Safety Evaluation of Access Management Policies and Techniques

Transportation Research Record, 2018

The Access Management Manual, Second Edition defines access management as "the coordinated planning, regulation, and design of access between roadways and land development. It encompasses a range of access management alternatives that promote the efficient and safe movement of people and goods by reducing conflicts on the roadway system and at its interface with other modes of travel. These access management alternatives include improvements to benefit transit, pedestrians, and bicyclist, as well as different treatments for urban, suburban, and rural settings" (1). One of the challenges with access management-related studies has been the availability of necessary data for conducting such studies. The Utah Department of Transportation (UDOT) began a light detection and ranging (LiDAR) data inventory in 2012 that includes access locations along all segments of the UDOT roadway network. The LiDAR inventory was repeated in 2014 and 2015. Combined with UDOT's crash data, the availability of access point data allowed an in-depth safety-related study to find relationships among access density, access management alternatives, and crash occurrences (2). Safety impacts of access management alternatives can be analyzed using before-and-after studies. However, in a traditional safety impact analysis it is necessary to install an access management alternative in the field and a few years must pass to accumulate reliable crash data. This is a timeconsuming study and there remains uncertainty in the crash data as a result of the random nature of crash occurrences. To circumvent the use of crash data a method called a conflict analysis was developed, which is performed typically in the field. Although this method is free from the issues pertinent to crash data, it still requires time and cost because the safety improvement measure must be installed at the study site. The surrogate safety assessment model (SSAM) was developed in an attempt to ameliorate the issues related to safety impact evaluation described above. With this method, a planned access management alternative is simply added to the simulation model and no physical installation of the alternative is needed. Thus, it requires less time and less cost. In this study, SSAM was tested to determine whether it could be used to evaluate safety impacts of access management alternatives, specifically a two-way left-turn lane (TWLTL) and a raised median. This paper presents a brief 773505T RRXXX10.

2020

Access management, defined in the Transportation Research Board Access Management Manual as "the systematic control of the location, spacing, design, and operation of driveways, median openings, interchanges, and street connections to a roadway," has been shown to have a positive impact on roadway safety. Numerous studies have been conducted on the safety relationship of access management techniques as a function of access spacing, corner clearance, and medians. Several of these studies have been conducted in the United States, including studies completed in the state of Utah. The results of research performed at Brigham Young University for the Utah Department of Transportation are highlighted in this paper. Specific research includes raised median safety impacts from both a traditional analysis methodology and using Bayesian methods, as well as an analysis of access management techniques (e.g., corner clearance, access spacing, median openings, left-turn lanes, etc.) at ...

Traffic safety and operations are important factors in transportation systems. Signalized intersections are of particular concern in terms of both safety and operation as they are designated to facilitate safe and efficient movement of conflicting traffic, oftentimes at high speeds. When accesses are located within the functional areas of major-arterial crossroads, additional conflicts arise from entering and exiting movements at the accesses, further complicating intersection activity. To help in understanding the effect of accesses in the vicinity of major-arterial crossroads, research was conducted on the impact of accesses on crashes within major-arterial crossroad functional areas. To understand the relationships within the functional areas, 144 signalized major-arterial crossroads across the state of Utah were examined. Frequency, type, and severity of functional area crashes as well as the intersection and roadway characteristics within the functional area were summarized in a database and analyzed to determine the influence of accesses on crashes within the functional area of intersections. Statistical analyses showed that the existence of accesses within the functional areas was related to an increase in the total number of crashes and the severity of such crashes. The analyses also showed that study intersections designed to meet state of Utah access management corner clearance standards exhibited fewer right-angle crashes and decreased crash severity. This research helps to identify the safety effects of access management treatments in the vicinity of major-arterial crossroads that can be used by governing agencies to help justify standards and identify safety benefits of access management.

Access Management Theories and Practices, 2015

Access management involves control, planning, and coordination of access along roadways to provide safe and efficient operation of transportation networks. According to existing literature, reducing conflict points and improving traffic safety are the main goals of access management techniques. Increase in traffic volumes and rapid growth of roadway networks have made these efficient techniques as a crucial part of roadway planning and design process. Some of the access management techniques employed in the recently published Highway Safety Manual (HSM) include: median treatments, traffic signal spacing, auxiliary lanes, corner clearances, driveways, U-turns as alternatives to direct left-turns, and frontage roads. Moreover, the Crash Modification Factors (CMFs) of these techniques, as estimators of the actual safety effect of countermeasures, are utilized in the HSM predictive methods to approximate the potential changes in crash frequency and severity after treatment implementation. The results of this study provide transportation agencies, practitioners, and decision-makers with a better understanding of how the HSM methods quantify the safety effects of access management techniques on different roadways. This is accomplished by providing output in the form of tabulated ranking of the impact of access management parameters for three roadway facilities defined in the HSM using the graphical method of sensitivity analysis.

