Henry Brown

Effects of Access Control on Safety on Urban Arterial Streets

Access control techniques are used to improve traffic performance and safety on highways. One important benefit of access control is improved safety. For a quantitative assessment of the benefits of access control on safety, impact models are needed to predict crash frequencies based on the geometric and access control characteristics of the segments. The objective of this research was to develop regression models to predict crash frequencies on urban multilane arterial segments. To develop these models, data were collected on geometric and access control characteristics of the segments and the number of crashes on the segments by severity type. Negative binomial regression models were developed to predict the total number of crashes, number of property-damage-only crashes, and number of fatal and injury crashes. The three models have a similar structure. The exposure-to-risk variables include segment length, number of years, and annual average daily traffic. The significant factors include density of access points, proportion of signalized access points, presence of an outside shoulder, presence of a two-way left-turn lane, and presence of a median with no openings between signals. The results indicate that access control has a beneficial effect on safety.

A Tool for Evaluating Access Control on High Speed Urban Arterials, Part I

A highway system serves two needs: mobility and accessibility. Access control techniques are used to restrict access to the highway and improve vehicle flow. The objective of this research was to develop a comprehensive procedure to evaluate access control alternatives. The procedure includes the design and quantitative evaluation of alternatives to select the best one. Evaluation of each alternative includes prediction of turning volumes, delays, crash rates, and economic effectiveness. Several existing models predict traffic delays for signalized intersections and for minor streams at unsignalized intersections. Models are needed to predict delays of arterial streams caused by minor streams at unsignalized intersections. To address this missing component, models were developed to predict the delays caused to arterial streams by the following maneuvers: merging onto the arterial, diverging from the arterial, and left turn from the arterial. Models to predict crash rates for multi-lane arterial segments in Indiana based on geometric and access control characteristics were also developed. Models were developed to predict total, property-damage-only, and fatal/injury crashes. For the economic evaluation of each alternative, delays and stops are converted to operating costs for representative periods, and the crash rates are converted to crash costs. The agency costs can also be estimated. After the economic evaluation of each access control alternative, the best alternative can be selected. This volume, Part I, contains the research report, presenting the literature review, procedure to evaluate access control alternatives, the traffic delay models, the safety models, the economic evaluation of alternatives, implementation considerations, and a summary of the research findings.

Safety Evaluation of Diverging Diamond Interchanges in Missouri

The diverging diamond interchange (DDI) has gained in popularity since its first implementation in the United States in 2009. The operational benefits and lower costs of retrofitting a conventional diamond with a DDI have contributed to increased use of the DDI. Research on DDIs has focused primarily on the assessment of operational benefits. Formal safety evaluations of DDIs are lacking. This study aimed to fill the knowledge gap by conducting a safety evaluation of DDIs using three types of before–after evaluation methods: naive, empirical Bayes, and comparison group. Three evaluation methods were used because each involved different trade-offs, such as data required, complexity, and regression to the mean. All three methods showed that a DDI replacing a conventional diamond decreased crash frequency for all severities. The highest crash reduction (59.3% to 63.2%) was observed for fatal and injury crashes. Crashes involving property damage only were reduced by 33.9% to 44.8%. Total crash frequency also decreased by 40.8% to 47.9%. A collision diagram analysis revealed that the DDI, as compared with a diamond, traded high-severity crashes for lower-severity crashes. Whereas 34.3% of ramp terminal fatal and injury crashes in a diamond occurred in left-turn angle crashes with oncoming traffic, the DDI eliminated this crash type. One potential concern for the DDI is the possibility of wrong-way crashes, but only 4.8% of all fatal and injury crashes occurring at the ramp terminal of a DDI were wrong-way crashes. The DDI offers significant crash reduction benefits over conventional diamond interchanges.

Evaluation of Mobile Work Zone Alarm Systems

Highway maintenance often involves the use of mobile work zones for various types of low-speed moving operations, such as striping and sweeping. The speed differential between the moving operation and traffic and the increasing problem of distracted driving can lead to potential collisions between approaching vehicles and the moving work zone. One novel tool for mitigating this problem is a mobile work zone alarm system. This paper describes the field evaluation of two types of mobile work zone alarm devices: an alarm device and a directional audio system (DAS). Three modes of operation were tested: continuous, manual, and actuated. The components of the evaluation included sound level testing, analysis of merging distances and speeds, and observations of driving behavior. The sound levels for the tested configurations were within national noise standards. All tested configurations increased the merging distance of vehicles except for the alarm actuated setup. The DAS continuous setup also reduced vehicle merging speeds and the standard deviation of merging distance. Some undesirable driver behaviors were occasionally observed, but it was unclear whether these driver behaviors were caused by the presence of the mobile work zone alarm device. Factors such as horizontal and vertical curves and movement of the vehicle with the truck-mounted attenuator caused false alarms and false negatives. The research demonstrated that mobile work zone alarms have the potential to be an effective tool in improving safety. Further refinements to the systems could improve effectiveness.

Investigation of Alternative Bicycle Pavement Markings with the Use of a Bicycle Simulator

The past decade has seen increased public interest in sustainable transportation modes in the United States. However, there is a relative lack of guidance regarding standards and specifications for bicycle facilities compared with the highway mode. This project sought to address this deficiency through the investigation of alternative pavement markings for bicycle wayfinding and proper bicycle placement at signalized intersections as part of the federal Nonmotorized Transportation Pilot Program in Columbia, Missouri. This evaluation was accomplished with a bicycle simulator study and postsimulator survey with 27 participants. A network of 37 intersections with characteristics similar to intersections in Columbia was created with the ZouSim simulator. The survey included questions regarding bicycling habits and preferences for the alternative markings. For wayfinding, two alternative types of pavement markings and the signage recommended by the Manual on Uniform Traffic Control Devices (MUTCD) were evaluated. Both the survey and the simulator results indicated that the Type 2 wayfinding markings with a green circle performed better with respect to visibility and delineating the bicycle route. The bicycle placement portion of the study investigated three alternative types of markings as well as the MUTCD markings and signage to help riders position their bicycle at the correct location to receive a green signal. The bicycle placement results indicated that the Type 1 and Type 2 experimental detector markings resulted in the fewest number of missed detections, while the Type 1 marking was the preferred alternative of the survey participants.

