Michael D Fontaine

Understanding and managing disaster evacuation on a transportation network.

Uncertain population behaviors in a regional emergency could potentially harm the performance of the regions transportation system and subsequent evacuation effort. The integration of behavioral survey data with travel demand modeling enables an assessment of transportation system performance and the identification of operational and public health countermeasures. This paper analyzes transportation system demand and system performance for emergency management in three disaster scenarios. A two-step methodology first estimates the number of trips evacuating the region, thereby capturing behavioral aspects in a scientifically defensible manner based on survey results, and second, assigns these trips to a regional highway network, using geographic information systems software, thereby making the methodology transferable to other locations. Performance measures are generated for each scenario including maps of volume-to-capacity ratios, geographic contours of evacuation time from the center of the region, and link-specific metrics such as weighted average speed and traffic volume. The methods are demonstrated on a 600 segment transportation network in Washington, DC (USA) and are applied to three scenarios involving attacks from radiological dispersion devices (e.g., dirty bombs). The results suggests that: (1) a single detonation would degrade transportation system performance two to three times more than that which occurs during a typical weekday afternoon peak hour, (2) volume on several critical arterials within the network would exceed capacity in the represented scenarios, and (3) resulting travel times to reach intended destinations imply that un-aided evacuation is impractical. These results assist decisions made by two categories of emergency responders: (1) transportation managers who provide traveler information and who make operational adjustments to improve the network (e.g., signal retiming) and (2) public health officials who maintain shelters, food and water stations, or first aid centers along evacuation routes. This approach may also interest decisionmakers who are in a position to influence the allocation of emergency resources, including healthcare providers, infrastructure owners, transit providers, and regional or local planning staff.

Investigation of Dynamic Probe Sample Requirements for Traffic Condition Monitoring

Many agencies are exploring the use of probe-based traffic monitoring systems to collect information on system performance. Although these systems offer the potential of directly measuring travel times and of significantly reducing the cost per mile of traffic monitoring systems, the issue of identifying the number of samples required to produce reliable and accurate condition information has not been adequately examined. Most existing research into this issue addresses the problem from a very broad perspective, offering a single percentage of vehicles in an area that must be equipped as probes to provide good coverage of the area. This approach ignores variations in flow conditions through time and across different links of the network. The described research addresses the issue of sample sizes for different links and measurement intervals from a rigorous statistical perspective. First, the issue of producing sample sizes on the basis of the central limit theorem (CLT) is empirically examined by using Virginia freeway speed data to assess this methods validity even when the underlying speed population is nonnormal. Applying the CLT to the speed data shows that fluctuations in flow conditions over time and across different locations require varying sample sizes, which the static sample sizes proposed in previous research do not take into account. Finally, the CLT-based sample sizes are compared with a representative static sample size proposed in the literature to illustrate how the CLT method can reduce sample sizes while maintaining the desired confidence and accuracy levels.

Interaction Between System Design and Operations of Variable Speed Limit Systems in Work Zones

Variable speed limits (VSLs) have been shown to improve safety and operations on European freeways, but work zone applications of VSLs have been limited. In July 2008, a VSL system was installed on a congested portion of the Washington, D.C., Beltway (I-95–I-495) in a major work zone. A limited field evaluation of that system revealed some deficiencies related to the systems configuration, resulting in inconclusive operational effects. Those results raised questions about the relative importance of different VSL system parameters on the ultimate effectiveness of work zone VSLs. This paper describes an evaluation that used a calibrated simulation model to evaluate the influence of several parameters. The results showed that VSLs can delay the onset of congestion and help produce more rapid recovery from congestion, provided that demand volumes are not too far above the work zone capacity. When demand volumes are extremely high, VSLs offer no appreciable benefit over static speed limits. The simulation also showed that VSL sign location is extremely important, and signs must be positioned so that drivers will accelerate back to a reasonable speed once they pass through a bottleneck. Algorithm design also proved to play an important role in system effectiveness.

