Roadway Cross-Section Reallocation: A Guide (2023)

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2-1   C H A P T E R 2 Decision-Making Principles Determining the appropriate use of street space depends on a community’s goals, the surround- ing land-use context, and the street’s role in the transportation system. The cross-section Decision- Making Framework presents a process for developing cross sections based on community priorities, mobility needs, and transportation safety. This process is founded on the following key principles: • Prioritize safety: The core principle of the framework is that cross sections must be designed to provide safety. The framework identifies context-specific minimum safe widths and separa- tion elements for vehicle lanes, bike lanes, bus lanes, sidewalks, and curbside uses. • Simplify decisions: The framework is simple and user-friendly. It distills the complex and dynamic relationships between street design and outcomes into manageable decisions. • Estimate outcomes: The framework discusses the environmental, social, and economic out- comes for each cross-section alternative. • Make decision-making transparent: The framework acknowledges that every decision is a choice, that tradeoffs are often necessary, and that communities deserve to know how various considerations were prioritized in decision-making. Decision-Making Process The decision-making process begins with the practitioner collecting contextual information, including existing transportation and land-use information as well as community priorities and policy objectives. Using this information, the framework user identifies the safety needs for each cross-section element and then evaluates whether the minimum safe roadway cross section fits within the available space. If the cross section does not fit within the available space, the frame- work prompts the user to identify changes that will allow the street cross section to be designed to provide the desired level of safety. The framework identifies what is needed to design a safe facility to enable the user to develop cross-section alternatives. The final step of the framework allows the user to compare alternatives according to performance measures selected at the out- set, thus allowing the user to weigh tradeoffs before selecting a preferred alternative. Choosing a Roadway Cross Section That Serves Your Vision Cross-Section Decision-Making and the Performance-Based Design Process The cross-section Decision-Making Framework reinforces the principles of performance-based design. Performance- based street design enables practitioners to make informed decisions regarding performance tradeoffs. FHWA’s Performance-Based Practical Design initiatives and NCHRP Report 785: Performance-Based Analysis of Geometric Design of Highways and Streets developed a framework for performance-based design.

2-2 Roadway Cross-Section Reallocation: A Guide The Decision-Making Framework (shown previously in Figure 1-2) consists of the following steps. Step 1: Define Your Limits and Set Your Goals In the framework’s first step, the user seeks to understand the purpose and bounds of a poten- tial street cross-section reallocation. Broader community information, such as community goals or city policies, will affect the value of cross-section tradeoffs. For example, a community with a Climate Action Plan might evaluate street-design decisions in terms of greenhouse gas emissions. Similarly, goals from local planning efforts should inform the comparison of the alternatives. The framework also prompts the user to designate whether a street’s primary function is “access” or “distributor.” Although significant changes to access are unlikely in the short term, streets designed for both access and mobility often have the most severe and highest number of crashes. The framework highlights this challenge and urges the user to make decisions that prioritize one of these two functions. (Chapter 5 discusses street functions and how they affect cross-section design in detail.) Additionally, given that the scope of a project is often limited in specific ways, the first step of the framework clarifies whether it is possible to move curbs or whether the project is limited to resurfacing and restriping. Finally, Step 1 is where the user will provide existing transportation and land-use data, includ- ing traffic volumes and speeds. (Chapter 3 describes the process for defining scope limitations while Chapter 4 presents information about community goals.) Step 2: Consider the Context Through a Safety Lens Based on the information resulting from Step 1, the framework suggests the minimum safe cross-section design. This cross section identifies a minimum safe design for pedestrians (e.g., sidewalk width and buffer; maximum distance between crossings), bicyclists (e.g., bicycle facility type, width, and buffer), drivers (e.g., lane width), and transit (e.g., lane width, if appropriate). The minimum safe facility for each mode depends primarily on traffic volumes and speeds, and secondarily on land-use context. (Chapter 7 presents information on the minimum dimensions for each cross-section element based on context.) In most cases, the framework identifies the need for pedestrian facilities, bicycle facilities, and travel lanes in each direction and/or on each side of the street. Streets with high traffic vol- umes or high traffic speeds require separated bicycle facilities and buffered sidewalks. (Chapter 5 describes how to design streets with safety as the top priority.) Step 3: Is There Enough Space to Build a Safe Road? Based on the results of Steps 1 and 2, the framework determines whether the minimum safe facility “fits.” In the case of a resurfacing project, the framework evaluates the space between the existing curbs. If the project has the potential for reconstruction, then the framework considers all available rights-of-way. (Chapter 7 identifies minimum safe dimensions for each cross-section element.) If the answer to Step 3 is “no,” then the framework goes to Step 4. If the answer to Step 3 is “yes,” then the framework skips Step 4 and goes to Step 5. Step 4: Overcome the Physical Barriers to Safe Road Design If the minimum safe dimensions resulting from Step 3 are not possible, the framework helps the user identify other options to achieve safety. Potential options include the following:

Choosing a Roadway Cross Section That Serves Your Vision 2-3   • Reducing vehicle speeds to permit narrower widths for travel lanes, bicycle lanes, and/or sidewalks; • Reducing vehicle volumes to reduce the width needed for bicycle lanes and/or sidewalks; • Identifying safe parallel facilities for bicycling that would reduce the needed width for bicycle lanes—“safe parallel facilities” must be deemed to comparably serve access and mobility needs for people biking; and • Converting a street with two-way traffic to one-way traffic to reduce the needed width for traffic lanes. Once a minimum safe facility is identified, the user continues to Step 5. (Chapter 6 provides information on how to overcome barriers to safe road design.) Step 5: Develop Design Options—What Happens When You Change Your Cross Section? In Step 5, the framework user can develop multiple cross-section alternatives. Drawing on the results of Step 1, the framework may prompt the user to consider certain cross-section elements. Possible cross-section items include the following: • Wider and more comfortable sidewalks; • Wider and more comfortable bike lanes; • Bus-only lanes; • Curbside uses (e.g., multimodal parking, streateries); • Medians; and • Additional general-purpose traffic lanes. Using the available space, the user would identify potential cross sections for evaluation. (Chapter 7 presents information on cross-section elements, including dimensions and effects on community goals.) Step 6: Evaluate and Choose the Cross Section That Serves Your Community’s Vision and Needs Finally, the framework supports users in evaluating cross-section tradeoffs through a com- parison of alternatives. The decision support matrix (Appendix B) presents information on the anticipated effects of cross-section changes on community goals. Practitioners can use this infor- mation to compare the alternatives they developed in Step 5. The primary goal for Step 6 is to address safety, traffic operations, and social, economic, and environmental needs. The Decision-Making Framework is also available as a spreadsheet tool, which is available by searching the National Academies Press website (nap.nationalacademies.org) for NCHRP Research Report 1036. The spreadsheet tool can help users as they work through the decision- making process and includes data and information presented in this Guide. The spreadsheet tool identifies a minimum safe cross section for a given street context and presents tradeoffs for various cross-section decisions. Appendix A provides a guide for using the tool. Appendix C presents the framework applied to a sample project. The Decision-Making Framework is presented as an infographic in Figure 2-1. This infographic illustrates the recommended process for planners, engineers, and the public to make decisions for cross-section reallocation. The infographic is a useful reference for practitioners and people in the community to work through tradeoffs in street cross-section designs and arrive at a pre- ferred vision. The infographic can be downloaded from the National Academies Press website (nap.nationalacademies.org).

Figure 2-1. Cross-Section Decision- Making Framework Infographic.