CHAPTER 16
Complete Streets

Complete Streets Overview and Heuristics

Complete Streets and Similar Initiatives

A Framework for Selecting Complete Streets Implementations

A Framework for Complete Streets Evaluations

Key References for Complete Streets Design Information

COMPLETE STREETS OVERVIEW AND HEURISTICS

Introduction

The core human factors concept of Complete Streets is to provide individuals with the ability to use both/either driving and non-driving modes to travel easily, efficiently, and safely. Complete Streets has several definitions (1), but key themes are shared across Complete Streets resources. The goal of Complete Streets is to develop an unbroken surface transportation network for multimodal connectivity (2) and consistently design and construct the right-of-way to accommodate all anticipated users (3). Not all modes need to be accommodated on all roads (1), but specific roads can be designated to emphasize different modes based on road type and community context (3) to achieve an unbroken network (1). The Complete Streets approach requires bicyclist and pedestrian accommodation within the network (2). Other modes may also be accommodated, including public transportation users, motorists, freight vehicles, emergency response vehicles, and equestrians (2, 3). Complete Streets policies and projects aim to provide safe use of roadway facilities for all users of the network, regardless of modality, age, and ability (1, 2, 3, 4). In 2018, this framework was updated to provide for a greater emphasis on equity and providing service in underinvested communities (e.g., improving access for individuals with disabilities) (5).

Complete Streets objectives apply not only to planning new projects but also to new and retrofit projects at the planning, design, maintenance (including resurfacing, repaving, restriping, and rehabilitation), and operation stages (3, 6, 7, 8). Complete Streets include the continuation of multimodal support during construction, repair work, special events, and inclement weather, for example, maintaining snow storage space that does not obstruct any one mode of transportation (1).

In contrast to traditional infrastructure planning and design practices, Complete Streets aims to balance how transportation needs of motorized and non-motorized users are weighted by lowering the priority of automobile-focused metrics, e.g., improving the level of service or reducing average daily traffic (ADT) (4, 8) and introducing and prioritizing metrics that reflect the safety, access, and mobility of multiple modes (1, 4).

Design Guidelines

Complete Streets evaluations are commonly performed for both policy and implementation (5). The Complete Streets framework contains ten elements. Policies are evaluated against criteria that map to each element and are scored out of 100. The policy evaluation criteria were last updated in 2018 (3, 5, 6). Long Description. The table has 3 columns: Column 1: Complete Streets Element. Column 2: Description. Column 3: Score Row 1, Column 1: Establishes commitment and vision. Column 2: Specifies a vision for why and how the community wants to complete its streets. Includes pedestrians, bicyclists, transit passengers of all ages and abilities, as well as trucks, buses, and automobiles. Column 3: 12 Row 2, Column 1: Prioritizes underinvested and underserved communities. Column 2: Defines priority groups (the communities or areas that have been underinvested and underserved) and prioritizes those communities. Column 3: 9 Row 3, Column 1: Applies to all projects and phases. Column 2: Applies to new projects and retrofit projects (including design, planning, maintenance, and operations) for the entire right-of-way. Column 3: 10 Row 4, Column 1: Allows only clear exceptions. Column 2: Makes any exceptions specific and sets a clear procedure that requires high-level approval. Column 3: 8 Row 5, Column 1: Mandates coordination. Column 2: Requires compliance and coordination between private developers, government departments, and partner agencies. Column 3: 8 Row 6, Column 1: Adopts excellent design guidance. Column 2: Recognizes the need to be flexible to meet user needs while using the latest and best design criteria and guidelines. Column 3: 7 Row 7, Column 1: Requires proactive land-use planning. Column 2: Solutions complement the context of the community, as well as the current and expected land-use and transportation needs. Column 3: 10 Row 8, Column 1: Measures progress. Column 2: Defines performance standards with measurable outcomes. Column 3: 13 Row 9, Column 1: Sets criteria for choosing projects. Column 2: Establishes specific criteria to encourage project selection for Complete Streets implementations or projects that address equity issues. Column 3: 8 Row 10, Column 1: Creates a plan for implementation. Column 2: Outlines who, when, and how policy implementation will occur using actionable and specific steps. Column 3: 15 Row 11, Column 1: Total Column 2: blank. Column 3: 100

Long Description. A scale from 0 to 6 where 0 represents ‘Based Primarily on Expert Judgment,’ 6 represents ‘Based Primarily on Empirical Data,’ and 3 represents ‘Based Equally on Expert Judgment and Empirical Data.’ This guideline ranks a 2 on the scale.

