Roadway Cross-Section Reallocation: A Guide (2023)

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5-1   Safety for Everyone Recognizing that deaths and serious injuries from our transportation systems are both unac- ceptable and preventable, agencies increasingly are focusing on promoting safety. Ambitious policy goals at all levels of government call for a shift in mindset about street design that elevates safety above other priorities. Although most people can agree in the abstract that safety is most important, street designs that would improve safety are often met with resistance, especially if such designs could increase vehicle delay or reduce on-street parking. Tradeoffs between safety and other priorities are not easy to quantify, and concerns about effects on parking and delay are often voiced the loudest. Without clear guidance on what constitutes safe street design for all modes, practitioners are challenged to make safety the top priority. This Guide presents an approach to cross-section selection that begins with creating safe spaces for all street users. Building on contextual information, the framework identifies the necessary cross-section elements and their needed widths. By approaching the cross-section design and selection this way, the framework supports agencies’ goals of elevating safety. If decisionmakers want to prioritize other goals ahead of creating a safe street, they must at least acknowledge that decision explicitly and publicly. Making Street Functions Clear As described in Chapter 4, safe streets are designed with a clear function. Access streets, also known as local streets, primarily feature low speeds and a mix of transportation modes. Distribu- tor streets, also known as collector and arterial streets, serve a mobility function and should separate modes traveling at different speeds. Distributor streets should not have frequent access points to land uses because this situation creates the potential for conflicts between people turn- ing and people traveling through. Streets that mix aspects of these functions fail to produce a street “legible” to motorists and thus create dangerous conditions. These street categories are defined by their function and context. Ideal speeds and cross sec- tions vary with context, especially between the built-up area (i.e., urban and suburban environ- ments) and the non-built-up area (i.e., rural environments). For this Guide, we address safety approaches for cross-section allocations in urban and suburban environments. Highways with higher speeds (50 mph or greater) are not covered. The following sections provide information on the functions and typical characteristics of these street categories. Access Streets Also called local roads and neighborhood streets, access streets provide access to destina- tions (Figure 5-1). Local traffic (entering or leaving) is processed at all points along the street to serve the adjacent land uses (e.g., residential, commercial, or recreational). In urban contexts, C H A P T E R 5

5-2 Roadway Cross-Section Reallocation: A Guide pedestrians may use the street itself for a midblock crossing or to exit from a parked car. Vehicular speeds should be slow enough to allow these activities safely and comfortably. Typical characteristics are as follows: • Land-use context: Primarily residential, includes local services, destinations, and neighborhood- scale commercial uses; • Street elements: Unmarked lanes, narrow widths, minimal signs and markings, minimal mode separation, on-street parking, local deliveries, midblock curb cuts (residential and business), abundant access on road sections between intersections; • Typical ideal operating speed: 20 mph or lower (up to 25 mph possible but not recom- mended); and • Traffic characteristics: Low volume (<6,000 vehicles per day), primarily local traffic. Distributor Streets Also called collector or arterial streets, distributor streets link districts and regions (Figure 5-2). Distributor streets typically see higher vehicular speeds than access streets, provide direct con- nections to other parts of the network, and allow access primarily at intersections. Typical characteristics are as follows: • Land-use context: Mixed, with an emphasis on commercial and public services; includes local and regional services and destinations; • Street elements: Sharp definition between traffic and multimodal street elements, multiple lanes permitted, on-street parking discouraged, more signs and markings, mode separation, Figure 5-1. Access street. Figure 5-2. Distributor street.

