Scott A. Parr

Critical Intersection Signal Optimization During Urban Evacuation Utilizing Dynamic Programming

Despite advancements in the field of traffic planning and operations, many major cities still rely on pretimed signal settings. With only pretimed signal control strategies, the secondary effects of a terror attack are magnified by slow evacuation times resulting in further loss of life. However, the cost of implementing new infrastructure based solely on the chance of a no-notice evacuation is not something that city planners are willing to do. The purpose of the research is to define a cost-effective methodology to develop pretimed signal control strategies to assist evacuations in urban areas. To that end, a dynamic programming methodology was developed to assist critical intersections in urban corridors. To test this methodology, a microscopic traffic-simulation environment was created for a case study of a 10 intersection evacuation corridor in Washington, DC. Using the proposed methodology to optimizing signal splits of a critical intersection within an evacuation corridor, evacuation clearance time was reduced by approximately 1 h. Furthermore, this formulation can be used to develop pretimed signal control settings for evacuation scenarios. Results showed that peak-hour signal timings are not sufficient in the case of an emergency, and signal timing plans must be tailored for emergency evacuation.

Application of Transit Signal Priority for No-Notice Urban Evacuation

During an urban evacuation, is it advisable for regional planners to allow transit buses signal priority in cases where police-assisted traffic controls are not an option? With only a finite number of available units, buses will be required to make multiple trips in and out of evacuation zones. Therefore, it is within reason that some regional municipalities would want to allow transit priority to hasten trips made by buses. However, studies in the past have shown that, during times of high roadway demand, transit priority causes major delays for vehicular traffic. The goal of this paper is to examine and quantify the benefit of transit signal priority will have on transit vehicles and any hindrance this priority has on nontransit evacuees. By applying state-of-the-art tools in evacuation modeling and microscopic traffic simulation, the aspects of a multimodel evacuation and transit signal priority impact study are merged within a single study of Washington, DC. On the basis of simulation results, transit signal priority has the potential to save lives by reducing bus travel time by 26%. This signifies that three prioritized buses can handle the workload of four nonprioritized buses. Furthermore, this priority has no adverse effect on the evacuation clearance time of nontransit evacuees. On the basis of this study, transit priority in a multimodal evacuation should be used.

Sustained Flow Index: Stochastic Measure of Freeway Performance

Research into the operation of traffic flow at high volumes reveals that the capacity of freeways is not a fixed number but is rather a random variable. Since traditional operational performance measures for the analysis of traffic flow on freeways typically disregard the randomness of capacity, new approaches to make use of the concept of randomness for freeway operation analysis are required. To address that need, this paper introduces a new indicator of freeway performance based solely on a stochastic approach to capacity computation. With this new indicator, the maximum reliable volume that can be carried by a freeway over prolonged time periods was derived from parameters of capacity distribution functions. The breakdown probability corresponding to the optimum volume can be used to select a single value from the capacity distribution function. To explore the empirical relationship between expected values of capacity and the optimum volumes calculated from this new computational process, flow data from several German freeway sections were analyzed. To illustrate the application potential for a sustained flow index, this paper also discusses the bases for increasing the effectiveness of ramp metering and vehicle routing management techniques.

Methodology for Simulating Manual Traffic Control

Manual traffic control (MTC) is a key part of managing traffic during emergencies and planned special events. Despite its long history, there has been little, if any, research on how to model MTC effectively. It is commonly represented as a version of actuated signal control. Although this method is useful, it has significant shortcomings because it does not adequately represent the variability of police officer control actions under field conditions. This paper presents the results of recent research to develop an MTC model and integrate it into a traffic simulation system. Here, the process of MTC is represented by police officers’ decision making in relation to a system of discrete choice equations (logit models) that compute signal phase length and green-time allocation as a function of demand, directional priority, phase length, and gaps in the approach traffic streams. The MTC discrete choice model was validated with the use of various data sets to show that it computed phase lengths and allocated green time within a 95% confidence level compared with field observation.

Unconventional Intersection Control Strategies for Urban Evacuation

Intersections form one of the biggest challenges to emergency managers when evacuation plans are developed in urban areas. Signalized intersections reduce the directional capacity of a roadway because they must allocate the right-of-way between competing movements and approaches. In response to this problem, a variety of unconventional intersection control strategies have been developed for implementation during evacuations. Three of the most common are manual traffic control (MTC), flashing yellow signals, and crossing elimination. Fundamentally, each of these strategies has demonstrated strengths and weaknesses, but little work has been done to evaluate them systematically in an apples-to-apples comparison. The goal of this study was to determine which unconventional intersection control strategy was best suited for a given urban evacuation scenario. With results generated by the microscopic traffic simulation software VISSIM 7.0, a dynamic program identified the optimum control strategy for various evacuation scenarios. One general finding of this research was that MTC was best suited for intersections immediately upstream of a bottleneck or for closely spaced, uncoordinated signals. Flashing yellow signals appeared to work well for intersections with high, unbalanced demand and low volumes on the minor approach. Crossing elimination strategies worked best when demand from nonconflicting directions was high and all other approach volumes were relatively low. In practice, these control strategies can be used in combination with other evacuation techniques such as zone phasing and contraflow to utilize network capacity better and to decrease clearance time.

Use of Nationwide Automatic Identification System Data to Quantify Resiliency of Marine Transportation Systems

This paper describes the approach and the results of an ongoing research effort to assess the resilience of port operations following major disasters and other disruptive events. The work presented in this paper used archival data from the U.S. Coast Guard’s nationwide automatic identification system to quantify the state of resiliency of coastal navigation systems. Illustrating the experimental methodology are case study examples that assess the disruptions that resulted from a collision in March 2014 in the Houston Ship Channel, Texas, and from Superstorm Sandy in 2012 on the greater Port of New York and New Jersey. The methods and results can be adapted and implemented for quantitatively evaluating levels of port activity following disruptive events and for a better understanding of the factors that lead to more resilient maritime systems.