Discussion

Benefits. Complete Streets projects are associated with increased property values and job growth (9) along the project corridors. Complete Streets projects can also increase bicycle and foot traffic, improve corridor safety, and improve bus travel times (see 10). In addition, multimodal connectivity provides individuals who are unable to drive with more transportation options and drivers with the option to use other modes of transportation (7).

Recommended approaches. Agency policies, procedures, and design guidelines should be written or adapted to serve all modes (8). Coalition building of government stakeholders and advocacy groups is a key step to policy implementation. Without regional and local buy-in, Complete Streets policy adoption may not translate into implemented projects (11). Running pilot programs may foster buy-in (11), and base data should be collected on all users and modes for meaningful before-and-after performance measures (8). Formalized policy adoption is useful as a tool to continue momentum, reinforce incremental change, and solidify progress (11). Policy adoption may also help facilitate training initiatives (12). Training or hiring staff skilled in multimodal accommodation is also recommended to improve the effectiveness of a Complete Streets initiative (8).

Performance metrics. Within the Complete Streets framework, the “Measures Progress” section of a Complete Streets policy outlines the metrics or types of metrics that practitioners will use to assess the implementation of a given project (5). The Complete Streets approach is not prescriptive about the exact metrics used and allows communities to define and use their own evaluation metrics (3, 8). These metrics are generally concerned with multiple transportation modes (e.g., walking, biking, driving) and are often supported by metadata to track certain types of performance. For tracking performance related to Complete Streetsʼ equity criteria, measurable definitions of priority groups may be needed, along with measurable definitions of the geographical area belonging to each facility or road segment of interest. Thus, recommended policies from guidance documents include plans for data collection workup, timelines for recurring performance metrics collection and publishing data and analyses, and assigning staff to manage data collection, storage, cleaning, analyses, and reporting (2, 5, 6).

Design Considerations

Safety assessment of proposed designs. When using HSM (Highway Safety Manual) predictive models to assess the safety of Complete Streets designs, most of the existing models for urban roadways focus on arterial roads rather than local and collector roads [e.g., the model described in Barua et al. (13)]. Groups can develop their own models for different roadway types, but this process requires substantial effort (see 14 for a process example). Designers may use crash modification factors (CMFs) to help account for the differences between proposed designs and the HSM base models, but it may still be difficult to find appropriate CMFs (e.g., for different types of on-street parking locations) or to prioritize which CMFs to include (the HSM recommends including a maximum of three CMFs; 13).

Data collection and data storage challenges. Collecting before-and-after metrics (8) can be difficult, especially those that can indicate injuries and fatalities related to pedestrian and bicyclist exposure (15). Implementing the digital infrastructure to store and access data may also require substantial effort. California Department of Transportation (Caltrans; 16) set an objective to implement a comprehensive Pedestrian Safety Data Plan in 2009, which included gathering pedestrian exposure data. Developing a statewide active transportation count database continues to be an ongoing effort more than 10 years later (17).

Cross References

None.

Key References

COMPLETE STREETS AND SIMILAR INITIATIVES

Introduction

This guideline discusses the main themes of Complete Streets, the relationship between Complete Streets, Context Sensitive Solutions (CSS), and the Safe System Approach. It also reviews Complete Streets evaluation metrics related to human safety and performance and provides some real-world case studies of Complete Streets evaluations. In general, Complete Streets emphasizes network design and provides a framework for policy development and adoption to facilitate a coordinated network design effort rather than a fragmented project-by-project approach (1, 2). On the other hand, CSS aims to allocate funds, time, and a concerted effort to involve stakeholder groups from the beginning of the project, including those who do not live in the project area but would be impacted by it (3).

Differences between CSS and Complete Streets. CSS focuses on ensuring that a project fits into its external context (e.g., environmental, social) (3, 4). In contrast, Complete Streets focuses on the roadwayʼs internal context (e.g., the road users) and making multimodal accommodation routine (4). In CSS, practitioners work to understand who the core users of a project (including community and business groups) are and what their needs are (5), whereas the Complete Streets approach focuses on formally designating intended road users even if they are not currently served in an area (e.g., bicyclists and pedestrians). CSS does not mandate data collection and evaluation based on predetermined performance measures.

