One of the foundational documents in our country’s history of car-centric street design is what’s known as the Green Book. These engineering guidelines, which have been published in various editions by the American Association
of State Highway and Transportation Officials (AASHTO) since the 1930s, are only "green" if you’re looking at the cover.
"We should take control of our streets. If 85 percent of our motorists are driving faster than we want them to, then we need to redesign the street."
Inside, the Green Book codifies an anti-urban design approach that transportation engineers have followed to disastrous effect in American cities and towns, creating wide streets where cars rule, speeding is the norm, and the greenest modes of travel have no place. While its recommendations are only advisory, the Green Book is often treated as gospel, implanting ideas like the "85th percentile" standard, which dictates that streets should be designed to "forgive" the 15th-fastest driver out of every hundred on the road. In the words of former Maryland transportation chief James Lighthizer, this is like building streets as though "everyone on the road is a drunk speeding along without a
Fortunately, these engineering standards are shifting. One important step is a new report co-authored by the Institute of Transportation Engineers (ITE) and the Congress for the New Urbanism (CNU). "Designing Walkable Urban Thoroughfares: A Context Sensitive Approach" aims to define a more humane engineering language for streets. The report is intended to supplement the Green Book by laying out a set of design standards that make sense in places where people can get around by foot or on a bicycle.
If, as U.S. DOT Secretary Ray LaHood recently pledged, walking and biking are going to have equal standing with motorized transport, more enlightened engineering guidelines will have to play a significant role. To better understand how the CNU/ITE report can influence state DOTs and the way they shape streets, we spoke to one of the experts who helped develop it, Dan Burden.
As the founder and executive director of Walkable Communities, Inc., Burden travels the country helping people plan and develop more sustainable neighborhoods. In 2001, Time Magazine named him one of the six most influential civic leaders of tomorrow. Burden spent 16 years as bicycle and pedestrian coordinator for the Florida Department of Transportation, so he was able to share with us his experience as both an advocate and an administrator.
Here’s the first part of our interview:
Noah Kazis: Let’s start with that new ITE and CNU report that you participated in. What’s its significance?
Dan Burden: A couple of big breakthroughs occurred with that publication. One where we struggled hard, but finally broke free, is setting a target speed for roads. Before, there was always the driving speed, which had to be higher than the posted speed to provide "forgiveness" to drivers. Of course, drivers totally figured that one out, and they’d drive faster than the posted speed. In these guidelines, they’re supposed to design the road for the speed that we want to elicit from the driver.
NK: Who is the target of this report? Who’s going to be implementing its recommendations?
DB: Any city or county engineer — anyone who is going to be professionally responsible for setting street standards for their own community — will be able to find that now there’s an official resource provided by the Federal Highway Administration that they can pull language from. It is truly an authoritative source. This collective body of professionals got together and agreed upon these new criteria.
NK: Is this a shift for ITE? Many of us think of transportation engineers as very conservative, very car-centric.
"The AASHTO Green Book is built for rural America and for suburban America. It was never designed for downtowns. It was never designed for the average neighborhood street."
DB: It is a shift for ITE. ITE, fortunately, is a little more progressive than the AASHTO, the American Association of State of Highway Transportation Officials, but this is a significant advance. It represents a blending of the transportation industry with the Congress for the New Urbanism. I don’t think ITE on their own would have been quite as bold. But with the leadership of the CNU, they really were able to bring in the best of the engineers.
NK: Besides bringing the posted speed and the design speed into alignment, what are the other innovations in this report?
DB: A lot of language was created to allow a more liberal interpretation of flexibility. We shouldn’t force any given category of street to fall under very tight constraints. We really need permission to build narrower roads, to use less asphalt, to green up the streets, to emphasize the need for walkability and bicycling, to bring down speeds on roads.
We shouldn’t just use some antiquated language that says we have to post the speeds according to what 85 percent of motorists are doing. Instead we should take control of our streets. If 85 percent of our motorists are driving faster than we want them to, then we need to redesign the street, rather than letting the tail wag the dog. There’s something wrong with our street design if you’re getting 85 percent of our motorists to drive 10 miles an hour faster than is safe for the conditions.
The report sets the platform for creating that livability. It covers the planning aspects, it gets into the broad-based principles and then it gets down to the exacting details and explains why 10-foot and 11-foot lanes are superior to wider lanes. It gives more flexibility while providing specific language that an engineer and a planner could pull for their own street standards.