Safety for Everyone 5-3   public transportation, local and regional deliveries, few driveway access points on road sec- tions between intersections; • Typical ideal operating speed: 20 to 35 mph; and • Traffic characteristics: Low-to-medium volume (6,000+ vehicles per day), primarily through traffic. The Problem with Gray Roads High-speed streets that serve both access and distributor functions are known as “gray roads” or “stroads.” They feature an incompatible mix of high traffic speeds and high volumes with driveways serving local destinations. Land uses along these roads generate multimodal trips with origins and destinations along both sides of the street. These roads often support transit services, creating many walking trips for people accessing the bus. But decisionmakers seek to minimize vehicle delay in support of the street’s distributor function, discouraging designers from adding multimodal infrastructure to serve these trips. Not fitting neatly into the access/distributor classification, these gray area roads perform poorly on various metrics, including the safety of all road users. Crash risks stem from high volumes of turning vehicles, with turns often executed mid- block, amid high vehicle speeds, and without adequate multimodal features and countermeasures. Similarly, street crossing opportunities for people walking and bicycling are often spread far apart and designed to minimize delays for drivers, resulting in uncomfortable and unsafe conditions. Benefits of a Network Plan and Clearly Articulated Street Function The importance of a clearly expressed street function goes beyond organizing prescribed features and facilities into categories. A clear purpose for every street can support a community’s vision for a place and deliver social and economic benefits beyond just mobility and safety. A street with a consistent and intuitive design is less stressful and more pleasant to experience, regardless of travel mode. A clear purpose also contextualizes a street’s functional role within its overall network (e.g., dis- tributor streets prioritize moving people through; access streets invite them to stay). By providing

5-4 Roadway Cross-Section Reallocation: A Guide a clear purpose for each street, a well-executed network plan can ease difficult decisions and sup- port more effective community engagement later in the corridor-level design process. A network with ambiguous street classifications and mismatched street designs and functions cannot be fixed all at once. By articulating the purpose of each street within the network, an essen- tial precursor to local street-level design decisions, a plan can offer the vision and logic essential to making local street-level design decisions that produce a comprehensive mobility network. Some states include land-use context—also known as context classification—in definitions of street function classifications. This approach enables the community to adjust design features to better reflect the multimodal needs of more densely developed areas. In urban and suburban land-use contexts, streets are fundamentally multimodal. A street’s function can inform whether the priority is moving people through the area or providing access to land uses. Managing Speeds for Safety Vehicle speed is the single most important factor in street safety. A Safe System approach (which puts rational, data-driven speed management at the core of every street-design project) is built on the idea that designers can implement a street designed to a target speed that matches its function and context. The Safe System Approach The idea of putting safety first goes by multiple names: “Safe System,” “Vision Zero,” and “Sustainable Safety.” Although there may be nuances among these approaches, this chapter focuses on their shared intent and values, using the term “Safe System approach,” which has been embraced by USDOT and other leading agencies, as a default. Example transportation safety initiatives recognizing that safety is the highest priority Targeted education and outreach campaigns and equitable law enforcement can help com- munities achieve lower speeds, but they should not be used to compensate for a failed design. In a Safe System approach, streets are designed to be self-enforcing. Strong coordination between policy, enforcement, and design is a precondition for effective speed management.

Safety for Everyone 5-5   Just as simply changing posted speed limits without accompanying engineering changes is unlikely to change the way a street works, design changes without strong policy, robust commu- nity engagement, and vision backing them are unlikely to result in systemwide implementation. Aligned leadership—elected officials and government staff—is essential to empowering designers to match speed to function. Absolute Risk Versus Exposure A core principle of a Safe System approach is that human mistakes in traffic are inevitable. Crashes resulting in death or severe injury, however, are preventable. Transportation systems must be forgiving in their design and execution. This premise invites a distinction between absolute risk and exposure risk. Put succinctly, speeds primarily influence absolute risk, while volumes influence exposure risk. Committing to a framework that elevates absolute risk can be a helpful strategy for gaining community support for a Safe System approach. Low numbers of active transportation users are often used to justify the lack of investment in safe facilities. If mitigating absolute risk is elevated as a top-priority safety goal, however, it may be easier to manage through-speeds. When safety is focused on absolute risk, high speeds are the biggest threat to people on the road. Volumes matter for facility design choices, but a Safe System approach puts absolute risk caused by the most dangerous modes at the forefront of risk assessment. How a Safe System Approach Puts Safety First Modern approaches to traffic safety consider broad societal factors, such as elected leadership and policy, social equity, and communications cultures, to craft a multilayered systemic strategy. Such approaches include targets and methods developed with diverse sectors of leadership (e.g., law enforcement, public health, and transportation). Practitioners rigorously and transparently use data to drive planning decisions at the network and corridor levels. A safety-first approach is multifaceted and requires strong leadership, robust and authentic public engagement, and collaboration across agencies, disciplines, and practices. For practitioners, a true safety-first approach also requires a shift in thinking about how streets are classified, designed, and operated. The five components of the Safe System approach (see Figure 5-3) are safe roads, safe speeds, safe road users, safe vehicles, and post-crash care. Safe streets and safe speeds are the direct focus of this chapter for two reasons: 1. Planning and engineering practitioners can directly enhance safety through street design and speed management. This chapter offers a conceptual framework for using functional Figure 5-3. The Five Elements of the Safe System Approach.