Design Guidelines

Long Description. The table has 3 column: Column 1: Initiative. Column 2: Goal. Column 3: Approach Row 1, Column 1: Complete Streets. Column 2: Facilitate a coordinated multimodal transportation network, see Key References 1, 2, 6. Column 3: Policy development and adoption (1, 2). Ten elements framework, see Key References 1, and 6. Establishes commitment and vision. Prioritizes underinvested and underserved communities. Applies to all projects and phases. Allows only clear exceptions. Mandates coordination. Adopts excellent design guidance. Requires proactive land-use planning. Measures progress. Sets criteria for choosing projects. Creates a plan for implementation. Row 2, Column 1: Context Sensitive Solutions. Column 2: Ensure that a project fits into its external context (i.e., environmental, social) and meets the needs of its users, see Key References 3, 4, and 7. Column 3: Allocate funds, time, and a concerted effort to involve stakeholders, see Key References 3 and 7. Involve stakeholders from the beginning of the project, see Key References 3, 4, and 7. Stakeholder groups include those who will be directly and indirectly impacted by the project, see Key References 3 and 7. Row 3, Column 1: The Safe System Approach. Create a road environment that maximizes safety performance (Key References 8, 9, 10, 11). Column 2: Anticipate and accommodate human limitations and errors, see Key References 8, 9, and 10). Reduce kinetic energy transfer see Key References 8, 9, and 10. Six principles, see References 8 and 11. Death/serious injury is unacceptable. Humans make mistakes. Humans are vulnerable. Responsibility is shared. Safety is proactive. Redundancy is crucial. Five elements, see Key References 8 and 11: Safe road users. Safe vehicles. Safe speeds. Safe roads. Post-crash care.

Long Description. A scale from 0 to 6 where 0 represents ‘Based Primarily on Expert Judgment,’ 6 represents ‘Based Primarily on Empirical Data,’ and 3 represents ‘Based Equally on Expert Judgment and Empirical Data.’ This guideline ranks a 3 on the scale.

Discussion

Leveraging a CSS approach within Complete Streets. Integrating stakeholders early in any project facilitates a feeling of project ownership, which can help prevent community members from contesting a design in ways that could result in the delay or cancellation of a project (3, 4, 7). Local contexts and different settings (i.e., urban, suburban, and rural) are highly relevant to Complete Streets since they change the needs of road users and affect whether it makes sense for a road to accommodate a specific mode or when exceptions may be warranted [e.g., for severe topological constraints (12)].

The Safe System Approach (which includes the Vision Zero, Toward Zero Deaths, Road to Zero Coalition programs) seeks to create a road environment that maximizes safety performance for all road users by not accepting that death and serious injury are a natural consequence of using a road system (8, 9, 10, 11). Rather than relying primarily on improving human behavior, the Safe System Approach aims to anticipate and accommodate human limitations and errors. Safe System Approaches plan, design, and operate a road system that recognizes humans make mistakes, have limited physiological abilities to safely negotiate complex situations, and have a limited tolerance of kinetic energy forces. Therefore, a goal of this approach is to create a system that reduces the risk of kinetic energy transfer occurring in the first place and reduces the amount of energy transfer in the event of a crash to an amount that can be tolerated by humans (8, 9, 10, 11).

Differences between Safe System and Complete Streets. Safe System includes six core principles and five elements (8, 11). These principles and elements go beyond Complete Streetsʼ focus on road users, roadway facilities, and network design to include vehicle design and post-crash care. These additional considerations entail stakeholder involvement from the larger transportation ecosystem (e.g., OEMs, emergency first responders, law enforcement) to implement in-vehicle safety systems [e.g., seat belt interlocks, alcohol interlocks, intelligent speed limiters; (9)] and improve data collection from crash sites (8).