NK: How do these guidelines and recommendations get turned into change on the street? Where does the federal government come in? The state and local governments?
DB: First of all, there’s always been a misunderstanding about federal standards. It doesn’t matter what state I go to; I can hear some folks in the state agency say, "Well we have to do this, because the federal government says that these are the standards." The federal government does not set standards. They help create publications, they provide a lot of guidance, but they truly have no desire or ability to set the standards that a local government would impose.
The key is influencing those in state government to realize that they’re in charge, that whatever language they create can then be inserted in a local street system that happens to involve state funding. In some states, the total street system, from an alley to a lane to an arterial, is set by state guidelines. In Florida, we have what’s called the Green Book committee; I used to sit on it for about 15 years. We came up with guidance for what every category of road would be and then whoever built the road — certainly any private developer — had to follow those standards if they wanted to turn the road over to the community. They gave a baseline for certain margins of safety and performance.
"The clear zone that’s required — how far you have to set back trees or other fixed objects from the roadways — was determined years ago by one phone call from a committee of AASHTO to the General Motors test track."
The problem of having standards that every community in the state must follow is that it doesn’t necessarily give the best level of flexibility. If a community writes their own street design guide, then they can totally revamp: They can come up with flexible streets, curving streets, living streets, all the terms we’re now using. So it becomes imperative to get street making down to a local level. You still need to be predictable at a state level, though. This guide helps give the language that a local community might need to narrow streets or provide a different level of street connectivity. That’s something that needs documentation.
NK: So are you arguing that states should take a step back from transportation planning and let local governments move in?
DB: Yes I am. I feel that the people who end up populating the committees that set these standards are not keeping their ears close enough to what’s going on in a given neighborhood. By the time you’re high enough up in the chain of your state agency, you no longer go to public meetings, you no longer read every document that comes out. So you’re trying to make decisions that are good for everybody, even though you’ve reached a point in your career when you’re no longer grassroots.
NK: What does that detachment lead to?
DB: You feel like you have a responsibility to keep raising the bar but in many cases the bars gets raised with absolutely no scientific evidence. For example, the clear zone that’s required — how far you have to set back trees or other fixed objects from the roadways — was determined years ago by one phone call from a committee of AASHTO to the General Motors test track. So they’re talking to one person at the test track — for cars — and the guy said 100 feet and [AASHTO] said, "No, that can’t work, we can’t buy 200 feet of right of way everywhere." So they negotiated and said 60 feet would eliminate a lot of the crashes. That’s how they determined it. If you went back and studied how a particular measure came to be, it’s, "OK, if I agree with you it should be 15 feet rather than five, then will you agree with me on my point about this topic?"
NK: In terms of the internal politics of state departments of transportation, is there some sort of bias in how the roads are designed?
DB: Historically the AASHTO Green Book, which is still what most people will quote and many state design guidelines are built around, is built for rural America and for suburban America. It was never designed for downtowns. It was never designed for the average neighborhood street. It was designed for this new America we were building, where we wanted to keep the greatest flow of vehicle movement. So we come up with things like turning radii on the corner of an intersection, driveway flows, everything based on a suburban and a rural application.
NK: Do you think that momentum toward livable streets — among both engineers and the state departments of transportation — is going to continue?
DB: I know it’s going to continue. For example, take complete streets. Every state that adopts a complete street philosophy now comes together to try to figure out, well, What does this really mean? So it builds on itself. I was in Columbus, Ohio, where the state has adopted a complete streets package and now everybody is quickly trying to figure out, Do we always have bike lanes or do always have this or that? So, yes, I think that, along with Secretary LaHood’s recent comment that pedestrians and bicycles will have equal considerations in designing and building and funding our streets, that this is shaking up the industry.
Obviously we’re crafting new buzzwords and we’ve got more enlightened secretaries of transportation, but we’re also going to realize we cannot continue to build roads that are not sustainable. They create more drainage impacts, more heat gain, more use of oil for asphalt or processing concrete. These resources are going to put us in a non-compete situation with the rest of the world where we’re just trying to keep our system working. In many cities now the individual is spending 20 percent, even 25 percent, on their transportation out of their take-home pay. That’s not sustainable at a personal level.