Greater Greater Washington


11th Street bridges, part 2: Traffic effects

Part 1 looked at DDOT's ambitious, $500 million project to replace the 11th Street bridges across the Anacostia. The reconstruction will add "missing" ramps and a local bridge, but also more traffic lanes across the river. What will be its ultimate effect?

The Capitol Hill Restoration Society, which opposes the project, hired transportation consulting firm Smart Mobility to analyze the project. At first, DDOT refused to even release their traffic model, but Councilmember Wells intervened to get the data. Smart Mobility found many flaws in DDOT's original analysis. Their model predicts that this project will divert a significant amount of traffic off the Woodrow Wilson Bridge:

Click for larger version.

I colored the freeway diagram based on the map in the Smart Mobility report. Roads in red are those which should see an increase of 300 or more vehicles after the project in the afternoon peak; green roads would see a decrease. (I colored both directions of each road the same; it's possible the morning peak will differ slightly.)

DDOT's response is unconvincing:

It demonstrates that afternoon peak period traffic volumes increase on some links and decrease on other links. In general, traffic increases on I-395 through Virginia and the District of Columbia, and decreases on I-495 and I-295 through Virginia, Maryland, and the District of Columbia. Traffic on most of the local streets does not change or decreases. This is consistent with the Purpose and Need for the project, which is to "reduce the volume of freeway traffic that spills onto the neighborhood streets due to current traffic patterns". ...

[T]eh increase of traffic at the 11th Street Bridges is offset by a decrease in traffic on each of the other Anacostia River bridges. The net increase in daily Anacostia River bridge crossings is only 5 percent.

Moving traffic from the local streets to the freeways is a laudable goal, but the Smart Mobility report doesn't agree that all local streets will benefit. Pennsylvania Avenue, for example, will have lower traffic on the Sousa Bridge, but more traffic on both ends. That's probably because, if the Sousa Bridge becomes less congested from commuters going from the Southeast Freeway to 295, other commuters will start using the bridge.

Even if the project did divert all the traffic off local roads, DDOT's are ignoring all other effects. Moving traffic from local streets to freeways by significantly increasing DC's freeway capacity will also generate a lot more pollution in areas where many people live close to the freeways, especially east of the river. The Bronx has one of the world's highest asthma rates not because of a lot of traffic on local streets, but because it's crisscrossed with freeways.

Finally, the 5 percent increase DDOT expects across the Anacostia River is not a trivial amount. It can make the difference between smoothly flowing traffic and stop-and-go traffic. Just a tiny increase can push a freeway over the edge and cause it to "crash" into slow-moving sludge. The other bridges' reductions offset most, but not all, of the increase in traffic. In other words, we will indeed see more traffic.

More freeway capacity in DC will also move people off of Metro and induce new trips in the long run. The Smart Mobility report claims DDOT hasn't properly modeled induced traffic; DDOT claims they did, but doesn't deny that the project will indeed induce more traffic. They only argue that the original FEIS already accounted for all the damage to DC's air quality that the project will create.

Connecting the "missing ramp" will indeed take traffic off the few blocks right around the interchanges, traffic which today has to exit and re-enter the freeway system. However, DDOT hasn't satisfactorily explained why we can't add in those connections without widening the bridge. The FEIS doesn't present a narrower bridge as an option, for example. In the quest to get traffic off local streets, we'll just end up getting more traffic on some other roads and more traffic in total. The pollution doesn't stay right over the freeway, and spending $500 million to add more traffic doesn't sound like a very smart idea.

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 for the map, David.

It strikes me as odd that the seeming objective of this would be to reduce traffic on the Anacostia freeway south of the bridges - that's the one stretch of freeway within the beltway where an increase in traffic would be OK - since it runs through a sewage treatment plant, a military base, and is substantially separated from the community. You can't say that about 395, either in the District or in Virgina.

This also says nothing about the Potomac crossings - it would seem to me that directing more traffic to the Woodrow Wilson Bridge would be a far better option than trying to cram more onto the 14th St Bridges.

My question is this - is that increase in traffic due to the increase in the bridge capacity or the addition of the missing interchange links? I know you mentioned that DDOT did not consider that alternative, but did Smart Mobility (I've only glanced at the report)?

by Alex B. on Feb 11, 2009 3:47 pm • linkreport

Two things of note.

First, I again question your assertion that this is "significantly increasing DC's freeway capacity". As I explained in Part 1, it isn't.