While Complete Streets designs often include facilities that, to facilitate multimodal use and safety, also work as traffic speed control measures (4), the Safe System Approach focuses on examining speed proactively to reduce the occurrence of lethal energy transfer, and may use travel speeds and typical road user mass to determine when and how road users will be separated in time (e.g., using traffic signals) or in physical space (e.g., using grade separation or physical barriers, or intersection designs that reduce conflict points) (8, 9, 10). For example, this could generally mean separating high-speed roads from mixed land use spaces (10). Scurry and Hopwood proposed a four-tier Safe System Hierarchy to prioritize countermeasure selection: remove severe conflicts, reduce vehicle speeds, manage conflicts in time, and increase attentiveness and awareness (13) based on the Hierarchy of Controls for Traffic Safety framework (8).

Leveraging Safe System within a Complete Streets approach. Leveraging Safe System can help improve safety in multimodal corridors, especially where space constraints and speed differentials between modes may result in poor crash outcomes (8).

Design Considerations

Similar to Complete Streets, Safe System roadway functional class and modal priorities can help support safe roads by identifying safety countermeasures that are most effective for a given type of facility (8). For example, it is not recommended to formally designate and promote a bike route along arterial road classes that, as assessed, cannot accommodate an appropriate facility type (14).

Key References

A FRAMEWORK FOR SELECTING COMPLETE STREETS IMPLEMENTATIONS

Introduction

The Safe System Design Hierarchy from FHWA (1) characterizes how well engineering and infrastructure-based countermeasures align with different methods for achieving zero traffic deaths and severe injuries through reducing the risk of kinetic energy transfer. This tool is based on the hierarchy of controls for workplace safety and previous work by Austroads (1). Complete Streets can use many different roadway implementations to achieve the goal of an unbroken multimodal network. By applying the Safe System Design Hierarchy to Complete Streets initiatives, designers can identify and prioritize network implementations that are associated with desired safety outcomes (1).

Design Guidelines

The Safe System Design Hierarchy framework uses a four-tier hierarchy: (1) remove severe conflicts, (2) reduce vehicle speeds, (3) manage conflicts in time, and (4) increase attentiveness and awareness. The tiers reflect human factors issues that are key to the efficacy of roadways as communication devices and general safety performance (i.e., crash frequency and severity) of roadways: perception-response time, expectations, visibility, and workload (2). The following table [source: (1)] maps proven countermeasures to each tier. See more about proven countermeasures at https://highways.dot.gov/safety/proven-safety-countermeasures. Long Description. The following countermeasures are in the Intersections cateogry: Backplates with reflective borders: Tier 4.: Corridor Access Management: Tier 1.: Dedicated left and right turn lanes at intersections: Tier 1. Reduced left turn conflict intersections: Tier 1.: Reduced left turn conflict intersections: Tier 1.: Roundabouts: Tier 1 and 2.: . Systemic application of multiple low-cost countermeasures at stop-controlled intersections: Yellow change intervals: Tier 3. The following countermeasures are in the Speed Management category:. Appropriate speed limits for all road users: Tier 2. Speed safety cameras: Tier 2. Variable speed limits: Tier 2. The following countermeasures are in the Pedestrian/Bicyclist category: Bicycle lanes: Tier 1 . Crosswalk visibility enhancements: Tier 4. Leading pedestrian interval: Tier 3. Medians and pedestrian refuge islands: Tier 1 and 2. Pedestrian hybrid beacons: Tier 3. Rectangular rapid flashing beacons, RRFB: Tier 4. Road diets: Tier 1 and 2. Walkways: Tier 1. The following countermeasures are in the Roadway Departure category: Enhanced delineation for horizontal curves: Tier 4. Longitudinal rumble strips and stripes: Tier 4. Median barriers: Tier 1. Roadside design improvements at curve: Tier 1. Safety Edge SM: Tier 1. Wider edge lines: Tier 4. The following countermeasures are in the Crosscutting category:. Lighting: Tier 4. Local road safety plans: Tier 1, 2, and 3. Pavement friction management: Tier 1 and 2. Road Safety Audit: Tier 1, 2, 3, and 4.

Long Description. A scale from 0 to 6 where 0 represents ‘Based Primarily on Expert Judgment,’ 6 represents ‘Based Primarily on Empirical Data,’ and 3 represents ‘Based Equally on Expert Judgment and Empirical Data.’ This guideline ranks a 3 on the scale.

Discussion

Safe Systems Design Hierarchy. This four-tier framework helps practitioners arrange safety countermeasures and strategies from most to least aligned with the Safe System principles, where physical changes to the system are considered more effective than relying solely on road users to make safe decisions (1).

