Greater Greater Washington


DDOT needs clear guidelines for pedestrian design

DDOT will spend much of its road stimulus money to completely reconstruct several roads, including Sherman Avenue, which we discussed recently. Another is 18th Street NW, from Massachusetts Avenue to Florida Avenue, in the Dupont Circle neighborhood. The 18th Street design contains some significant pedestrian improvements, particularly bulb-outs at many corners. DDOT engineers worked hard to design these improvements. Unfortunately, without clear principles for deciding when bulb-outs are appropriate or not, many of the key decisions came down to the last moment with little information.

Many parts of 18th are in bad shape, and WASA needs to completely replace a water main underneath the street. DDOT will rebuild all of the curbs, redo all sidewalks, tree boxes and streetlights, add bicycle parking and sharrows, and place multi-space parking meters along the metered sections. They will also create bulb-outs at many of the corners, which narrow the distance for pedestrians to cross by extending the curb in front of the parked cars.

Proposed design of 18th and T including bulb-outs and bicycle sharrows. (North is to the left.)

The project team worked very hard to keep almost all of the grassy triangles at 18th and New Hampshire. Right now, neighbors plant flowers in those small areas, but the curb ramps aren't ADA compliant. Initially, DDOT engineers proposed considerably shrinking the size of those triangles, but found ways to adjust the ramps and comply with requirements while only removing small pieces of the green space.

Proposed design of 18th and Corcoran. (North is to the left.)

Between one presentation and the next, the team suddenly changed the curb at the southeast corner of 18th and S Streets to have a much larger turning radius. Instead of a sharper corner with two ramps, that corner (at the upper right in the below drawing) has one larger diagonal ramp. What happened?

Proposed design of 18th and S. (North is to the left.)

I asked DDOT engineers about this at the meeting. They explained that unlike other corners like 18th and T, traffic heading northbound (moving left in the picture) hugs the curb since there is no parking lane, and therefore vehicles need a larger radius to avoid swinging into the opposite lane on S as they make the turn. Perhaps, but why so large, I asked? The corner of 18th and Riggs, where cars would turn onto a much narrower street, has the sharper corner.

DDOT engineers made time to meet with me one on one. They explained that the AASHTO guidelines call for a larger radius when two more major roads meet, unlike at Riggs which is a less heavily used road. However, they added, AASHTO guidelines also allow for some flexibility, and they could sharpen the corner somewhat. Since large numbers of pedestrians walk through this corner, which is the southern end of the 18th Street commercial strip, designing it to let vehicles swing around the corner turn without slowing is the wrong design principle.

After presenting my concerns, the DDOT representatives told me that they would modify the corner to use a smaller turning radius. I'm very glad they agreed to this change, as it's the right choice. However, is it really right to make this decision after talking to one resident? What if another resident had met with them and asked for a larger radius that encouraged faster vehicle traffic at another corner?

We need objective standards to make these decisions. The newly-finalized pedestrian master plan does address these issues, though in a general way. The section on turning radii contrasts the standard AASHTO manual's recommendations, which suggest radii wide enough for all vehicles to "turn easily," and the newer IT Context-Sensitive Solutions manual, which recommends radii wide enough for common vehicles but not necessarily all, and making walkable urban intersections as compact as possible.

The Master Plan recommends updating DDOT's policies to match these best practices. It also addresses bulb-outs, also known as curb extensions, writing, "DDOT should develop a policy describing when curb extensions should be installed as part of retrofit projects, rehabilitation projects, resurfacing projects, and new construction. It is generally recommended that curb extensions be utilized to shorten crossing distances and to enhance the public space or to provide space for a bus shelter wherever possible on arterial roadways and at multi-legged intersections."

Having no policy really complicated the debate over this 18th Street project. The original plan contained bulb-outs at most corners with on-street parking. Some residents and ANC commissioners loved the bulb-outs, while others raised concerns. Would these hinder delivery trucks, which generally double park at the corners? Would they be more dangerous for bicyclists? Are they even necessary?

Bulb-outs are a good design practice for pedestrian safety. And according to bicycle advocacy groups, they are not bad for bicycles, as long as they don't block bicycle lanes or anything like that. In fact, by slowing traffic and forcing cars to turn carefully, they enhance safety. During the debates at community meetings and ANC meetings, though, I made these points, but DDOT generally did not. One ANC commissioner asked if DDOT could bring an expert in bulb-outs, to help differentiate those corners where they are valuable from those corners where they might prove a nuisance.

