficial at free-flow conditions. At conditions approaching congestion, the combination of Ramp Metering and Variable Speed Limits produced the best benefits. These results illustrate the significant potential of ITS strategies to improve the safety and efficiency of urban freeways.

Variable Speed Limit Sign (VSLS) systems enable transportation managers to dynamically change the posted speed limit in response to prevailing traffic and/or weather conditions. VSLS are thought to improve safety and reduce driver stress while improving traffic flow and travel times. Although VSLS have been implemented in a limited number of jurisdictions throughout the world, there is currently very limited documentation describing the quantitative safety and operational impacts. The impacts that have been reported are primarily from systems in Europe, and may not be directly transferable to other jurisdictions, such as North America. Furthermore, although a number of modelling studies have been performed to date that quantify the impacts of VSLS, the VSLS control strategies are often too complex or based on unrealistic assumptions and therefore cannot be directly applied for practical applications. Consequently, a need exists for an evaluation framework that quantifies the safety and traffic performance impacts of comprehensive VSLS control strategies suitable for practical applications in North America. This paper presents the results of an evaluation of a candidate VSLS system for an urban freeway in Toronto, Canada. The evaluation was conducted using a microscopic simulation model (i. e. a model that predicts individual vehicle movements) combined with a categorical crash potential model for estimating safety impacts. <br /><br /> The objectives of this thesis are: 1) to validate a real-time crash prediction model for a candidate section of freeway; 2) to develop a candidate VSLS control algorithm with potential for practical applications; 3) to evaluate the performance of the VSLS control strategy for a range of traffic conditions in terms of safety and travel time; and 4) to test the sensitivity of the VSLS impact results to modifications of the control algorithm. <br /><br /> The analysis of the VSLS impacts under varying levels of traffic congestion indicated that the candidate control strategy was able to provide large safety benefits without a significant travel time penalty, but only for a limited range of traffic conditions. The tested algorithm was found to be insufficiently robust to operate effectively over a wide range of traffic conditions. However, by modifying parameters of the control algorithm, preliminary analysis identified potential improvements in the performance of the VSLS. The modified control strategy resulted in less overall travel time penalty without an adverse impact on the safety benefits. It is anticipated that further modifications to the VSLS control strategy could result in a VSLS that is able to operate over a wide range of traffic conditions and provide more consistent safety and travel time benefits, and it is recommended that the framework used in this study is an effective tool for optimizing the algorithm structure and parameter values.

Variable Speed Limit Sign (VSLS) systems enable transportation managers to dynamically change the posted speed limit in response to prevailing traffic and/or weather conditions. VSLS are thought to improve safety and reduce driver stress while improving traffic flow and travel times. Although VSLS have been implemented in a limited number of jurisdictions throughout the world, there is currently very limited documentation describing the quantitative safety and operational impacts. The impacts that have been reported are primarily from systems in Europe, and may not be directly transferable to other jurisdictions, such as North America. Furthermore, although a number of modelling studies have been performed to date that quantify the impacts of VSLS, the VSLS control strategies are often too complex or based on unrealistic assumptions and therefore cannot be directly applied for practical applications. Consequently, a need exists for an evaluation framework that quantifies the safety and traffic performance impacts of comprehensive VSLS control strategies suitable for practical applications in North America. This paper presents the results of an evaluation of a candidate VSLS system for an urban freeway in Toronto, Canada. The evaluation was conducted using a microscopic simulation model (i. e. a model that predicts individual vehicle movements) combined with a categorical crash potential model for estimating safety impacts. <br /><br /> The objectives of this thesis are: 1) to validate a real-time crash prediction model for a candidate section of freeway; 2) to develop a candidate VSLS control algorithm with potential for practical applications; 3) to evaluate the performance of the VSLS control strategy for a range of traffic conditions in terms of safety and travel time; and 4) to test the sensitivity of the VSLS impact results to modifications of the control algorithm. <br /><br /> The analysis of the VSLS impacts under varying levels of traffic congestion indicated that the candidate control strategy was able to provide large safety benefits without a significant travel time penalty, but only for a limited range of traffic conditions. The tested algorithm was found to be insufficiently robust to operate effectively over a wide range of traffic conditions. However, by modifying parameters of the control algorithm, preliminary analysis identified potential improvements in the performance of the VSLS. The modified control strategy resulted in less overall travel time penalty without an adverse impact on the safety benefits. It is anticipated that further modifications to the VSLS control strategy could result in a VSLS that is able to operate over a wide range of traffic conditions and provide more consistent safety and travel time benefits, and it is recommended that the framework used in this study is an effective tool for optimizing the algorithm structure and parameter values.

Thesis (M.S.)--Florida State University, 2003. / Advisor: Renatus N. Mussa, Florida State University, Dept. of Civil Engineering. Title and description from dissertation home page (viewed Mar. 8, 2004). Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2003. / Includes bibliographical references (p. 85-89).

Overuse of the Interstate and National Highway Systems has led many urban freeways to suffer from recurrent congestion and high crash rates. One method of ameliorating these problems is through the use of Active Traffic Management (ATM). Within ATM, the practice of speed harmonization is well suited to improving safety and reducing delay. In this study, speed harmonization is applied to a segment of Interstate Highway 35, just south of downtown Austin, Texas. First, the need for congestion and safety improvements will be established. Then, the framework of a speed harmonization system will be developed through a synthesis of speed harmonization best practice. Next, the speed harmonization framework will be evaluated for its impact on efficiency through the development of before and after micro-simulation models. Finally, the trajectory files generated from simulation will be analyzed using surrogate safety measures to assess the safety impact of the proposed speed harmonization system. / text

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 182-190). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 66-73). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 66-73). Also available on the Internet.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2006. / Includes bibliographical references (p. 89-91).