Tier 1: Remove severe conflicts. Removing high-risk conditions reduces severe conflicts. Complete Streets often minimize conflicts by separating travel modes and directions of travel in space based on differences in weight, speed, and expected traffic volumes (3, 4) or selecting designs with fewer conflict points. A road diet converts an undivided four-lane roadway into a three-lane divided roadway consisting of two through lanes and a center two-way left-turn lane. This allows for the reallocation of space for other modes or functions (e.g., bike lanes, pedestrian refuge islands, transit uses, parking). Road diets improve safety by reducing the number of vehicle-vehicle and vehicle-other road user conflict points and reducing speed differentials: through-lane lead vehicles limit speed differentials, and through-lane vehicles are separated from left-turning vehicles (5).

Tier 2: Reduce vehicle speeds. In the event of a crash, reducing vehicle speeds reduces the kinetic energy transfer. Complete Streets designs often include speed management (3, 4). For example, self-enforcing roadways (see 6) use a target design speed to select a roadwayʼs vertical and horizontal alignment and other geometric properties and then support road usersʼ selection of this speed with traffic signs, pavement markings, and other roadside elements (6). Protected intersections may use corner safety islands with a small turn radius, which necessitate slower motorist turning speeds. Reducing the turning radii not only manages vehicle speed but also orients the vehicle in a way that improves the visibility of pedestrians and bicyclists to drivers (7).

Tier 3: Manage conflicts in time. When road users need to occupy the same physical space, conflicts may be managed by separating road users in time using traffic control devices. A leading pedestrian signal allows pedestrians to cross lanes of travel prior to vehicle movement and can increase a turning driverʼs awareness of crossing pedestrians (8).

Tier 4: Increase attentiveness and awareness. Alerting road users to potential hazards or conflicts supports appropriate reactions. For example, curb extensions, which extend the sidewalk or curb line into the parking lane, can reduce the crossing distance of pedestrians (reducing exposure) while improving the sight distance and sight lines of both pedestrians and motorists (8).

Design Considerations

Multimodal considerations. Safety countermeasures and strategies have implications for how different modes interact in space. Designs may benefit multiple modes (e.g., loading zones can benefit ride shares as well as freight). There are also common “foibles” of multimodal interactions, but these may be circumvented through geometric design. For example, bicyclists performing passing maneuvers may interfere with buses at bus stops (9). Drivers are more likely to focus their attention on hazards in the forward view and may have difficulty perceiving bicyclists approaching from behind (4), both while driving and stationary (e.g., while opening their door) (9). Rumble strips can interfere with bicycles, but some designs are bicycle-tolerable (10). In a Complete Street, driver expectations and culture may also need to shift from arriving at their destination in the most expedient manner to prioritizing courteous driving, planning for adequate travel time, and resisting pressure from other traffic to speed (11).

Cross References

A Framework for Complete Streets Evaluations

Key References

A FRAMEWORK FOR COMPLETE STREETS EVALUATIONS

Introduction

While Complete Streets evaluations are defined at the policy creation stage, implementation assessment metrics, although encouraged, are not prescriptive. Within the Safe Systems Approach framework, however, there has been more development of specific guidance for selecting and assessing implementation strategies. The Safe System Assessment Framework by Austroads aims to help road agencies methodically consider Safe System objectives in road infrastructure projects (1). It uses the five elements of the Safe System Approach to assess how well a given project aligns with key principles (1).