Probe-Based Traffic Monitoring Systems with Wireless Location Technology: An Investigation of the Relationship Between System Design and Effectiveness

As agencies place more emphasis on monitoring and managing the roadway network, the concept of traffic monitoring systems based on wireless location technology (WLT) is generating increasing interest. WLT-based monitoring anonymously samples the location of probes or drivers by using wireless devices, such as cellular phones. By using a series of these probe vehicle locations, WLT-based monitoring systems could generate true point-to-point speed estimates with a minimal infrastructure investment. Unfortunately, early deployments of these systems have not been entirely successful in generating the quality of information needed by transportation agencies and the public. When transportation agencies are approached by vendors of WLT-based monitoring systems, they have little information to determine whether the system is likely to be effective. The relationship between the design of a WLT-based monitoring system and the accuracy of speed estimates that it generates is explored. A simulation-based approach was used to define general guidelines for different aspects of system design and roadway network characteristics. The type of map matching used, the frequency between position estimates, the error of position estimates, and roadway network geometry were shown to have a significant impact on generating accurate speed estimates from a WLT-based monitoring system.

Wireless Location Technology-Based Traffic Monitoring: Preliminary Recommendations to Transportation Agencies Based on Synthesis of Experience and Simulation Results

There has been a growing interest in using anonymous tracking of wireless devices as a way to generate travel time and operational data cost-effectively. Unfortunately, there are relatively few independent quantitative evaluations of these systems. Evaluations that do exist are often not widely available, so agencies often enter into deployment agreements with a limited understanding of the abilities and limitations of this technology. This paper provides an overview of the results of past deployments of wireless probe monitoring systems. It also discusses a simulation study of the predominant type of system on the market today, handoff-based monitoring systems. Past deployments show that early-generation systems encountered significant problems in generating accurate speed estimates. More recent tests using handoff-based technology have shown improvement in data quality at some sites, but there are not enough data to characterize fully whether those systems can consistently provide useful operational data. The simulation study indicates that the way in which the cellular network topology overlays the roadway network could be a critical determinant of overall system effectiveness. Simulation results indicate that often with simulated handoff-based systems speeds can be estimated to within 5 mph.

GUIDELINES FOR APPLICATION OF PORTABLE WORK ZONE INTELLIGENT TRANSPORTATION SYSTEMS

Work zone intelligent transportation systems (WZITSs) are promoted as a way to improve safety and reduce congestion at work zone locations where traditional traffic management centers do not exist. These systems usually integrate portable changeable message signs and speed sensors with a central control system that automatically determines appropriate messages that are based on current traffic conditions. Manufacturers of these systems claim that WZITSs can warn drivers of downstream congestion, alert drivers to slower speeds ahead, and suggest alternate routes on the basis of prevailing conditions. Transportation agencies are often asked to make decisions on the installation of a WZITS without the benefit of objective information on its expected performance. Relatively few operational tests of these systems have been performed, and the results are not always well documented or conclusive. Agencies need guidance to help them determine whether a WZITS system would improve safety and operations at a specific site. Applications of WZITSs are reviewed, and a series of guidelines for their deployment, based on lessons learned from past tests, is presented.

Long-Term Speed Compliance and Safety Impacts of Rational Speed Limits

In 2006, speeding-related crashes accounted for over 13,500 fatalities in the United States and many studies also indicate that speed and/or speed dispersion are a major cause of crashes on U.S. highways. This paper summarizes the results of a deployment of the rational speed limits (RSLs) approach on two limited access highways in Virginia. The RSL approach involves a coordinated campaign to post sound and credible speed limits, increase speed enforcement, and implement public information and education (PI&E). The goal of the RSL approach is to better regulate travel speeds, thereby improving the safety of the traveling public. While it is common to use enforcement and PI&E in attempt to improve speed limit compliance, there is not much information on whether improvements generated by these campaigns can be sustained following the end of the formal campaign. This paper presents the results of a four-year project that examined speeds, driver attitudes, and safety before, during, and after the RSL approach was implemented. Two limited access highways where speed limits were increased from 55 to 65 mph were examined. Public perception survey results showed that the new 65 mph speed limits were well supported with over 80% agreeing with the new speed limits. The speed analysis showed that the average speed increased by a statistically significant margin immediately after the speed limit was increased, but compliance with the new posted speed limit was also significantly higher than what was observed with the old, 55 mph limit. There were practically no significant changes in speed during the increased enforcement and PI&E campaign or when speeds were examined one year after the end of the campaign. In addition, the standard deviation of speeds was fairly consistent throughout the before and after periods, which suggests that crash likelihood was not increased due to the increased posted speed limit. In fact, crash data showed that safety at the two demonstration sites was actually better than anticipated based on trends at similar comparison sites where speed limits were increased but no additional enforcement or PI&E were present. The results of the study imply that compliance and safety improvements can be sustained for at least a year after a coordinated enforcement and education campaign is completed, provided that speed limits are set appropriately.

