Greater Greater Washington

"Lane closed to ease congestion" actually not a crazy fail

Michael sent along this amusing "FAIL" photo... but is it really a fail at all?


Image from FAIL Blog.

At first blush, this looks ridiculous. How can closing a lane ease congestion? But actually, it can.

Let's say you have a road that's one lane in each direction. At one spot, it turns into 2 lanes each direction, then back to 1. What will happen?

People will speed up when the road widens, then merge back where it narrows. Merging creates "friction," forcing drivers to slow down a little more than usual and to wait for each other which can be inefficient. The end result is lower throughput overall than if the road simply stayed one lane.

This exact thing happens on the Clara Barton Parkway. There's an area just outside DC with exactly this geometry. The parkway might flow well until that point, yet during periods of moderate traffic there's always congestion right at the merge.

Sometimes an extra lane is worthwhile. Many mountain interstates widen to provide climbing lanes for large trucks, for instance. But the Clara Barton Parkway is not such a situation (and doesn't allow trucks, anyway).

For a short time I had to drive to Potomac in the evening rush periodically, and always wondered why this bizarre situation still existed. If the parkway simply remained one lane each way with the other closed, it would indeed ease congestion.

Maryland narrowed Bradley Boulevard in Bethesda around where it crosses the Beltway. The road, usually 2 lanes each way, widened to 4 and then narrowed again. Now, 2 whole lanes are marked off with stripes. That smooths traffic and also gives bicycles and pedestrians a better shoulder to use when connecting between neighborhoods on either side.


Bradley Boulevard. Image from Google Maps.

As for the FAIL Blog photo, that was on a highway in Cornwall, England in 2006. Huge numbers of drivers were descending on the region for a music festival, and officials recognized that a 2-mile passing lane would actually worsen traffic with the heavy load.

It may sound barmy but in fact it makes a lot of sense because, if it was left open, traffic from the two lanes would have to merge into one at the top. This causes a lot of aggro and a lot of stopping and starting which has been shown to delay traffic even more.
How about cutting down on the "aggro" on the Clara Barton as well?
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David Alpert is the founder and editor-in-chief of Greater Greater Washington. 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 now lives with his wife and daughter in Dupont Circle. 

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Yup. Similarly, reducing traffic speeds tends to increase overall throughput on congested neighborhood streets (obviously the dynamics are different on an eight lane superhighway).

That's why it's always funny to hear people argue against slower traffic speeds and complete streets: "Congestion! Pollution!" It's a classic case of unexamined common sense trumping reason.

I guess they've never heard that, in a fire drill, you're supposed to walk in an orderly fashion, as opposed to everyone making a mad break for the stairs.

by oboe on Jul 29, 2011 12:28 pm • linkreport

The faster I get out; the more everyone else will be able to walk in an orderly fashion.

by Bossi on Jul 29, 2011 12:31 pm • linkreport

Though this is clearly logical, why is it that road boosters continually perpetuate the myth of 'easing congestion' by widening lanes (such as the ill-fated I-66)? Simple: greed. Instead of using legitimate planners who could quickly identify that the main throughput is only as fast as the area with the fewest lanes, there are heavily subsidized asphalt companies lobbying to state and local leaders about how they "need" to buy more and more extremely expensive asphalt for road construction / expansion projects "in the interest of their constituents". What does need to happen is that we need to balance our roads with rail.

by C. R. on Jul 29, 2011 12:32 pm • linkreport

"Similarly, reducing traffic speeds tends to increase overall throughput on congested neighborhood streets."

Maybe. But how do we get rid of all the unfriendly speed bumps that have cropped up recently in NIMBY strongholds like Cleveland Park? They impede the free flow of traffic. They also send an exclusionary message, and may discourage patrons of new restaurants and retail from wanting to come to the area.

by JBC on Jul 29, 2011 12:48 pm • linkreport

I would like to see this applied to the I-66 / Dulles Access Road junction. I think it wouldn't be a perpetual traffic jam if both roads shrunk to one lane before merging together. Merging two lanes to one should be smoother than merging four lanes to two. There would still be some jockeying for the I-66E cars that need to get over to exit on Westmoreland or 29, but I think the traffic pattern would be safer and more efficient.