Second, I'd hazard a good bet that most of the "traffic increase" will take place during off-peak hours, especially with regards to the Wilson Bridge, which has almost no delay during rush hours these days, and will improve even further by the time the Telegraph Rd interchange gets completed (which will be well before the 11th St Bridge project is completed). You might see some people try going through DC during peak hour at first, but when they see the mess that's the SW/SE Freeway during rush hour, they'll go back to the Beltway and the WWB.

by Froggie on Feb 11, 2009 4:41 pm • linkreport

I'm not sure I understand everything that's going on here enough to agree or disagree with your overall analysis, but I think there are flaws with a some of your points.

"if the Sousa Bridge becomes less congested from commuters going from the Southeast Freeway to 295, other commuters will start using the bridge."

It's a net sum zero game. If this is true, then somewhere else will have fewer commuters. This seems to be neither here nor there. People will naturally find the optimum route for their commute, and having more options and more capacity will improve traffic flow.

"Moving traffic from local streets to freeways by significantly increasing DC's freeway capacity will also generate a lot more pollution in areas where many people live close to the freeways, especially east of the river."

This doesn't make sense. Far more people live near local roads than freeways, by definition. While adding new freeways will of course increase pollution somewhat in those areas, it will obviously decrease it by at least as much around the local roads where traffic is alleviated. Pollution is far worse from traffic moving at low speeds, stopping frequently, in congested local areas, than it is from traffic moving on freeways.

"More freeway capacity in DC will also move people off of Metro and induce new trips in the long run"

Do you have any evidence to support this theory? People commute in the most practical way possible. I really doubt that there are thousands upon thousands of people who will suddenly decide to start driving to work if metro works for them now, because the trip takes five minutes less.

The basis of your argument seems to be that we shouldn't improve roadways because it will encourage people to drive more. While I fully favor investing more in public transportation and projects that improve the profile for cyclists, the reality is, we have cars, and car commuting is the only practical option for many people. There are some seriously messed up roadways that need help. If we are to one believed this theory -- of forcing people to use public transportation by neglecting our road infrastructure -- then in your ultimate world I suppose there would be no freeways because that would make car commuting impossible.

But the reality is we need both.

by Jamie on Feb 11, 2009 4:49 pm • linkreport

Froggie: The next part will be addressing your point about increasing capacity.

Jamie: It's not a net zero sum game at all. That's the classic traffic engineer assumption and it's false.

A lot of people make decisions about how to commute every day. A five minute swing will shift some people from Metro to driving. We don't really know how many, but with hundreds of thousands of people commuting, it's not crazy to think maybe a couple percent would shift.

Also, some people telecommute. Some people choose to carpool. Our expansion of freeways always affects these decisions.

Also, people choose where to live based on the transportation options. This is the fundamental driver of induced demand. The research is voluminous. When cities built freeways throughout the 20th century, predicting that a set volume of traffic needed a wider freeway, they instead found that within a few years of the wider freeway, it filled up again. That's because, when the wider freeway came online, people decided they could now live in new, farther-out areas and still get to work in the same amount of time as before.

Traffic does pollute more moving slowly, but it pollutes a lot more by existing in the first place. A fast-moving yet full eight-lane freeway generates a lot more pollution than a slowly-moving four-lane local road. And a traffic-choked eight-lane freeway, which the fast-moving eight-lane freeway eventually turns into, is even worse yet. Again, you assume that there are a set number of people who will drive from set of points A to set of points B, and it's just a network optimization problem. That's not how traffic works in reality because people base whether to commute, how to commute, and where to live based on the options available.

You're right about the summary of my argument. We shouldn't add more freeway capacity (not "improve"; adding more isn't necessarily an "improvement") because it will indeed encourage people to drive more. We have plenty of evidence of that from seventy years of adding roadway capacity all over the nation.

We shouldn't neglect the road infrastructure, but neither should we spend a lot of money (and this is a huge amount) adding a lot more of it.

by David Alpert on Feb 11, 2009 4:59 pm • linkreport

I realize increasing road capacity can potentially increase traffic at some point because of future development. But I doubt it will increase it much because of residents of established, developed areas changing their commuting habits. If you have any references to this effect I'd be interested to read it.

This really isn't the same as adding a lane to I-66 or building a new highway. We're talking about fixing an interchange in the city that's messed up -- not creating new routes from outside. If you are against improving badly designed interchanges, would you be in favor of dismantling or complicating interchanges that actually work well? Where do you draw the line? Is there any situation where you'd favor a change that would improve traffic flow in a congested area? This seems like a pretty impractical position.

by Jamie on Feb 11, 2009 5:08 pm • linkreport

Call me a national security freak, call me a NIMBY, call me a damned fool for actually trying to be a pedestrian in the Judiciary Square neighborhood. I don't mind.