5-6 Roadway Cross-Section Reallocation: A Guide classification (safe streets) and speed management (safe speeds) as tools to establish a truly safety-first system in urban and suburban contexts. 2. Safe streets and safe speeds are the most impactful tools for proactively eliminating traffic deaths and serious injuries. Focusing primarily on these tools supports the secondary ele- ments of a Safe System, naturally leading to safer road users, mitigating the harm caused by vehicles, and limiting the need for and degree of post-crash care. A Safe System approach for everyone means aligning functions and design for contextu- ally appropriate speeds. Two fundamental principles of the Safe System approach should lead the design of every roadway: people are fallible and prone to making mistakes in traffic (some crashes are inevitable), and vehicle speeds above 20 mph are exponentially more likely to result in serious injury or death in a collision. (Readers are encouraged to consult Chapter 6 for detailed strategies for designing for safety.) Multimodal features and countermeasures vary with context. But if a mismatch between street function and design results in a dangerous street, a safety-first approach requires practitioners to revisit the design—and its performance—until it meets safety targets. A system that truly prioritizes safety requires a bold rethinking of established practices and habits. Change is difficult. Although an uncompromising commitment to a Safe System approach is the absolute goal, smaller, incre- mental changes may be necessary if the political and public will are not sufficient to make the necessary changes to street space allocations all at once. Being proactive and systematic about safety is a basic expectation. Whether a street is being repaved or fully reconstructed, a proactive approach to addressing risk factors and mitigating the harm caused by potential crashes should be part of the design process. This approach puts safety first by using data to anticipate risks and build for a safer situation, rather than responding to crashes with retroactive countermeasures. Applying a Safe System Approach Developing a Safe System approach for a street should consider the category of the street (e.g., access or distributor). The sections below explore these categories further and present information on topics such as speed management, volume, vehicle mass, shared streets, and curbside uses. Access Streets Local access streets constitute most roads in U.S. cities and towns. Although varying widely in shape and style, and with posted speed limits commonly between 20 and 35 mph, local access streets present a significant opportunity to maximize safety and provide consistency throughout a network. Access streets should not be designed for speeds above 20 mph. The primary purposes of access streets are connecting people to end destinations, strengthening the quality of place, and providing for the safety and comfort of residents (Figure 5-4). A growing number of U.S. municipalities are adopting default speed limits of 20 mph for local streets in urban areas, a target speed consistent with best practices from around the world. In most neighborhoods, planners and designers will find strong community support for mini- mizing the safety and health effects of high-speed vehicle traffic. When the vehicle speeds and volumes are low, access streets perform well as low-stress links for cycling and walking networks with minimal additional infrastructure investments. In addition to the mobility functions, access streets can act as valued amenities to residents, providing safe public space for recreation and socializing.