Guidelines for Using Late Merge Traffic Control in Work Zones: Results of a Simulation-Based Study

The late merge traffic control strategy has been proposed as a way to improve flow at work zone lane closures by maximizing queue storage space and creating more orderly merging. The late merge instructs drivers to use all lanes to the work zone taper and then take turns proceeding through the work zone. There is little information available on when the late merge should be used, however, and a limited understanding of the factors that influence its performance. This paper discusses the results of a simulation study of the late merge concept using microscopic traffic simulation. The late merge concept was evaluated by comparing it with traditional traffic control, through a full factorial analysis. Results of the computer simulations showed that the late merge produced a statistically significant increase in throughput volume versus the traditional merge for the three-to-one lane closure configuration across all combinations of analysis factors. Although the two-to-one and three-to-two configurations did not show significant improvement in throughput overall, it was found that as the percentage of heavy vehicles increased, the late merge did foster higher throughput volumes than traditional traffic control. The results of the simulations indicate that the late merge may not provide as much of a benefit as previous studies had indicated and that the area of application for the late merge may be limited to situations where heavy vehicles constitute more than 20% of the traffic stream.

Feasibility of real-time remote speed enforcement for work zones

Studies have shown that a large percentage of vehicles involved in work zone crashes are traveling at excessive speeds. Although traditional speed enforcement has been shown to reduce speeds through the work area, enforcement under these conditions can be dangerous to both the motoring public and enforcement officers. The work zone layout often limits the locations at which an officer can set up to enforce the speed limit and the locations at which violators can be stopped. Automated speed enforcement technology could help eliminate the need to stop violators in a work zone, but it is not currently a popular concept in the United States because of concerns about motorist privacy. Researchers hypothesized that this technology could be useful for work zone enforcement if adapted to a more real-time operation. The initial testing of the concept of remote speed enforcement is summarized. An automated speed enforcement system (consisting of digital video and lidar technology) was meshed with a wireless communications system. The unit determined when vehicles exceeded a certain speed threshold. If a vehicle was detected as exceeding the threshold, a digital photograph was taken of the violator. This photograph was then transmitted to an observer stationed downstream of the site. The technical feasibility of the system was assessed through field tests. Focus groups of law enforcement personnel were used to determine potential acceptance of the system in the law enforcement community. Recommendations for future improvements and possible applications of the system are made.

A Cyber-ITS Framework for Massive Traffic Data Analysis Using Cyber Infrastructure

Traffic data is commonly collected from widely deployed sensors in urban areas. This brings up a new research topic, data-driven intelligent transportation systems (ITSs), which means to integrate heterogeneous traffic data from different kinds of sensors and apply it for ITS applications. This research, taking into consideration the significant increase in the amount of traffic data and the complexity of data analysis, focuses mainly on the challenge of solving data-intensive and computation-intensive problems. As a solution to the problems, this paper proposes a Cyber-ITS framework to perform data analysis on Cyber Infrastructure (CI), by nature parallel-computing hardware and software systems, in the context of ITS. The techniques of the framework include data representation, domain decomposition, resource allocation, and parallel processing. All these techniques are based on data-driven and application-oriented models and are organized as a component-and-workflow-based model in order to achieve technical interoperability and data reusability. A case study of the Cyber-ITS framework is presented later based on a traffic state estimation application that uses the fusion of massive Sydney Coordinated Adaptive Traffic System (SCATS) data and GPS data. The results prove that the Cyber-ITS-based implementation can achieve a high accuracy rate of traffic state estimation and provide a significant computational speedup for the data fusion by parallel computing.