Urban streets serve a much different purpose than rural ones: They’re for walking, socializing, and local commerce, not just moving vehicles. Unfortunately, American engineering guides tend not to capture these nuances.
That can lead to a lot of problems for cities. Wide roads appropriate for rural areas are dangerous and bad for local businesses in an urban setting.
But there’s change on the horizon. The American Association of State Highway and Transportation Engineers’ “Green Book,” the so-called bible of transportation engineering, has some new competition specially designed for urban places.
Last month, the Federal Highway Administration gave its stamp of approval to two new engineering guides: the National Association of City Transportation Officials’ bikeway design guide, which features street treatments like protected bike lanes, and Designing Walkable Urban Thoroughfares: A Context Sensitive Approach, designed to help cities build streets that are walkable and safe for all users.
The urban thoroughfares guide, produced by the Institute of Transportation Engineers and the Congress for the New Urbanism, is based on the concept of “context sensitive solutions,” which seeks to balance the movement of vehicles with other objectives, like promoting active transportation and fostering retail businesses. Both guides are now recommended by FHWA as companions to AASHTO’s guide.
Jeffrey Tumlin, a consultant with Nelson\Nygaard and an adviser to the development of the urban thoroughfares guide, said the revolutionary thing about it is the engineering guidance about the important ways urban “arterials” differ from rural highways. Problems can arise when the Green Book is applied to cities because it is written by the organization of state DOTs, which are mainly concerned with highway building, not local streets.
“While AASHTO guidelines do accommodate a broad array of street designs, where they are weak is providing designers with information about the way in which local streets are very different,” said Tumlin. “Engineers need more thorough guidance on the ways in which urban arterials are distinct from rural highways and ways in which to design those arterials to prioritize a wide variety of objectives.”
The new ITE guide instructs engineers to “use performance measures that benefit all modes,” and to consider the surrounding area — the character of the community — when designing streets.