Transportation safety modeling and evaluation : alternative geometric designs, enforcement, and airfield applications /

A top priority of transportation agencies in the United States is to improve safety of transportation facilities through the use of latest technology, innovative designs, procedural methods, and training practices to decrease fatalities, injuries, and property damage. In order to continue improving roadway safety, different approaches such as alternative designs have been considered. Alternative designs for roadway facilities include J-turn for minor roads and high-speed expressway intersections, the Diverging Diamond Interchange (DDI) for freeway interchanges, or red light cameras for signalized intersections. There is limited research evaluating the safety effectiveness of recently implemented alternative designs and enforcement strategies. This dissertation focused on developing jurisdiction specific crash prediction models, calibrating existing models, and applying rigorous statistical methods to study the safety effectiveness of these new alternative treatments. This dissertation found that the DDI design replacing a conventional diamond decreased crash frequency for all severities. Fatal and injury (FI) crashes experienced a 62.6 percent reduction. Property damage only (PDO) crashes reduced by 35.1 percent and total (TOT) crashes decreased by 47.9 percent. The collision diagram analysis of the DDI showed that the top two crash types were: 1) rear end collisions between right turning movements on the exit ramp at the intersection, and 2) rear end collisions on the outside crossroad approach leg to the ramp terminal. The DDI design traded a severe crash type, right angle left turn crash, with less severe rear end, sideswipe, and loss of control crash types. Wrong way crashes inside the crossroad between ramp terminals accounted for 4.8 percent of the FI crashes occurring at the DDI. This dissertation also examined the DDI safety effect on two adjacent facilities: speed change lanes and major signalized intersections. There is no strong evidence that DDIs impacted the safety of adjacent roadway facilities, either positively or negatively. Another alternative intersection design studied in this dissertation was the J-turn intersection. The safety evaluation of the implementation of the J-turn replacing two-way stopcontrolled intersections was effective at decreasing FI crashes by 63.8 percent and TOT crashes by 31.2 percent. The collision diagram analysis showed that the most recurrent crashes were sideswipe with 31.6 percent and rear end with 28.1 percent on the main road. Red light running was also evaluated in this dissertation. The implementation of red light running cameras in Missouri resulted in a reduction of FI crashes by 7.4 percent and increase in PDO crashes by 3.8 percent. Additionally, right angle crashes were reduced across all severities, including 14.5 percent for FI crashes. Rear end crashes increased by 16.5 percent overall. The crash cost benefit results showed a positive net economic benefit of $35,269 per site per year in 2001 dollars (approximately$47,000 in 2015 dollars). It translated into an overall 5.0 percent economic crash cost benefit. In addition to roadway safety, this dissertation also evaluated airfield safety. In the field of aviation, runway incursions are the incorrect presence of and aircraft, vehicle or person on an active runway designated for takeoff and landing. Runway incursions can result in property damage or loss of life through incidents leading to aircraft collisions or avoidance maneuvers. Efforts are on the rise to reduce the risk of runway incursions at airports. However, guidance is mostly qualitative and does not provide specific quantitative measures to predict runway incursion frequency and evaluate the effectiveness of treatments. This dissertation adapted statistical roadway safety modeling to airport airfield operations. The transferability of roadway safety modeling theory was possible because airfield operations share similar measures of exposure and hazard concepts. Thus, models were developed to estimate runway incursion frequency for hub airports in the United States. Assessing runway incursion frequency and treatment effectiveness with quantitative measures enables a more straightforward comparison of different facilities, alternatives, and treatments. The models developed in this dissertation contribute to decision making and the implementation of cost effective countermeasures to mitigate runway incursions.Dr. Praveen Edara, Dissertation Supervisor.Includes bibliographical references (pages 173-180)

Statistical and simulation methods for evaluating stationary and mobile work zone impacts