Safety for Everyone 5-7   Speed Management Internationally, the consensus among practitioners is that a maximum speed of 20 mph/30 km/h provides an optimum balance of safety and efficiency on mixed-use local streets. The likelihood that a pedestrian or bicyclist will survive a collision with a moving car drops dramatically as vehicle speeds exceed 20 mph (see Figure 5-5). In most contexts, the effects of slower speeds on travel times are negligible, because people drive on access streets for short distances and most delay is attributed to Stop signs and signals. The 20-mph speed limit provides a secondary benefit of inviting and integrating more active transportation users, which increases safety through the safety-in-numbers effect. In most con- texts, limiting vehicle speeds on access streets to 20 mph allows modes to mix safely and comfort- ably without specific infrastructure accommodations. Volume Based on a maximum operating speed of 20 mph, most access streets serve mixed traffic safely and comfortably. As volumes approach 2,000 vehicles per day and beyond, however, an access Figure 5-4. Example access street designed for slow speeds in Minneapolis, MN. THE LIKELIHOOD OF FATALITY INCREASES EXPONENTIALLY WITH VEHICLE SPEED32 100% 75% 50%Likelihood of Death 25% 0% Hit at 23 mph, 10% of people will die Hit at 32 mph, 25% of people will die Common Speed Limits on Urban Arterials Hit at 50 mph, 75% of people will die Impact Speed 15 MPH 25 MPH 35 MPH 45 MPH 55 MPH Figure 5-5. The Influence of Impact Speed on the Probability of Death (Credit NACTO (2020)).

5-8 Roadway Cross-Section Reallocation: A Guide street’s performance as a link in the pedestrian and cycling network and a community public space may decline. Quality of place may also suffer. This may have the adverse effect of decreasing the number of bicyclists and minimizing the perception of safety, so, even if low speeds make for an objectively safe street, the network may decline. On streets with traffic volumes greater than 2,000 vehicles per day, additional engineering measures such as traffic-calming, painted bike lanes, or marked crossings may be necessary to maintain a high level of comfort and usability. Contextually appropriate traffic-calming mea- sures may be necessary to ensure actual operating speeds of 20 mph or lower. Access streets with traffic volumes exceeding 6,000 vehicles per day are no longer truly access streets and should trigger an evaluation to determine whether there is a mismatch between the planning function and the performance of the road and whether reclassification is required. Vehicle Mass The types of vehicles and their relative masses also factor into the design of access streets. Where an access street serves a role in freight or public transportation networks, additional steps are likely needed to ensure safe conditions for all users. More commonly, schools are often located on access streets, necessitating design considerations for school buses. In principle, the greater the difference in mass between users, the greater the need for separa- tion, even when operating speeds are effectively capped at 20 mph. A narrow roadway is critical to managing speeds and ensuring that all modes mix safely and comfortably. When engineering and policy unite to create conditions for low (≤20 mph) travel speeds, travel modes can mix and share space safely and harmoniously. However, in practice, these ideal conditions are not always present. In situations where large vehicles such as trucks or buses are expected, or when average daily traf- fic is higher than desired on an access street, integrating enhanced physical or temporal separation between modes can help to direct desired behavior and improve comfort and usability. Contextually appropriate bicycle and pedestrian infrastructure or traffic-calming elements can be implemented. Shared Streets Sidewalks and crossing treatments provide safe and comfortable pedestrian functionality on most access streets. The primary variations in pedestrian space are determined by the balance of modal volumes, land use, and planning goals for a street. Generally, pedestrian space is separated by grade (e.g., the difference between a traditional sidewalk and a shared street, in which the pedestrian space is level with the roadway). Various crossing treatments that incorporate grade, markings, and signs complete the pedestrian realm. In some access street types, particularly those with heavy commercial use and very high pedes- trian volumes, a completely shared street without defined pedestrian facilities can perform well (Figure 5-6). These streets can produce some of the most vibrant and economically successful environments in their communities. Regardless of the elevation and markings, space should be reserved on the street edges for users with limited mobility. FHWA’s Accessible Shared Streets: Notable Practices and Consider- ations for Accommodating Pedestrians with Vision Disabilities provides guidance on designing shared streets for accessibility (Elliott et al. 2017). Advisory bike lanes (also known as advisory shoulders or edge-lane roads) can improve delin- eation for people bicycling on shared streets. Distributor Streets Distributor streets are essential to the multimodal street networks in urban and suburban areas. Distributor streets provide for local and regional access while connecting to and often

