Integration of Resilient and Complete Streets in Geometric and Roadway Design Guides

1. Questions

Transportation networks across North America, particularly in urban environments, have slowly begun shifting away from auto-centric infrastructure towards multimodal, sustainable, and safe transportation for all road users. This is often accomplished through a Complete Streets design philosophy and redesigning roadways (LaPlante and McCann 2008; Burden and Litman 2011; Jordan and Ivey 2021). Alongside this emergence, transportation resilience, which we define as the ability and capacity of transportation systems and associated infrastructure to mitigate, prepare for, respond to, and recover from acute shocks and chronic disruptions, is gaining priority to manage ongoing disruptions from climate change and human-caused disasters (Markolf et al. 2019; Sharifi 2019; Wong 2020; Fields and Renne 2021). However, priorities and designs for Complete Streets might not readily align with some transportation responses in disasters, such as evacuations. Moreover, it is unclear how resilience is currently considered in road design manuals, especially those that incorporate Complete Streets designs. Building off Fields and Renne (2021), which investigated resilient streets, we ask two questions in this research:

1. How is resilience embedded in geometric and roadway design?

2. What Complete Streets designs produce co-benefits of safety and resilience?

2. Methods

Focusing on North America, the data was sourced from geometric design guides and roadway design manuals from nine provinces in Canada, nine disaster-prone states in the United States, and four leading transportation organizations in North America^[1]. A content analysis of these design documents was conducted through a keyword and content search of Complete Streets topics (n=12) and resilience-based topics (n=11). The design manual for Quebec was not used since it was only available in French. Table 1 lists each design document analyzed while Table 2 lists and describes all keywords used.

To answer the second question, we conducted a simple analysis of common Complete Streets design measures (e.g., horizontal deflection, roundabouts, etc.) and their interaction with resilient transportation goals. The effects of each Complete Streets measure were brainstormed and listed, helping us identify co-benefits, neutral points, and tensions. While rudimentary, this simple methodology of document review, topical analysis, and goal-comparing can be easily replicated for other geographies to establish a current state for resilient and safe roadway design.

3. Findings

We first present the results of the keyword search and content analysis through average topic frequency for Complete Streets topics and resilience topics by jurisdictional group (Figure 1).

Figure 1.Average Topical Frequency for Resilience (n=11) and Complete Streets (n=12) across Jurisdictional Groups.

Across design documents, resilience topics were much less frequently mentioned than Complete Streets topics. For example, just 14% of all resilience topics were found on average in Canadian documents, while just 28% of all resilience topics were found on average in U.S. documents. We also found that the leading transportation organization design manuals on average had the highest Complete Streets topic frequency, but the lowest resilience topic frequency. Results presented in Figure 1 also suggest that Canadian provincial design documents lag behind disaster-prone states in the U.S. in both resilience and Complete Streets design. Ultimately, we find a lack of prioritization of simple resilience topics (mostly disaster types) across roadway design manuals across all jurisdictions.

We next analyzed topical frequency for Complete Streets and resilience across all design manuals (Figure 2). Despite the high frequency of Complete Streets and sustainability topics, multiple concepts were present in less than 40% of manuals. Under-represented topics included: transit-oriented design, Vision/Target/Road to Zero, land-use change, target vs. design speed, and the Complete Streets term itself. This appears to indicate that road design manuals still focus predominately on larger geographic areas, while more localized concerns and planning (e.g., land use, transit, Vision Zero) are left to individual communities. Focusing on broad topics, over 70% of documents discussed bicycling, traffic/road safety, and vulnerable/all users, indicating a prioritization of alternative modes and equity.

Figure 2.Overall Topic Frequency across 22 Road Design Documents

Relative to Complete Streets topics, resilience topics were largely left out of design guides apart from a few exemplary documents (e.g., Oregon, Washington, California, and British Columbia). Though topics such as flooding, disasters / hazards / emergencies, and climate change were somewhat common, they appeared in less than 50% of all documents. A common disaster across most jurisdictions, flooding was often discussed in the context of drainage needs and its rapid effect on roadway functionality. Other hazards were more jurisdiction-dependent. Evacuation routes, evacuations (other than routes), and the concept of resilience itself were present in less than 15% of manuals.

Standout examples in the U.S. included Oregon’s Highway Design Manual with 82% of resilience topics and 83% of Complete Streets topics, Washington State’s Design Manual with 100% of Complete Streets topics and 36% of resilience topics mentioned, and California’s Highway Design Manual with 82% of resilience topics and 75% of Complete Streets topics discussed. In Canada, British Columbia’s Supplement to TAC Geometric Design Guide mentioned 64% of resilience topics and combined with TAC, mentioned 75% of Complete Streets topics. These exemplars offer a template for effectively incorporating both resilience and Complete Streets topics within design documents for current and future roadways.

To conclude, we conducted a brief examination of the resilience of several Complete Streets design measures (Table 3) for future research purposes based on information provided by several design documents. Overall, few Complete Streets measures appear to directly conflict with resilience goals. Some potential co-benefits include:

• Using transit or bike lanes as flexible lanes during evacuations;

• Maintaining intersection throughput during a power outage via roundabouts; and

• Modal shift and improved safety conditions for walking or bicycling in a disaster.

Most tensions we found involve the reduction of roadway capacity, which could inhibit auto-based evacuations. Temporary infrastructure and operational strategies might be needed to overcome this specific tension, though more research and post-disaster assessments will be necessary.

Although a simple analysis, our study presents a first step into understanding the current state of Complete Streets, resilient roadway design, and the connection of these topics. Future research will be needed to better incorporate sustainability in tandem with resilient street design, managing tensions and promoting co-benefits as transportation networks continue to evolve.