In 2014, nearly 10% of overall congestion on freeways was due to the presence of work zones (WZs), equivalent to 310 million gallons of fuel loss (FHWA, 2017a). In terms of safety, in the US, every 5.4 minutes, a WZ related crash occurred in 2015 (96,626 crashes annually) (FHWA, 2017b). Maintenance work involves both Stationary Work Zones (SWZs) and Mobile Work Zones (MWZs). There are many analytical and simulation-based tools available for analyzing the traffic impacts of SWZs. However, the existing traffic analysis tools are not designed to appropriately model MWZs traffic impacts. This study seeks to address this gap in existing knowledge through the use of data from MWZs to develop and calibrate traffic impact analysis tools. This objective is accomplished through data fusion from multiple sources of MWZ, probe vehicle and traffic detector data. The simulation tool VISSIM is calibrated for MWZs using information extracted from videos of MWZ operations. This is the first study that calibrated the simulation based on real driving behavior behind a MWZ. The three recommended calibration parameters are safety reduction factor of 0.7, minimum look ahead distance of 500 feet and the use of smooth closeup option. These calibration values can be used to compare MWZ scenarios. Also, the data collection framework and calibration methodology designed in this study could be used in future research. The operational analysis concluded that a moving work activity lasting one hour or more are suggested to be done when traffic volumes are under 1400 veh/hr/ln, and preferably under 1000 veh/hr/ln, due to the drastic increase in the number of conflicts. In addition, three data driven models were developed to predict traffic speed inside a MWZ: a linear regression model and two models that used Multi-Gene Genetic Programming (MGGP). The second objective is to develop models and tools for safety assessment of stationary work zones. In the WZ safety literature, few studies have quantified the safety impact of SWZ and almost no quantitative study assessing MWZ safety impact. Using Missouri data, this study introduces 20 new crash prediction models for SWZs on freeways, expressways, rural two lane highways, urban multi-lane highways, arterials, ramps, signalized intersections, and unsignalized intersections. All the models except freeway SWZs are proposed for the first time in the literature. The mentioned SWZ models are implemented in a user-friendly spreadsheet tool which automatically selects the most appropriate model based on user input. The tool predicts crashes by severity, and computes the crash costs. For MWZs, there is no crash data available to develop crash prediction models. Thus, this dissertation analyzed conflict measures as a surrogate for safety impacts of MWZs. Conflict measures were generated from the trajectories of traffic simulation model. The safety trade-off plots between conflicts and combination of MWZ's duration and traffic volume were introduced. A transportation agency can use these plots to determine, for example, if they should conduct a MWZ for a short duration when the volume is high or for a longer duration when the volume is lower.Includes bibliographical reference

Benefits of Advanced Traffic Management Solutions: Before and After Crash Analysis for Deployment of a Variable Advisory Speed Limit System

Variable speed limit (VSL) systems are important active traffic management tools that are being deployed across the U.S. and indeed around the world for relieving congestion and improving safety. Oregon’s first variable advisory speed limit signs were activated along Oregon Highway 217 in the summer of 2014. The variable advisory speed system is responsive to both congestion and weather conditions. This seven-mile corridor stretches around Western Portland and has suffered from high crash rates and peak period congestion in the past. VSL systems are often deployed to address safety, mobility and sustainability related performance. This research seeks to determine whether the newly implemented variable advisory speed limit system has had measurable impacts on traffic safety and what the scale of the impact has been. The research utilizes a before-after crash analysis with three years of data prior to implementation and around 16 months after. Statistical analysis using an Empirical Bayes (EB) approach will aim to separate the direct impacts of the variable advisory speed limit signs from the long term trends on the highway. In addition, the analysis corrects for the changes in traffic volumes over the study period. Three data sources will be utilized including Washington County 911 call data, Oregon incident reports, and official Oregon Department of Transportation crash data reports. The analysis results are compared between data sources to determine the reliability of 911 call data as a proxy for crash statistics. The conclusions should be able to provide an indication of whether variable advisory speed limits can provide increased safety along high crash corridors