Safety for Everyone 5-9   containing, commercial and civic destinations. Distributor streets facilitate the movement of personal cars, public transportation, delivery and commercial vehicles, emergency response vehicles, school buses, pedestrians and bicyclists, and people using mobility devices such as e-scooters and wheelchairs. With multiple modes operating at different speeds and with dif- ferent goals, distributor streets require nuanced design and operation to be safe and efficient (Figure 5-7). Distributor streets connect people to local access streets and their destinations, as well as to arterials, regional limited-access streets, and highways. Distributor streets are often key public transport corridors. Direct access from adjacent properties can be permitted where it does not introduce traffic safety or capacity concerns. Compared to local roads, carefully considered access and more robust speed management are keys to ensuring a safe environment on distributor streets. Traffic flows along the corridor, while access occurs at intersections. Prioritizing both traffic flow and access to destinations on distributor streets is unlikely to work because these are largely incompatible goals. Optimal policy and design, informed by land-use planning and network goals, will identify one goal or the other as the priority. Speed Management Speeds on distributor streets can be influenced by various cross-section design decisions (e.g., travel lane widths, the number and type of lanes, and the use of vertical elements such as median islands). These design choices narrow the roadway both dimensionally and visually. Typically, Source: www.pedbikeimages.org / Dan Burden Figure 5-6. A shared street in Madison, WI. Figure 5-7. A shared-use path along a distributor street in Minneapolis, MN.

5-10 Roadway Cross-Section Reallocation: A Guide the narrower the lanes and the more visually restricted the space, the easier it is to mitigate the dangers posed by fast-moving vehicles. In a Safe System approach, the ideal operating speed for distributor streets in urban and sub- urban areas is 30 mph. In practice, distributor streets can be safely engineered for ranges from 20 mph to 35 mph, with greater separation between modes needed to maintain safety as design speeds increase. Distributor streets with operating speeds from 35 mph to 50 mph are common in U.S. cities and towns, despite the significant safety challenges these speeds pose. When operating speeds exceed 20 mph, varying degrees of physical mode separation need to be considered, with the intensity of separation generally increasing with speed (Figure 5-8). The engineering techniques for implementing modal separation are vast, varied, and dependent on local context and goals. However, it is helpful to consider physical separation measures as a spectrum, with light separation (e.g., painted bike lanes and pedestrian crosswalks) at one end and heavy separation (e.g., rigid barriers and separated phases at signalized intersections) at the other. Streets with operating speeds at or above 50 mph are not considered distributor streets. Such speeds should be reserved for limited-access highways. Active transportation can be safely inte- grated parallel to such roads, with the creation of a completely separated adjacent route (e.g., a multiuse path) that includes robust spatial and temporal insulation between modes; however, such a choice can be expensive. The ideal type of bicycle infrastructure for distributor streets varies with the speed, volume, and mass of motorized traffic. For speeds and volumes up to 25 mph and 6,000 vehicles per day, a painted, or painted and buffered, bike lane is typically sufficient for safe and comfortable bicycling. Between 25 and 35 mph, light physical separation is the minimum safe requirement. Alternatively, a vertically separated (e.g., raised) bicycle lane is acceptable for providing light separation. On routes with more than 6,000 vehicles per day or high volumes of heavy vehicles (e.g., frequent-service bus routes or freight routes), an upgrade to heavier separation is advised, even if speeds remain at or below 25 mph. Other factors affecting the choice of bicycle facilities include the presence and frequency of on-street parking, midblock driveways, transit stops, and loading zones. Speed management and degrees of physical separation are intrinsically linked. Safety can be provided by lower speeds, physical separation, or both. The task of the designer is to match the degree of separation to the conditions of the distributor street, with higher speeds demanding heavier separation and lower speeds requiring lighter measures. Figure 5-8. A separated bike lane along a distributor street in Cambridge, MA.