Design Guidelines

Practitioners can evaluate a Complete Streets project against the Safe System Matrix illustrated in the table below [source: (1)] to ensure that all five Safe System elements are considered (i.e., safe road users, safe vehicles, safe speeds, safe roads, post-crash care) and measure how well a project aligns with the six Safe System principles (i.e., death/serious injury is unacceptable, humans make mistakes, humans are vulnerable, responsibility is shared, safety is proactive, and redundancy is crucial) (1, 2, 3). Long Description. The table has 7 columns, each listing crash types: Column 1: Crash Type; Run-off-road. Column 2: Head-on. Column 3: Intersection. Column 4: Other. Column 5: Pedestrian. Column 6: Cyclist. Column 7: Motorcyclist. The table has 3 rows listing risk assessment factors: Row 1, Exposure. Row 2, Likelihood. Row 3: Severity. The data for each row are as follows: Exposure; AADT (annual average daily traffic), length of road segment; AADT, length of road segment; AADT for each approach, intersection size; AADT, length of road segment; AADT, pedestrian numbers, crossing width, length of road segment; AADT; cyclist numbers, pedestrians; AADT, motorcycle numbers, length of road segment. Row 2: Speed; geometry; shoulders; barriers; hazard offset; guidance and delineation; Geometry; separation; guidance and delineation; speed; Type of control; speed; design, visibility; conflict points; sight distance, number of lanes, surface friction; Design of facilities, separation, number of conflicting directions, speed; Design of facilities, separation, speed; Design of facilities, separation, speed. Row 3: Severity; Speed, roadside features and design (e.g., flexible barriers); Speed; Impact angles, speed; Speed; Speed; Speed; Speed Long Description. General guiding assessment questions for the Road user element include the following: Are road users likely to be alert and compliant? Are there factors that might influence this? What are the expected compliance and enforcement levels (alcohol/drugs, speed, road rules, and driving hours)? What is the likelihood of driver fatigue? Can the enforcement of these issues be conducted safely? Are there special road uses (e.g., entertainment precincts, elderly, children, on-road activities, motorcyclist route), distraction by environmental factors (e.g., commerce, tourism), or risk-taking behaviors? General guiding assessment questions for the Vehicle element include the following: What level of alignment is there with the ideal of safer vehicles? Are there factors that might attract large numbers of unsafe vehicles? Is the percentage of heavy vehicles too high for the proposed/existing road design? Is this route used by recreational motorcyclists? Are there enforcement resources in the area to detect non-roadworthy, overloaded, or unregistered vehicles and thus remove them from the network? Can the enforcement of these issues be conducted safely? Has vehicle breakdown been catered for? General guiding assessment questions for the Post-crash care element include the following: Are there issues that might influence safe and efficient post-crash care in the event of a severe injury (e.g., congestion, access stopping space)? Do emergency and medical services operate as efficiently and rapidly as possible? Are other road users and emergency response teams protected during a crash event? Is there provision for e-safety (i.e., safety systems based on modern information and communication technologies)?

Long Description. A scale from 0 to 6 where 0 represents ‘Based Primarily on Expert Judgment,’ 6 represents ‘Based Primarily on Empirical Data,’ and 3 represents ‘Based Equally on Expert Judgment and Empirical Data.’ This guideline ranks a 3 on the scale.

Discussion

The Complete Streets approach can use many different roadway implementations to achieve the goal of an unbroken multimodal network. Applying these assessment frameworks within a Complete Streets project can help designers identify or prioritize network implementations that are associated with desired safety outcomes and select appropriate metrics for ultimately assessing safety outcomes (4). In addition, evaluating road systems from a human factors perspective by considering the interactions between the roadway and road user that contribute to crashes serves to meet the holistic roadway design intentions of Complete Streets and Safe System Approaches, including the mitigation of crash potential on roadway systems and provision of redundancy so that multiple parts of the roadway mitigate crash potential (2, 5).

Safe System Assessment Framework. This framework has four steps: (1) Assess Objectives, (2) Project Context, (3) Safe System Matrix, and (4) Treatment Hierarchy, which are described in detail along with key questions to guide the practitioner in Austroadʼs Safe System Assessment Framework report (1). A key part of the framework is to conduct a risk assessment of common crash types at the project site based on exposure, likelihood, and severity. Reducing any one of the risk factors translates directly into the elimination of fatal and serious consequences related to the examined crash types (1). The factor definitions are as follows:

Road user exposure. The existing or intended road user modes, characteristics, numbers, and the amount of time when they can be exposed to a potential crash (e.g., time traversing along or lingering within the project site) (1).

Crash likelihood. Factors that affect whether a crash occurs. These include design elements that influence conflict opportunity in space (e.g., number of conflict points, separation between modes or opposing traffic) or time (e.g., priority/signals/movement ban), interact with driver human factors (e.g., speed, sight distance, geometric alignment, signs and guidance), or vehicle factors (e.g., road maintenance) (1, 5).

Crash severity. Pre-, during-, and post-crash factors that affect post-crash survivability (5) and injury severity. These relate to the values of the impact speeds, forces, and angles between road users and the presence of roadside hazards (1).

