CHAPTER 2

Decision-Making Principles

Practitioners should understand the following principles as they apply this tool and design guidelines for decision-making and implementing designs: The Safe System Approach, Considering Bicycle Design Users in Design Decisions, and Design Flexibility and Engineering Judgment. These principles were used in interpreting the research findings and incorporated into the decision tool and supplemental design guidelines. Each of these principles is described in further detail in the following sections.

The Safe System Approach

The Safe System Approach is recognized as a strategy to reach a goal of zero deaths on roadways by acknowledging that the human body has limited ability to tolerate crash impacts and that human mistakes should not lead to fatalities—ultimately, fatalities and serious injuries are unacceptable. This approach is built off the five key principles illustrated in Figure 3: (1) safe roads, (2) safe road users, (3) safe vehicles, (4) safe speeds, and (5) post-crash care. Intersection designers should prioritize safe interactions between modes and use redundancy in design treatments to reduce the frequency and severity of crashes at intersections. The tool and guidelines developed as a part of NCHRP Project 15-73 strive to provide intersection design guidelines and tools that align with the Safe System Approach.

Considering Bicycle Design Users in Design Decisions

The target bicycle design users play an important role in bikeway selection and selection of intersection treatments. Bicycle design users can be “highly confident” bicyclists, “somewhat confident” bicyclists, or “interested-but-concerned” bicyclists, as shown in Figure 4. It is well understood that greater separation from motor vehicle traffic along streets and at intersections increases comfort for people biking and those driving (Winters and Teschke 2010; McNeil et al. 2015; Sanders 2016; Warner et al. 2017; Abadi and Hurwitz 2018). Providing high-comfort bikeways is an important consideration for communities that are building connected bicycle networks given the demonstrated link between the presence of facilities, perceived comfort, and ridership (Dill and Carr 2003; Broach et al. 2012; Blanc and Figliozzi 2016). Continuity is also important, as people riding bicycles in a separated bike lane prefer to maintain that separation approaching intersections rather than operating in mixing zones with vehicles (Monsere et al. 2020). Thus, intersection design and operation are critical, especially along routes with separated bike lanes, to create comfortable bike networks. There is evidence that the protected intersection design is perceived as safer and more comfortable by bicyclists and potential bicyclists. A 2019 study found that intersection designs that maximize bicyclists’ physical separation from motorists, such as a protected intersection design or signalized separation, are rated most comfortable

(Monsere et al. 2019; Monsere et al. 2020). Further, treatments like green bike lanes and bike signals have been viewed favorably by all road users (Monsere et al. 2015; Rahimi et al. 2013). Even if high-comfort bikeways are implemented along a street, if the protection or buffer does not continue to the intersection (e.g., a separated bike lane transitioning to a mixing zone at an intersection), it may discourage some riders from using the bikeway because of a lower perceived comfort of the user (Monsere et al. 2020).

There are some cases in the decision tool that state that selection of a particular intersection treatment type will affect user comfort and the ability for the treatment to accommodate the interested-but-concerned bicyclist. These decisions are highlighted with a dashed line in the decision tool flowchart.

Designing for the interested-but-concerned bicyclist is intended to accommodate the needs of all bicyclists; however, bicyclists in the interested-but-concerned typology have a wide range of needs to feel safe and comfortable biking. Children biking often have less of an understanding of the rules of the road, are the smallest and least visible bicyclists from the driver’s seat, and have less ability to detect risks or negotiate conflicts with motorists [National Association of City Transportation Officials (NACTO 2019a)]. Similarly, some older adults or people with disabilities might bike at slower speeds or have lower visual acuity or reaction time. Finally, some people who identify as non-bicyclists may bike occasionally or may bike if separated bike lanes are provided. Accommodating the needs of these groups of bicyclists requires an all-ages-and-abilities approach to design, which in higher-stress environments might include prioritizing separation

from motor vehicles at intersections by providing protected corners and eliminating conflicts with motor vehicles and by using traffic signal phase separation or grade-separation. Refer to NACTO’s Designing for All Ages & Abilities for additional details on the design user, how to select bikeways, and the design toolbox for an all-ages-and-abilities network (NACTO 2019a).

The selection of a bikeway design user is often based on a community’s policies or by a project’s goals. Some communities have a planned bicycle network that may identify the intended design user for the overall network or for specific portions of the network. Similarly, a project’s goals might identify the intended design user, or the design user may be inferred based on the stated project goals. Practitioners should understand that designing for the most risk-averse bicyclist (i.e., designing for all ages and abilities) will accommodate the needs of all bicycle design users.

Design Flexibility and Engineering Judgment

AASHTO and FHWA encourage a flexible design approach to street design. AASHTO’s A Policy on Geometric Design of Highways and Streets (The Green Book) (AASHTO 2018) encourages a flexible approach to geometric design, and AASHTO’s Guide for the Development of Bicycle Facilities (Bike Guide) (AASHTO 2012) similarly encourages a flexible approach to designing bikeways. Additionally, FHWA officially recognizes the following NACTO publications for use when designing for bicyclists: Urban Bikeway Design Guide (2014), Designing for All Ages & Abilities (2019a), and Don’t Give Up at the Intersection (2019b). This approach emphasizes the role of planners and designers in determining appropriate bikeway types and design dimensions