Safety for Everyone 5-11   Volume Vehicle volumes on distributor streets can help determine what level of separation between modes is needed and how to best design intersections. With maximum operating speeds of 25 mph and fewer than 6,000 vehicles per day, painted markings or signs alone typically can provide sufficient separation and safe intersections. Above 6,000 vehicles per day, safe facilities include vertically separated bike lanes or protected bike lanes with physical barriers such as posts, curbs, or planters. The ideal minimum width of the bicycle facility also increases from 5.5 to 6 feet to increase both the room for error and the overall level of comfort and to allow bicyclists to pass one another safely. On higher-volume and higher-speed distributor streets, where operational speeds exceed 30 mph or where daily vehicle volumes exceed 6,000, heavier separation (e.g., curbs, rigid bol- lards, and concrete planters) is necessary. A vertically separated bike lane is sufficient, given a 2-foot buffer. These facilities are not limited to bicycles—many forms of micromobility with oper- ating speeds of 15 to 20 mph (such as e-scooters) can comfortably and safely use such facilities. Curbside Use In general, curbside uses other than public transportation stops on distributor roads should be minimized. Where on-street parking and other curbside activities are functional or political requirements, the designer should consider whether the functional classification of the road is appropriate. Why is parking needed? Are there shops and businesses that people cannot access with any other parking solution? If so, perhaps the road ideally functions within its network as an access street. If this is the case, design for slower speeds and more accommodation for starting, stopping, and midblock intersections. Local traffic should be considered. In practice, many distributor streets serve a dual function as both distributor and access by providing on-street parking. Curbside parking serves as a de facto buffer between sidewalks and travel lanes and can be offset from the curb to provide parking-separated bicycle facilities. High-turnover on-street parking can also be an asset for speed management, creating friction that helps encourage safe speeds. Smart use of curbside space is an important tool for aligning transportation and land-use goals (see Figure 5-9). Curbside uses that may be practical on distributor streets include the following: • Public transportation stops, • Loading/unloading zones, • Micromobility docking stations and on-street bike and e-scooter parking corrals, What About Painted Bike Lanes? For years, painted bike lanes on a distributor street with operating speeds of 30 mph and higher were considered a best practice (and the only solution available) in the United States. Over the past decade, the practice has moved beyond the basic bike lane as a one-size-fits-all solution for every non-access street. In a Safe System approach, the level of separation provided by a painted bike lane is not sufficient to mitigate the worst effects of crashes involving cars and bikes, nor is it comfortable and intuitive enough to invite less experienced cyclists to use it. Either speeds must be managed at lower levels or more robust separation must be introduced, including at intersections. Guidance for selecting the appropriate bicycle facility based on context is presented in Chapter 7.

5-12 Roadway Cross-Section Reallocation: A Guide • On-street car parking, and • Landscaped medians. Curbs can also be extended to reduce pedestrian crossing distance, minimize conflict zones, and tighten turn radii. Although vehicle access on distributor streets ideally occurs at intersections, distributor streets that require curbside space are also likely to have driveways and other mid- block turning movements. Driveways and driveway widths should be reduced where possible to minimize conflict areas between vehicles and active modes. Distributor streets are used in many ways in U.S. communities. Harmonious integration between land use and transportation is especially important on these midsized connectors. Speed and Street Type Matter Safety is a multidisciplinary, systemic issue that requires action on multiple fronts. For the transportation professional, street design is the most powerful tool for achieving safety. Clear, intuitive alignment of street function and design through classification and speed management are fundamental pillars of a Safe System approach. Every street’s purpose should be clearly articulated by policy and supported by self-enforcing design. Most access streets in our communities already support mixing multimodal traffic at speeds lower than 20 mph and carry low volumes of vehicles. Although robust separated infra- structure with special attention at intersections can enable safe and comfortable travel on distributor streets and other roads where faster speeds and higher volumes are needed, further investment is needed to accomplish this. What happens when a Safe System approach is not feasible for a given project? Chapter 6 addresses such scenarios. When comprehensive transformation of a street network is not possible immediately, some approaches improve cross-section safety for short-term needs while moving toward a truly Safe System in the long term. Summary Commit to a clear and simple function for each road in the network. Do not ask all streets to do everything for everyone. Speed management and road design are primary elements of a Safe System approach. Be systemic, data-driven, and proactive about safety. Source: www.pedbikeimages.org / Nathan Roseberry Figure 5-9. The curb along a distributor street is used for a floating bus stop in Chicago, IL.