STANDARDIZING AND SIMPLIFYING SAFETY SERVICE PATROL BENEFIT-COST RATIO ESTIMATION

Safety Service Patrol (SSP) programs operate nationwide with the aim of mitigating the impact of traffic incidents, especially along urban freeways. The central mission of the SPP programs is to reduce incident duration thereby reducing congestion related travel delays, fuel consumption, emission pollutants, and the likelihood of secondary incidents. The SSP-BC Tool was developed herein to fill the need for a standardized benefit-cost ratio estimation methodology for SSP programs with wide applicability and substantiated and needed updatable monetary conversion rates. The developed tool is designed to capture characteristics of incident, traffic, roadway geometry, and weather particular to the state area. VISSIM, a traffic microsimulation platform, was used to develop several multiple regression models with R-square values of 0.7 to 0.9 to assess the impact of travel delay, fuel consumption, and emission pollutants. Separate approaches were employed to estimate the savings in secondary incidents. In addition, a comprehensive method to compute fuel consumption and emissions is presented

High-Speed Rail: The Wrong Road for America

In the face of high energy prices and concerns about global warming, environmentalists and planners offer high-speed rail as an environmentally friendly alternative to driving and air travel. California, Florida, the Midwest, and other parts of the country are actively considering specific high-speed rail plans. Close scrutiny of these plans reveals that they do not live up to the hype. As attractive as 110-to 220-mile-per-hour trains might sound, even the most optimistic forecasts predict they will take few cars off the road. At best, they will replace for profit private commuter airlines with heavily subsidized public rail systems that are likely to require continued subsidies far into the future. Nor are high-speed rail lines particularly environmentally friendly. Planners have predicted that a proposed line in Florida would use more energy and emit more of some pollutants than all of the cars it would take off the road. California planners forecast that high-speed rail would reduce pollutionand greenhouse gas emissions by amere 0.7 to 1.5 percent -- but only if ridership reached the high end of projected levels. Lower ridership would nullify energy savings and pollution reductions. These assessments are confirmed by the actual experience of high-speed rail lines in Japan and Europe. Since Japan introduced high-speed bullet trains, passenger rail has lost more than half its market share to the automobile. Since Italy, France, and other European countries opened their high-speed rail lines, rail's market share in Europe has dwindled from 8.2 to 5.8 percent of travel. If high-speed rail doesn't work in Japan and Europe, how can it work in the United States? As megaprojects -- the California high-speed rail is projected to cost $33 to$37 billion -- high-speed rail plans pose serious risks for taxpayers. Costs of recent rail projects in Denver and Seattle are running 60 to 100 percent above projections. Once construction begins, politicians will feel obligated to throw good taxpayers' money after bad. Once projects are completed , most plans call for them to be turned over to private companies that will keep any operational profits,while taxpayers will remain vulnerable if the trains lose money. In short, high-speed rail proposals are high cost, high-risk megaprojects that promise little or no congestion relief, energy savings, or other environmental benefits. Taxpayers and politicians should be wary of any transportation projects that cannot be paid for out of user fees

Synthesis of Practices for Mitigating the Impact of Work Zones on Traffic

Mobility and safety through work zones has become a prominent issue in work zone planning because motorists commonly expect minimal disruption to their normal driving habits. However, work zones can create unacceptable delays and queues if not adequately addressed. State transportation agencies (STAs) are currently working towards meeting the requirements of the Federal Highway Administration’s Work Zone Safety and Mobility Rule, 23 CFR, Part 630. This rule requires STAs to systematically manage the impacts of work zones on federal-aid highways and other projects that have significant impact on road users. STAs therefore use various congestion mitigation strategies in their transportation management plans. This synthesis identifies and discusses many frequently used strategies and many strategies that are relatively new to several agencies. When developing transportation management plans, a well-rounded and comprehensive group of strategies can be made to work together to mitigate work zone congestion to levels that are acceptable to motorists. This synthesis thus provides a tool for STAs to use in the work zone planning stages of a project

