Guide for Quantitative Approaches to Systemic Safety Analysis (2020)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

88 Summary of the Systemic Safety Management Approach For years, highway agencies have focused on identifying high-crash locations and making safety improvements at these sites. This crash-history-based (or hot-spot) approach to safety management has several disadvantages. In particular, crashes must occur at a site before an improvement is made; safety improvements may be made at sites to remedy specific crash types that might not occur again, even if no improvement were made; and crash types that occur frequently but are dispersed across the network may not be effectively addressed. In recent years, several highway agencies have been implementing a systemic safety management approach to complement their crash-history-based safety management approach. The systemic safety management approach focuses on implementing proven, low-cost safety improvements at a large number of sites across the network with a high potential for future target crashes. The primary advantages of the systemic safety management approach are that (a) it can be used in the absence of high-quality crash data, (b) countermeasures can be programmed for imple- mentation at locations that may not have a history of crashes, (c) crash types that occur with high frequency but are dispersed across the network can be remedied, and (d) the data-driven approach is adaptable based on available data. One of the primary distinguishing factors between the crash-history-based and systemic safety management approaches is that with the crash-history-based safety management approach, the focus is on identifying and remedying sites where a high frequency of crashes occurred, and it does not matter that at one site one crash type occurred most frequently and at another site another crash type occurred most frequently. For the crash-history-based safety management approach, as long as a site was identified as having a high frequency of crashes, the site would be identified for potential improvement and a treatment would be tailored to address the specific crash patterns and site conditions. On the other hand, for systemic safety, the overall process starts by identifying a target crash type(s) to be addressed. Target crash types to be addressed could be identified based on a systemwide analysis of an agency’s crash data or referenced in a state or regional safety plan. Common crash types that agencies have addressed using a systemic safety management approach include: • Lane departure, • Rollover, • Fixed object, • Head on, • Angle, • Speed related, • Younger driver involvement, • Impaired driving, • Pedestrians, • Bicyclists, and • Nighttime. S E C T I O N 6

Summary of the Systemic Safety Management Approach 89 In conjunction, several facility types that agencies have focused on using systemic safety management approaches to address target crash types include: • Rural freeways, • Rural multilane highways, • Rural two-lane roads, • Rural local roads, • Rural roads with pavement width less than 24 ft, • Horizontal curves on rural two-lane roads, • Low-volume local roads, • Unpaved roads, and • Signalized and stop-controlled intersections. Types of countermeasures that agencies have implemented as part of their systemic safety management projects include: • Roadway segments: – Rumble strips (both shoulder and centerline), – Cable median barrier, – SafetyEdge, – High-friction surface treatments, – Enhanced pavement markings, – Curve warning signs, – Chevrons/delineators, – Lane/shoulder widening, – Speed feedback signs, and – Tree/clear zone removal. • Intersections: – Signal backplates, – Crosswalk enhancements—striping, signing, rectangular rapid flashing beacons, – Countdown pedestrian signals, – Pedestrian refuge islands, – Curb extensions, – Reflective strips on sign posts, – Mini-roundabouts, and – Lighting. Highway agencies have basically used three approaches to implementing systemic safety management: application of the FHWA Systemic Tool methodology, application of SPFs using in-house tools, and application of the usRAP methodology using the associated ViDA software. The systemic safety management approach described in the FHWA Systemic Tool is the least complex of the three types of applications and is the most adaptable for agencies with incom- plete or poor quality inventory, traffic volume, and/or crash data. The key with this application, after identifying a target crash type and facility type to address, is to initially identify potential contributing factors based on data that are available for every site considered in the analysis. In this way, a simple yet data-driven systemic analytical or methodological approach can be developed based on available data. Then, priorities can be established for incrementally collecting, over time, additional data elements and developing a more comprehensive and reliable dataset of site characteristics corresponding to potential contributing factors. As more reliable data become available, the systemic analytical or methodological approach can evolve and become more robust. With the publication of the HSM and its procedures becoming accepted as reliable best practice, more agencies are interested in developing their own SPFs or calibrating existing SPFs

90 Guide for Quantitative Approaches to Systemic Safety Analysis to their local conditions. SPF development, however, requires a special skill set which many state and local highway agencies do not have within their organizations, so agencies often look to hire universities and/or consultants with the technical expertise to develop agency-specific SPFs and in-house tools for data management and network screening. Application of a systemic safety management approach using SPFs requires high-quality, robust roadway inventory, traffic volume, and crash datasets for all roads within an agency’s jurisdiction, or at least for the roadways an agency is interested in managing. This data require- ment may keep agencies from utilizing SPFs for systemic application. The most direct and comprehensive existing software that implements a systemic safety management approach using SPFs is the AASHTOWare Safety Analyst software. Safety Analyst can be used to implement both the crash-history-based and the systemic safety management approaches. Only a few states with Safety Analyst licenses have limited experience using the systemic site selection module since this functionality was only recently added to the software. Utilizing an existing software, such as Safety Analyst, requires an agency to make a commitment to map and import its data into the software. To do so, an agency should make use of available data and focus on a portion of its network and, over time, develop a more comprehensive dataset for use with the software. This may mean that the full functionality or capabilities of software such as Safety Analyst are not initially realized but could be later expanded. Application of the usRAP methodology and associated ViDA software is unique in that it is a more defined methodological approach to systemic safety, but again, it can be adapted for use within the context of an agency’s needs. Also, having tools available to develop the required datasets makes this approach appealing, although to implement this approach across a wide network likely requires some level of automation to collect at least a portion of the required data elements. As more agencies are potentially interested in implementing systemic safety management programs, interest in evaluating the effectiveness of the programs increases. Common evaluation approaches such as a trend analysis, a simple before-after study approach, a shift of proportions method, and the EB before-after study method can be conducted. The results can be commu- nicated in an appropriate manner to meet the needs of the target audience and to inform future decision making to maximize the effectiveness of an agency’s safety program in an effort to achieve its goals.