2005

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by ...

2007

Access management involves the control, planning, and coordination of accesses along roadways for the purpose of providing safe and efficient operation of transportation networks. Reducing conflict points and promoting traffic capacity are the main goals of access management techniques (1). Increase of traffic volumes and rapid growth of roadway networks have made efficient access management techniques a crucial part of roadway design. Some of the access management techniques used in the recent Highway Safety Manual (HSM) include: median treatments, traffic signal spacing, right and left turn lanes, corner clearance, driveways, U-turns as alternatives to direct left-turns, and frontage roads. "Crash modification factors (CMFs)", used in the predictive methods in the HSM, are used to estimate the potential change in crash frequency and severity after implementation. This study investigates the CMFs of access management techniques in the HSM. Reliability of these techniques, sensitivity analysis, and the effect of each parameter are investigated.

2002

The Florida intrastate highway system (FIHS) is the network of state roads intended to carry the bulk of the state's high-speed and highvolume traffic movements. Comprising only 3% of the state's roads, the FIHS carries 32% of all traffic and 70% of truck traffic on the state highway system. However, the safe and efficient operation of the FIHS is in jeopardy. The system faces ever increasing levels of congestion and delay and a projected 20-year shortfall of $29 billion for needed capacity improvements. Given the lack of funding for needed capacity improvements, the Florida Department of Transportation (DOT) is turning to alternative strategies to preserve the operational integrity and safety of the system. Among these strategies is access management. The application of access management techniques on the FIHS is complicated, and sometimes undermined, by the separation of land use decision-making authority (controlled by local governments) and roadway decision-making authority (controlled by Florida DOT). To improve access management decision making on the FIHS, Florida DOT has begun to explain the overall benefits of access management to local governments and to coordinate the land development and roadway decision-making processes. Summarized is an effort to improve access management decision-making practices on a 10-mi corridor of US-19 in rural Levy County, an important north-south component of the FIHS.

This paper reviews the many research studies that relate traffic safety to access spacing, presents results of specially conducted analyses of accident information obtained from eight states, and sets forth emergent guidelines for assessing safety impacts of access spacing. The literature review and safety analyses were performed as part of NCHRP Project 3-52, Impacts of Access Management Techniques. Accident rate indices, derived from the literature synthesis and safety analyses, show the relative increase in accidents that can be expected as the total driveway density in both directions increases. These indices suggest that doubling the access frequency from 10 to 20 access points per mile would increase accident rates by 40 percent. A road with 60 access points per mile would have triple the accident rate (200 percent increase) as compared with a spacing of 10 access points per mile. Each additional access point increases the accident rate by about 4 percent. The research results suggest a generally consistent relationship-the greater the frequency of driveways and intersections, the greater the number of accidents. While the specific relationships reflect variations in road geometry, travel speeds, and driveway and intersection volumes, the general relationship remains consistent. The access spacing implications are clear. Increasing the spacing between access points helps reduce the number and variety of events to which drivers must respond. In addition, wide access spacing gives drivers more time for perception, reaction and navigation.

ICTIS 2011, 2011

Signalized intersections next to each other spatially on the same arterial share some unobservable information such as traffic flow and roadway characteristics, thus this study is to investigate the impact of access management techniques on crash counts at signalized intersections where the unobservable information is considered by developing panel data crash count data models based on crash data from 300 signalized intersections in Southern Nevada. Panel data random-effect model was selected to take into account the unobserved factors for each unique arterial. It was showed that Negative Binomial regression models were better able to reflect the dispersion in the crash data. Therefore, the random-effect negative binomial model (RENB) was applied to investigate the relationship between crash occurrence and access management techniques. The results showed that five variables significantly affected the safety at signalized intersections. The average length of corner clearance had negative impact on intersection crash occurrence while the total traffic flow in all directions, land use types, the number of lanes for minor streets and posted speed limit on minor streets were positively related to crashes at signalized intersections.