In the end, the ANC voted to approve bulb-outs along the commercial area, but reject them farther south. The DDOT project team promised to follow the ANC's decisions. But the engineers must have felt bulb-outs were appropriate from the start, since they included them. It's important to listen carefully to residents and neighborhood leaders, who can often point out specific local conditions that should bear on the project decisions. But choose to include or reject bulb-outs is too important a decision to leave entirely up to an ANC vote, especially when the ANC couldn't get the information it wanted about bulb-out best practices to inform its own decision. It's even less appropriate to leave it to the last resident who happens to bend the ear of the project team.

DDOT needs detailed policies on bulb-outs, turning radii, and other street design features. Those policies shouldn't become straitjackets that prevent professionals from deviating from a design where it's important, but neither should the designs depend simply on the luck of the draw for the project engineers, ANC commissioners, or vocal residents. When they do, as on 17th Street, each project ends up cutting feature after feature until we end up spending millions to change very little at all. Fortunately, on 18th, we ended up only cutting half of the changes. Hopefully the ANC made the right choice. Right now, we really don't know.

David Alpert is the Founder and Editor-in-Chief of Greater Greater Washington and Greater Greater Education. He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He loves the area which is, in many ways, greater than those others, and wants to see it become even greater. 


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Thanks DA. What are bicycle sharrows?

by Bianchi on May 22, 2009 1:35 pm • linkreport

I've added a link in the story as well.

by David Alpert on May 22, 2009 1:44 pm • linkreport

Surely DDOT already has a policy for street re-design?

Whatever is the case, these re-designs should be scrutinized carefully to ensure they don't create cyclist kill-zones. The new format of 18th and Columbia deliberately directs traffic across bike lanes. In these places the line marking the bike lane is dashed, to indicate that cars should drive into it at that point. But is it a bike lane if motor vehicles must drive through it? No, it's a kill-zone.

I don't know what role WABA played in discussing the plans for 18th and Columbia, but it seem to be a colossal failure of oversight. I'll be looking at the plans for the other junctions of 18th Street and sending comments to DDOT myself.

by renegade09 on May 22, 2009 3:01 pm • linkreport

renegade09: Do you have a link to a plan that shows what you're worried about? Is it on this diagram? There is a dashed line on the bike lane in the center.

Cars need to cross a bike lane before making a turn. It's safer if they cross or enter a bike lane. Otherwise, if a car tries to turn across a lane while a cyclist is going straight, you can get a "right hook" which is the most dangerous kind of auto-bicycle crash. It's not clear to me how that design could be better.

by David Alpert on May 22, 2009 3:06 pm • linkreport


Yes, one kill-zone is clearly marked on the diagram you link to. The other, on Columbia Road north of 18th St, is not indicated, because the bike lane is not marked on this diagram (were these cycle lanes added as an after-thought??)

It's clear to me that the status quo was safer (for cyclists anyway, the new configuration is probably more convenient for pedestrians). It's is not such a stretch to imagine safer options that what we got. The elimination of the right turn lane for traffic headed south on Columbia Road offered an excellent opportunity to add a separated cycle lane that would offer cyclists real protection. For a cyclist heading south from Columbia Road towards Woodley Park (e.g. me, every morning), there are now 2 potential sites where motor traffic turning right must cross the cycle lane during the normal flow of traffic to turn right. While changing lanes at this junction, motorists are principally looking for other cars, and I strongly believe it is only a matter of time before we see a fatality at 18th and Columbia. The current layout has in effect made a 'right hook' a normal, predictable outcome of standard traffic flow.

Another possibility would be to have a cycle lane painted directly ON the sidewalk, instituting the on-road/off-road adventure that cyclists in the UK get with their cycle lanes.

Another possibility is to have a 'cycle box' at right turn junctions, moving cyclists directly ahead of motor vehicles to reduce the risk of the 'right hook'.

So I think it's not hard to imagine safer road remodeling possibilities. I don't know to what extent these were pursued with DDOT for the remodeling at 18th and Columbia. Maybe someone from WABA can advise me what they did to ensure cyclist safety at 18th and Columbia? It's too late now anyway. It's hard, I know, because it's difficult to interpret planning sketches until they are actually physically realized. But it's so important that I think it should be pressed harder.

by renegade09 on May 22, 2009 3:38 pm • linkreport

Why do city planners see a need to accommodate people who drive cars that are too large for them to operate skillfully? If you have trouble making the turn, buy a smaller car. Nothing I hate more than some moron in a giant SUV or minivan who can't stay in their own lane.

