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FHWA Reduces Barriers to Flexible Street Design

Oct 14, 2015
Dec 14, 2017

Big news out of the Federal Highway Administration (FHWA) last week!

On October 7, 2015, the agency announced that it is proposing revisions to current oversight policies that could have a huge impact on how roads are designed in communities. To encourage the design of roads that are more in line with the social, economic, and environmental needs of communities, these revisions will reduce the number of Controlling Design Criteria - from 13 to 2 - for roads designed for speeds of less than 50 mph.

“This proposed policy change will give states and communities the opportunity to be more innovative in designing their local projects,” said U.S. Transportation Secretary Anthony Foxx. “It will help us to build more quality projects that will not only provide more travel options for people, but also support and unite communities across America.”

A street designed for multiple uses and users in Cambridge, MA | Photo by Dylan Passmore

What are “Controlling Design Criteria”?

To fully understand the significance of this announcement, it is important to understand what CDCs are and how they relate to design standards.

Road design is a complex process, involving trade-offs between safety, community and environmental impacts, and project costs. All roads in the US are designed using an assortment of design manuals at the federal, state, and local level. The ultimate standard reference is the American Association of State Highway and Transportation Officials’ (AASHTO) A Policy on Geometric Design of Highways and Streets, which is commonly referred to as the “Green Book.”

Technically, engineers are only required to follow the Green Book for federally funded projects on the National Highway System, which makes up only 4% of our country’s roads. But the use and impact of this manual extends well beyond these roads. Since few communities have the will or resources to create their own manuals, and since state DOT manuals are based largely on the Green Book, it has essentially become the default guide for roadway design around the country.

In 1985, FHWA established 13 controlling design criteria because of their perceived impact on operations and safety. These applied to all projects, regardless of the road’s function or community context.

To ensure consistency in federally-funded road design, FHWA also created a design oversight process that includes special documentation -  called Design Exceptions -  for designs that cannot achieve one or more of the standards. However, since the Green Book contains over 500 pages of design guidance, FHWA’s move to prioritize 13 of these to Controlling Design Criteria made sense at the time, but  it had several unintended consequences.

Fearful of liability, most state and city DOTs discouraged Design Exceptions by making the process difficult and traumatic. While some planners and engineers came to view needing a design exception as an admission of failure, others would go to extreme lengths to ensure that their designs would not require an exception - mistakenly believing that this could expose them to personal liability. Taken together, these concerns led to a culture of ultraconservatism within the field, which in turn led to a surge of over-engineered, community-damaging designs: Trees were cut down, homes relocated, and Main Streets began to look like Interstates.

An unnecessarily wide local road in Fairfield, CT | Photo by Sam Goater
An unnecessarily wide local road in Fairfield, CT | Photo by Sam Goater

With these policy changes, however, FHWA is moving even closer to PPS’s vision for “place-led design,” where communities and transportation agencies jointly create a vision for a place, and then use sound engineering judgment and the flexibility provided in design manuals to create livable, safe, and context-sensitive solutions. These proposed revisions are just the latest in a long list of policy amendments, improved training, and design manuals that have emerged within the last two decades. (PPS has advocated for these principles for many years: See our Guide to Rightsizing Streets as well as our Citizen’s Guide to Better Streets, which offers information and guidelines to help communities work with designers.)

The 85% reduction in the number of CDCs represents a bold step in the shifting of federal culture, from one of rigidity and apprehension to one that promotes openness and flexibility. With only two criteria left - selection of design speed and design-loading structural capacity – designers will face far fewer barriers to creating truly context sensitive design. Other benefits: construction maintenance will be cheaper, and roads will be safer.

“This is truly a landmark moment in the history of road design,” commented Gary Toth, PPS Director of Transportation Initiatives. “I predict that twenty years from now, we will look back at this proposal as triggering the tipping point for sensible Context Sensitive Design.”

Want to help push the movement forward? Read more about the proposed policy update here, and show your support by submitting favorable comments on the US Federal Regulations site before December 7th!

Contributed by Gary Toth and Sam Goater

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