But any proposal that would increase the volume of traffic on the Center Leg is unacceptable. There shouldn't even be a highway there.

by tom veil on Feb 11, 2009 5:15 pm • linkreport

Jamie: Fixing the interchange is a good idea. As I said in the article, there's no evidence that also widening the bridge is a wise investment. If we're going to fix the interchange, we should design the project so that it doesn't draw more traffic across the Anacostia. As much as possible, it should simply get the people who already get off 295, wind around local roads in Anacostia, and then get back on the bridge to stay on the freeway. This project does too much more.

by David Alpert on Feb 11, 2009 5:17 pm • linkreport

We are forgetting that a major benefit to this interchange is the dramatic relief on New York Avenue which is heavily used because the interchange doesn't exist the first place. I would assume this to be the major motivation in building it, not to mention it just makes sense.

by Gunbelt on Feb 11, 2009 6:38 pm • linkreport

I don't love new highways anymore than David does, but IF this came with a New York Avenue road diet AND a removal of 395 to Barney Circle AND transit on the bridge AND better bike connections - I think it could reduce traffic AND make it more efficient. I could live with that. Not that I'm saying that's what's being proposed, but I'd be willing to negotiate.

by David C on Feb 11, 2009 8:37 pm • linkreport

I'm reading and wishing this much intellectual and civil discussion was happening over the current stimulus package - which I'm guessing may in fact end up funding this project?? Too soon to tell...

I am sure DDOT found Smart Moblity's analysis severly flawed too - at least from their response in the Hill Rag.

David C - keep talking and I do believe you may just get your wishes as none of them seem very far off the mark.

I support this project as well as the constructive discussion and I look forward to seeing strong bridges built and maintained between Anacostia and Capitol Hill.

My additional thought is that the plan must incorporate intelligent transportation technologies both in-vehicle and vehicle-to-road side, that will help people make better choices when they get up in the morning, run cleaner transit and private vehicles, move us safer, smarter,faster and more effectively.

I've been challenged in the past few months to embrace change, trust government (with lots of my money) and let go of the past mistakes and that is what I intend to do.

by Biker Mama on Feb 11, 2009 9:40 pm • linkreport

Pollution is ALREADY high east of the river, from all the eastbound SE Freeway drivers idling at the northbound ramp to 295. That area has been a bottleneck for decades because the Barney Circle bypass was never built. But hey, who cares about THOSE people across the river from Capitol Hill, right?

by monkeyrotica on Feb 12, 2009 7:15 am • linkreport


Pollution is SUPER high across the river from AM westbound commuter traffic as well, not just because of the ramp, but because Pennsylvania Ave is too small to handle the amount of traffic it handles every morning/afternoon. Every day = chaotic, standstill traffic, lots of trucks, etc. I don't understand how the district came to the conclusion that Penn Ave can handle any additional load, because it seems ridiculously over capacity as is. David: do you know if the neighborhood around penn ave across the river was solicited for input on this project? I really think they need to figure out how to reduce use on that road, or *sigh* make it larger.

by JTS on Feb 12, 2009 9:36 am • linkreport

I'm still of the opinion that this is a good project.

I commented earlier that I think traffic on New York Ave will decrease significantly west of DC-295, but, although I am more unsure about this guess, traffic could also be improved on Pennsylvania at Barney AND L'Enfant Cir/Minn Ave.

If the 395 tunnel closes (because it will be redundant if the bridges are constructed) a major merge/weave point along the SE/SW will be eliminated possibly improving flow (I realize that still leaves the 14th St bridge and DC-295/I-295 area as merge locations on either end of the SE/SW).

Do we know if the Capitol Police or other security agency support closing the 395 tunnel or record related to this project for "national security" purposes (getting traffic away from the Capitol).

by Transport. on Feb 12, 2009 10:14 am • linkreport

I think overall this is a worthwhile project. Getting from say, Baltimore to points in Arlington/Crystal/Pentagon City area would be greatly improved with this solution. Driving around the beltway and up 395 is very roundabout.

by NikolasM on Feb 12, 2009 10:43 am • linkreport

I don't think there is any question that this project will improve the driving experience for those passing through D.C.

The question is does it make Greater Washington greater? And is it worth the cost.

by David C on Feb 12, 2009 1:11 pm • linkreport

"If the 395 tunnel closes (because it will be redundant if the bridges are constructed)"

Wrong. The Center Leg provides a valuable north south route, and access to the city to the north of the Mall. The 11th Street Bridge project though is a detour into the less affluent areas south of the Anacostia and betrays social justice, particularly without a covering of the Anacostia Freeway.