Imagine this kind of intersection planning: right angles and hard, sharp corners where every two curbs meet. A big speed bump right in front of every stop sign. Speed cameras at every red light, everywhere--to stop those idiots who insist on blocking the intersection. A dedicated green signal for pedestrians that they don't have to share with turning cars.

Oh, hell--while we're at it, why not metal teeth that come out of the road, like at the rental-car lot, in front of every stoplight? You run the red, you lose your tires, a-hole! God, I would love that.

by JB on May 22, 2009 4:05 pm • linkreport

Citing AASHTO standards to defend suburban-style roadway designs within DC is essentially a snow job. AASHTO allows a great deal of flexibility and leeway in matching designs to roadway context. In this case the context is highly pedestrianized, with high bicycle and transit volumes and a roadside that gives perceptual cues for low vehicular target speeds. Therefore, sharper curb radii are in better accordance with the existing context and function of 18th Street.

David's call for more detailed, firmer policy guidance is exactly correct. The newly-released NYCDOT Street Design Manual provides a pretty good approach. It outlines the major policy priorities that should be addressed, while also giving discretion to engineers and designers so that designs can be responsive to context. The Manual says,

For decades, the city restricted itself to a narrow approach to our streets. That has not only created a less interesting and attractive streetscape than New York deserves, but it also led to a riot of design exceptions as developers, business districts, and city project managers have sought to go beyond a bare–bones, utilitarian approach.

By simultaneously broadening our design horizons, establishing clear guidelines, and adopting a new palette of materials, we will create world–class city streets and a more predictable process for all of the public and private entities who carry out work related to our public rights of way.

The Manual lists these policy priorities:
In a city with as many varied and complex conditions as New York, designs must be tailored for the particular needs and opportunities created by the local context, uses, and dimensions of streets. Therefore, the Street Design Manual leaves ample room for choice, and all designs remain subject to case–by–case NYC DOT approval based on established engineering standards and professional judgment, with the safety of all street users being of paramount importance. ...

Planning and designing streets in accord with the goals and principles of this section will contribute to a consistent level of quality and functionality for New York City’s streets. This policy, along with the project's planning framework, should be used to resolve conflicting priorities for limited street space.

Overall goals are:

1 Design for Safety: Move people and goods safely.

2 Design for Access and Mobility: Accommodate all street users, giving priority to the most energy– and space–efficient modes.

3 Design for Context: Respond to neighborhood character.

4 Design for Livability: Create a vibrant public realm with high–quality public spaces.

5 Design for Sustainability: Contribute to a healthier and more sustainable environment.

6 Design for Visual Excellence: Create coherent and harmonious streetscapes.

7 Design for Cost–Effectiveness: Provide the greatest possible value to the public.

by Laurence Aurbach on May 22, 2009 4:28 pm • linkreport

There's absolutely no way I will be using that segment of bike lane at Columbia and 18th [it's actually still Adams Mill Rd at that point I think]. I just can't believe anyone thought it's placement was a good idea.

by ontarioroader on May 22, 2009 4:43 pm • linkreport

"It's hard, I know, because it's difficult to interpret planning sketches until they are actually physically realized. But it's so important that I think it should be pressed harder.

It's also probably one of the biggest impediments to getting residents and other laymen interested in planning and design. Drawings are difficult to read for people not used to the symbols, but visualizations almost always gloss over important details and are instead used to sell projects. Even when you simplify a plan and use colors and nice simple labels, I feel like a lot of people just don't have the visual-spatial skills to get a solid sense of what it looks like.

Anyone who is not an architect or engineer ever been turned off by opaque drawings, or would people still not care?

by цarьchitect on May 22, 2009 5:12 pm • linkreport

I feel like a lot of people just don't have the visual-spatial skills to get a solid sense of what it looks like.

It's part experience, and part lack of education. Where in school do we get taught to interpret maps? Have you ever asked people to draw their living room to scale?

by Jasper on May 22, 2009 8:46 pm • linkreport

@renegade09 I'm having trouble seeing where you're concerned about right hooks. you wrote:

"For a cyclist heading south from Columbia Road towards Woodley Park (e.g. me, every morning), there are now 2 potential sites where motor traffic turning right must cross the cycle lane during the normal flow of traffic to turn right."

Are you talking about the alley and then again at Adams Mill Road? What about 18th and Columbia do you find unsafe?

by David C on May 27, 2009 10:05 am • linkreport

@Jasper, I was taught to interpret maps at several stages in school. We even made a "to scale" model of the neighborhood in 1st grade (using those little milk cartons as houses). I think while certain spatial skills can be learned and strengthened, like so many other things, some people are just better than others.

by David C on May 27, 2009 10:46 am • linkreport

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