These factors are evaluated within a Safe System Matrix for major crash types against the exposure to that crash risk, the likelihood of it occurring, and the severity of the crash should it occur, using metrics such as the ones suggested in the Design Guidelines table. The levels of these metrics are then translated into a categorical score (out of 4). The exposure, likelihood, and severity scores are then multiplied for each crash type (i.e., by column). The resulting products are then summed across the columns. The closer the total is to zero, the more the overall project aligns with Safe System principles (1). The Safe System Matrix also includes guiding questions for qualitatively evaluating the project against road user, vehicle, and post-crash care Safe System elements (1).

Design Considerations

Interactions between exposure and likelihood. The increased presence of bicyclists and pedestrians also has positive safety implications. The likelihood of bicyclist injury and fatalities decreases as the number of bicyclists increases (6). In an analysis performed by the City of Copenhagen in their 2002–2012 Cycle Policy report, they found that a 40 percent increase in bicycle-kilometers traveled corresponded to a 50 percent decrease in seriously injured bicyclists (6). Likewise, the likelihood of pedestrian injury and fatality falls as more pedestrians are present due to raised driver expectations for encountering vulnerable road users (6).

Cross References

A Framework for Selecting Complete Streets Implementations

Key References

KEY REFERENCES FOR COMPLETE STREETS DESIGN INFORMATION

Introduction

The MUTCD and AASHTO Green Book allow for or encourage flexibility that practitioners can leverage to support broader Complete Streets objectives. Strict adherence to standards can help practitioners minimize liability concerns and skip design exception processes; however, this approach often results in designs that prioritize vehicle mobility over vulnerable road user safety and access and/or misfit a communityʼs context (1). These recommended resources listed in the design guidelines are intended to help practitioners find Complete Streets guidance relevant to their project (complete reference information for these resources can be found in Chapter 28: References).

Design Guidelines

Resource 3-star rating of rigor: ★ ★ ★ Consistently cites guidelines or original research and provides supporting examples ★ ★  Does not consistently cite guidelines or original research, but provides supporting examples ★   Does not consistently cite guidelines or original research; is based primarily on authorsʼ judgment Achieving Multimodal Networks: Applying Design Flexibility and Reducing Conflicts (Porter et al., 2016) | ★ ★ ★ Guidelines and case studies related to applying national design guidance flexibility to address common roadway design challenges and barriers. Focuses on reducing multimodal conflicts and achieving connected networks. AASHTO/MUTCD compliance discussed in “Context for design flexibility and reducing conflicts” section. NCHRP Research Report 1036: Roadway Cross-Section Reallocation: A Guide (Semler et al., 2023) | ★ ★ Guidelines, case studies, measures, and tools related to identifying, comparing, evaluating, and justifying context-based cross-sectional reallocations of urban and suburban roadways for multimodal safety, access, and mobility. Small Town and Rural Multimodal Networks (Dickman et al., 2016) | ★ ★ ★ Guidelines and case studies related to multimodal facilities in small town and rural community contexts. Road Diet Informational Guide (Knapp et al., 2014) | ★ ★ ★ Guidelines and measures related to Road Diet conversions. Road Diets convert an existing four-lane undivided roadway segment to a three-lane segment consisting of two through lanes and a center two-way left-turn lane. Designing Walkable Urban Thoroughfares: A Context Sensitive Approach (ITE, 2010) | ★ ★ ★ Guidelines on how to apply AASHTO guidance to urban roadway improvement projects to meet community objectives. AASHTO compliance discussed in “Differences from Conventional Practice” section. NCHRP Research Report 880: Design Guide for Low-Speed Multimodal Roadways (Elizer et al., 2018) | ★ ★ ★ Guidelines, case studies, and measures related to design of and multimodal conflicts on low- and intermediate-speed roadways. AASHTO/MUTCD compliance discussed. Improving Safety for Pedestrians and Bicyclists Accessing Transit (Goughnour et al., 2022) | ★ ★ ★ Guidelines and case studies on planning and designing transit stops, multimodal access, and transit access safety issues. City Limits: Setting Safe Speed Limits on Urban Streets (National Association of City Transportation Officials, 2020) | ★ ★ Guidelines, case studies, and measures related to urban speed management strategies using a Safe System Approach. MUTCD design flexibility discussed in “Analyze Existing Conditions” section. Urban Street Design Guide (National Association of City Transportation Officials, 2013) | ★ Guidelines, case studies, and measures related to innovative urban street design practices from US and Canadian cities that aim to be safe, sustainable, resilient, multimodal, and economically beneficial, while accommodating traffic. AASHTO/MUTCD discussed in “Relation to Other Nation, State, and Local Design Guidelines.” Transit Street Design Guide (National Association of City Transportation Officials, 2016) | ★ Guidelines, case studies, and measures related to transit facilities and supporting road usersʼ access to transit. Guidebook for Measuring Multimodal Network Connectivity (Twaddell et al., 2018) | ★ ★ ★ Measures and case studies related to evaluating the ease and safety of travel for different modes within a network. Evaluating Complete Streets Projects: A Guide for Practitioners (Seskin et al., 2015) | ★ ★ ★ Measures and case studies related to evaluating access, safety, and equity in Complete Streets projects. Guidebook for Developing Pedestrian and Bicycle Performance Measures (Semler et al., 2016) | ★ ★ ★ Measures for performance management. Measures and metrics used to capture the current state of the system, to set targets to improve performance, and to evaluate and compare the effects of proposed projects and policies. Complete Streets from Policy to Project: The Planning and Implementation of Complete Streets at Multiple Scales (Slotterback and Zerger, 2013) | ★ ★ Case studies and best practices for Complete Streets from jurisdictions in 11 locations across the United States.