Traffic Flow Modeling of Diverse Work Zone Activities

What effect does work activity type have on traffic conditions in a work zone? This question has still not been answered satisfactorily in practice. Without knowing the true effect a work activity has on traffic, practitioners are forced to make assumptions while scheduling work. This paper attempts to answer this question by studying the traffic flow characteristics, that is, traffic speed versus flow curves, capacity reduction factors, and free-flow speed reduction factors, for various activities related to construction and maintenance. The importance of the speed–flow curves and reduction factors for work zone planning is also stressed in the latest edition of the Transportation Research Board’s Highway Capacity Manual. This manual recommends capacity and speed reduction factors for work zones, yet does not include specific guidance for including the impact of work activities. Thre e traffic stream models, Gipps, Newell–Franklin, and Van Aerde, were calibrated using field data from St. Louis, Missouri. The Van Aerde model fitted the field data the best as compared to the other two models. Using the Van Aerde model-generated speed–flow curves, it was found that the capacity for bridge-related activities varied from 1,416 vehicles per hour per lane (vphpl) to 1,656 vphpl and for pavement-related activities from 1,120 vphpl to 1,728 vphpl. The capacity reduction factor for different work activities was found to be in the range 0.68 to 0.95, whereas the free-flow speed reduction factor was found to be in the range 0.78 to 1.0. The methodology proposed in this paper contributes toward the development of practitioner guidance and incorporation of work activity effects into traffic impact assessment tools.

Maintenance of Traffic for Innovative Geometric Design Work Zones

In an effort to improve the safety and capacity of existing roads, many transportation practitioners are implementing innovative designs at intersections and interchanges. The development of construction phasing plans for these projects is a critical component for maintaining safety and mobility on the facility during construction. The goal of this study was to address the gaps in existing knowledge by presenting the state of the practice and providing guidance for transportation practitioners in developing construction phasing and maintenance of traffic (MOT) plans for projects with innovative geometric designs. Several types of innovative geometric designs were studied, including the round about, single-point urban interchange, diverging diamond interchange, restricted-crossing left turn, median U-turn, and displaced left turn. Examples of MOT phasing diagrams showing phasing sequencing and construction work areas were developed on the basis of a review of the literature, a survey of practitioners, interviews with industry experts, and a review of actual project plans. The examples of MOT phasing diagrams are intended to serve as a starting point for transportation practitioners, but project-specific factors such as driver experience, availability of detours, traffic counts, adjacent land use, elevation differences, barrier offsets, number of lanes, and anticipated impacts of a possible closure should be considered when deciding on the best MOT methods for a given project.

Decision Methodology for Temperature Control of Pavements

About 2.5 million miles of paved roads, which would cover an area about the size of the state of Georgia, exist in the United States. Pavements accumulate and dissipate solar energy in daily cycles. The increased heat in the pavement has many detrimental effects, including the accelerated degradation of the pavement, which results in increased costs to departments of transportation, and urban warming, which results in increased costs for cooling nearby inhabited structures and possibly contributes to microclimate change. Techniques such as heat exchangers that capture heat energy and transfer it to other forms of energy can reduce the extreme temperatures in pavements. Laboratory and some small-scale field trials of these systems have been conducted; however, the technology has not received wide implementation to date. Challenges to such implementation include limited documentation on the effectiveness of pavement cooling, a lack of accepted standard designs, a lack of evidence of long-term performance, the need for more efficient heat exchangers, and the cost of the system. Technological developments are rapidly overcoming the challenges, and the potential benefits of energy recovery are significant and include extended pavement life, reduced energy consumption in areas surrounding the pavement, improved air quality, the production of energy that could be used for other applications, and reduced microclimate impacts. This paper presents a decision methodology that would help designers and stakeholders evaluate, in terms of performance and cost measures, alternatives for systems to control pavement temperatures.

A TOOL FOR EVALUATING ACCESS CONTROL ON HIGH-SPEED URBAN ARTERIALS. PART II: USER'S GUIDE

A highway system serves two needs: mobility and accessibility. Access control techniques are used to restrict access to the highway and improve vehicle flow. the objective of this research was to develop a comprehensive procedure to evaluate access control alternatives. The procedure includes the design and quantitative evaluation of alternatives to select the best one. Evaluation of each alternative includes prediction of turning volumes, delays, crash rates, and economic effectiveness. Several existing models predict traffic delays for signalized intersections and for minor streams at unsignalized intersections. Models are needed to predict delays of arterial streams caused by minor streams at unsignalized intersections. To address this missing component, models were developed to predict the delays caused to arterial streams by the following maneuvers: merging onto the arterial, diverging from the arterial, and left turn from the arterial. Models to predict crash rates for multi-lane arterial segments in Indiana based on geometric and access control characteristics were also developed. Models were developed to predict total, property-damage-only, and fatal/injury crashes. For the economic evaluation of each alternative, delays and stops are converted to operating costs for representative periods, and the crash rates are converted to crash costs. The agency costs can also be estimated. After the economic evaluation of each access control alternative, the best alternative can be selected. This volume, Part II, describes the procedure to evaluate access control alternatives. In addition, computer tools that could facilitate the evaluation process are also discussed.