It would make particular good sense to spread the burden by extending it north (with a bring job east to connect to the north south Red Line corridor and extend as a concrete cut box cut and cover highway alongside CUA/Brookland, rather then the corridor chock disaster now being irresponsibly proposed.

The national security argument would be in favor of extending the highway rather then create a worse traffic bottleneck right in front of Georgetown Law School (which seems to oppose all highways so it is a likely power trip of those jesuitical medievalists.

An terrorist explosion on the surface would do more damage to the Capitol then within the I-395 tunnel, so it would be entertaining to see how they twist up an "argument" to close it on security grounds.

by Douglas Willinger on Feb 12, 2009 3:21 pm • linkreport

Frankly, I can't wrap my mind around the argument presented that this project as stated will induce traffic, so I certainly won't try to refute it. But I think having surface streets cross the Anacostia (in this case, MLK/11th Street) does not add FREEWAY capacity, though it does add road capacity.

I agree with the sentiments that this will reduce traffic on New York Avenue and the 395 tunnel, and eliminate the superfluous Pennsylvania Avenue connection. Since the additional bridge capacity is not freeway, I don't believe it will induce freeway traffic. In fact, I'd be in favor of yet another bridge connecting Massachusetts Avenue across the Anacostia. More street connectivity eases traffic, reduces VMT, and can potentially eliminate car trips. I'm very pleased to see the additional bridge added to the complex... but then again, I'm having a hard time understand thing the induced traffic logic here.

by Dave Murphy on Feb 13, 2009 2:30 am • linkreport

Transport wrote: "If the 395 tunnel closes (because it will be redundant if the bridges are constructed)"

I don't agree at all that the 395 tunnel will be redundant if the bridge connection is constructed. First, using NY Ave and the 395 tunnel to get from Annapolis to Arlington is insane -- connecting from 295S to 395S is much quicker and easier even factoring in the time it takes to get off the freeway and back on -- so it's hard for me to believe that a high percentage of travelers actually use that route.

Second, there are a lot of other routes that the tunnel faciliates. For example, think how hard it would be to get to work without the tunnel if you were a nurse at Children's or Washington Medical Center and lived in Alexandria or Arlington - or Anacostia for that matter. The tunnel is the only quick route into/out of the middle of the city.

And if just the northern portion of the tunnel were closed, as some have proposed, imagine the backups getting onto and off 395 if all the tunnel traffic to and from points north had to get in and out of the tunnel at Mass Ave.

So I don't think the 11st Bridges project will make the 395 tunnel unnecessary. I do support the project, however, because it will eliminate the need for commuters to cut through neighborhood streets because there is no freeway connection.

by JRP on Feb 19, 2009 1:34 am • linkreport

>> "think how hard it would be to get to work without the tunnel if you were a nurse at Children's or Washington Medical Center and lived in Alexandria or Arlington - or Anacostia for that matter. The tunnel is the only quick route into/out of the middle of the city."

You're prioritizing commuters from Alexandria and Arlington over residents who live along N.Y. Ave. As long as the center leg freeway connects to N.Y. Avenue that roadway will remain a pseudo-freeway. Just recently DDOT denied a host of recommendations made by residents to improve pedestrian safety at the intersection of N.Y., 5th and L Streets where a new 55,000sf grocery store opened this past September. They prioritized N.Y. Aves traffic flow over increased pedestrian crossing times which means elderly and pedestrians with shopping carts need to cross 8 lanes of traffic in 20 seconds.

New York Ave could be less like a traffic sewer and more like a grand boulevard if DC played their cards right.

by Paul S on Feb 19, 2009 7:08 am • linkreport

If DDOt wanted balance traffic, they should upgrade NY Ave to an expressway. The tunnel that was proposed to be built from the 3rd Street Tunnel to the bridge over the railroad yards should be built and an interchange constructed at Bladensburg Road. If this were done, traffic would not be encouraged to use the new 11th Bridge ramps. Commuter traffic from US 50 and the BW Parkway would remain on NY Ave and the new ramps would benefit Pa. Ave and East Capitol Street after the East Capitol Street interchange is expanded to include ramps to and from southbound DC 295.

Also, I wonder if DDOT is planning to include extra lanes on DC 295 between the 11th Bridge and the railroad bridge. If not, they will be feed 2 lanes off the 11th Street Bridge into 2 lanes of DC 295. That is were your choke point will happen.

by BSMack on Apr 2, 2009 9:04 pm • linkreport

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