Long Description. A scale from 0 to 6 where 0 represents ‘Based Primarily on Expert Judgment,’ 6 represents ‘Based Primarily on Empirical Data,’ and 3 represents ‘Based Equally on Expert Judgment and Empirical Data.’ This guideline ranks a 3 on the scale.

Discussion

In contrast to conventional road design approaches, these guidelines advocate for a shift in the methods and priorities used to determine the following design controls:

Design speed. A concern with using observed driver behavior (e.g., the 85th percentile method) to set speed limits is that this practice leads to speed limit creep (2). Designing facilities for a target speed can encourage operating speeds that reflect safety goals (1, 3, 4, 5).

Design vehicle. Rather than designing a multimodal facility for the largest vehicle expected to use the facility, these guidelines tend to promote using dimensions that represent vehicles expected to use the facility most frequently (i.e., the design vehicle). This approach allows practitioners to select narrower lane widths and smaller curb radii to facilitate reduced speeds and pedestrian crossing distances (1, 3, 4, 5) but also necessitates the allocation of other streets within the network for larger design vehicles such as transit and freight (4).

Functional classification. Increased granularity in functional classification categories can reflect land-use context beyond traditional rural, urban, and suburban classifications (3, 4, 5).

Adjacent facilities to the right-of-way. Multiple uses of shoulder space can encourage on-street parking and accommodate bicyclists or disabled vehicles (e.g., 1, 4).

A practitioner may use these recommended materials to supplement proven crash prediction and reduction tools and resources [e.g., FHWAʼs Interactive Highway Safety Design Model (IHSDM), CMF Clearinghouse, and AASHTOʼs HSM].

Design Considerations

Practitioners should keep in mind that although the FHWA recognizes external guidelines, including many of the resources listed here, as useful references for informing multimodal transportation solutions (see 6, 7), these resources do not necessarily comply with federal laws and regulations (7).

Each resource in the Design Guidelines table includes a 1-star, 2-star, or 3-star rating of rigor based on the documentʼs use of citations and original research and a note on whether it discusses or leverages AASHTO guidelines and the MUTCD. Almost all these documents cite AASHTO guidelines and/or the MUTCD, but only a subset discuss AASHTO guidelines and/or MUTCD compliance. In addition, all of the recommended resources were published prior to the release of the 2023 MUTCD, so a documentʼs stated compliance may not reflect its current compliance. In any US-based project, the jurisdiction implementing a Complete Street is responsible for ensuring compliance with laws, regulations, and standards such as the MUTCD, the ADA, and the completion of appropriate design exception processes (7).

Cross References

Speed Perception, Speed Choice, and Speed Control, Chapter 14

Pedestrians, Chapter 24

Bicyclists, Chapter 25

Key References