Traffic Impact Assessment of Moving Work Zone Operations, October 2017

Road maintenance activities involve both short-term stationary work zones and moving work zones. Moving work zones typically involve striping, sweeping, pothole filling, shoulder repairs, and other quick maintenance activities. Existing traffic analysis tools for work zone scheduling are not designed to model moving work zones. A review of existing literature showed that many of the existing studies of moving bottlenecks are theoretical in nature, limited to certain lane configurations, and restrictive in the types of mobile work zone attributes considered. This research project sought to address this gap in existing knowledge by using field data from moving work zones to develop and calibrate a traffic impact analysis tool. This objective was accomplished through the fusion of multiple sources of work zone and traffic data. Four different data sources were used: Missouri Department of Transportation (MoDOT) electronic alerts, probe-based travel times, data from point detectors, and field videos of moving work zones recorded from the back of a truck-mounted attenuator. A linear regression model was developed to predict traffic speed inside a moving work zone. Predictor variables in the models included historical speed, number of lanes, type of lane closure, and time of day. The simulation tool VISSIM was calibrated for moving work zones using information extracted from videos of moving work zone operations. The three recommended calibration parameters are a safety reduction factor of 0.7, a minimum look ahead distance of 500 ft, and the use of a smooth closeup option. These calibration values can be used by departments of transportation to model moving work zone scenarios. The operational analysis concluded that a moving work activity lasting one hour or more operates best when traffic volumes are under 1,400 veh/hr/ln, and preferably under 1,000 veh/hr/ln. Further, scheduling shorter duration moving activities on high-volume roads at multiple times (on the same day or on different days) works better than scheduling a longer duration activity. The safety analysis generated trade off plots between the number of conflicts and combinations of activity duration and traffic volume. A DOT can use these plots to determine, for example, if it should conduct a moving work activity for a short duration when the volume is high or for a longer duration when the volume is lower

Best Practices for Performance Measurement in Transportation Operations and Maintenance

Public agencies benefit from measuring their performance as it helps to focus employee and organizational activities. State departments of transportation have become more performance-oriented over the past two decades and routinely collect data on highway safety, infrastructure condition, system operations, project delivery, winter maintenance, transit, bicycle and pedestrian facilities, and customer service. While the Kentucky Transportation Cabinet (KYTC) use performance measures in a variety of areas, the agency wants to adopt new metrics related to mobility and the responsiveness of maintenance operations. This report documents performance measurement strategies used at state transportation agencies throughout the country and proposes new performance measures in these areas for KYTC. Among the performance measures put forward to the Cabinet, the following ones ranked most highly: (1) response times for complaints and potholes, (2) contract response time, (3) percentage of time and money spent on routine and emergency maintenance of drainage, guardrail, and cable median barriers, (4) response time to repair guardrail and cable median barriers, and (5) winter maintenance operations. As KYTC further integrates performance measures into its operations, it is critical to clearly communicate performance information to the public using tools such as online dashboards and reports

Effectiveness of extra enforcement in construction and maintenance work zones

As traffic-related work zone crashes continue to increase across the nation, safety of road users and workers has become a top priority for transportation agencies. Since inattention and irresponsible behavior by drivers are surmised to contribute to the frequency of work zone crashes, a program featuring extraordinary presence of and enforcement by law officers has been implemented in many states to address this concern. A literature search of such programs and related research was conducted. While the overall benefits of these activities have been found positive, much of the evidence has been anecdotal. To assess the scope of extra work zone enforcement programs, a survey was developed and distributed to state departments of transportation across the nation. This survey sought information regarding these efforts such as criteria for selection of target work zones, methods of enforcement operations, and beneficial results. A special survey was also designed and distributed to enforcement agencies in Iowa and other selected states. In addition to the surveys, personal contacts and office visits were conducted by the research team staff. The study found that use of extra enforcement in work zones is a common practice in many states and these activities appear to be increasing. Current literature, survey responses, and interviews have all indicated a prevalent opinion for the benefits of increased law enforcement presence and activity in work zones. Very few comments offered conclusions of negative impacts, such as additional congestion, from these efforts. However, the beneficial effects of focused enforcement have not been intensively quantified. In addition, procedures for the use of law officers in work zones are quite inconsistent across the nation, as is the general implementation of specific legislation addressing work zone traffic violations. Similar variation can be found in funding levels and sources for enforcement activities in work zones among the states. Training of law officers prior to work zone duty does not appear to be commonly required, though the value of focused training is being recognized in some states. As crashes and deaths continue to rise annually in our nation\u27s work zones, it is imperative that demonstrated beneficial programs such as the expanded use of law officers in these locations be continued, refined, and expanded. Future study is needed to supplement the knowledge base and provide guidance to agencies when considering the use of law enforcement to calm traffic, ensure compliance with traffic laws, and thus provide for safer work zones