Also, why are they building extended "merge" lanes on I-66 inside the beltway. It seems this will just create additional choke points that will disrupt traffic during moderate usage.

by JHH on Jul 29, 2011 1:06 pm • linkreport

I've got a couple more for you: Queens Chapel Road in Hyattsville/Chillum was similarly narrowed and now has center lanes marked off with yellow lines:


View Larger Map

But an area where getting rid of a lane would really do some good is the section of the Outer Loop between where northbound I-95 breaks off and southbound I-95 merges on. After northbound I-95 splits off, the Beltway is a whopping four lanes wide here. Then two lanes of southbound merge, creating a six-lane monstrosity. Drivers originating from the Beltway that want to get off at New Hampshire Avenue northbound have to merge right across several lanes of traffic, and drivers coming from southbound I-95 to the outer loop have to merge left to avoid the exit only lane at New Hampshire. And then a merge lane from southbound New Hampshire ends, then the right lane ends, so there is a huge bottle neck between New Hampshire and University. Eliminating a lane or two on the outer loop prior to the southbound-to-westbound merge would probably eliminate some of that daily headache.

by Dave Murphy on Jul 29, 2011 1:14 pm • linkreport

@JBC:

But how do we get rid of all the unfriendly speed bumps that have cropped up recently in NIMBY strongholds like Cleveland Park? They impede the free flow of traffic. They also send an exclusionary message, and may discourage patrons of new restaurants and retail from wanting to come to the area.

You do it by implementing automated "average speed" enforcement. This isn't limited to Cleveland Park, NW, or the District. Go to any residential cul-de-sac in the suburbs and the residents are *extremely* motivated to get speed enforcement wherever they can.

There are many, many residential neighborhoods in the suburbs where the speed limit is 20 mph. Obviously, most of the folks who drive through them are residents, so they're particularly mindful. The residential neighborhoods in DC see both local and non-local traffic. People tend to not care so much about the safety of neighborhoods in which they don't live. Given the choice between "free flow of traffic" and safety, residents are going to choose safety. Just human nature.

by oboe on Jul 29, 2011 1:19 pm • linkreport

Remember the predictions of the traffic apocalypse that would happen with the closure of those lanes on NY Ave?

And then remember how the lane closures actually increased the number of turning lanes, and improved traffic flow on NY Ave dramatically?

I'm almost hoping that DDOT revises the project, and narrows the road in some sections to preserve those turn lanes, and keep the flow moving.

by andrew on Jul 29, 2011 1:33 pm • linkreport

Oh, yeah. I'm all in favor of narrowing, low speeds in neighborhoods, etc.

But, seriously. F*ck those speed bumps.

Also, let's start trying to reduce superfluous traffic lights. There are lots of 'em in Capitol Hill that would be much more logical as stop signs (or even just changing to flashing reds on non-peak hours). I'm sure other neighborhoods have their fair share of these.

by andrew on Jul 29, 2011 1:35 pm • linkreport

On Capitol Hill, the traffic lights actually make things worse for pedestrians. Unfortunately decades of unexamined traffic control practice have left us with the idea that stop signs are safer than no stop signs, and wherever there's a stop sign, it can be made safer with a traffic light.

Meanwhile, auto traffic treats many of the Hill streets like drag racing strips, as they race from one light to the next, trying to beat the red, oftentimes just running it if they're too slow.

by oboe on Jul 29, 2011 1:58 pm • linkreport

Perhaps not much time should be wasted on trying to correct misconceptions on FailBlog ... among the site's most popular blog posts are pictures of clouds shaped like penises and foreign language words and names that sound like English expletives. So not exactly the most forward-thinking crowd on the Internet.

Though this "fail" is worth a look. http://failblog.org/2011/01/20/epic-fail-photos-classic-l-a-parking-signs-fail/

by Scoot on Jul 29, 2011 2:40 pm • linkreport

@Dave
What's the story on those lanes of Queen's Chapel Road? Are they remnants of an old street car line? I drive each day through that section and the intersection of QC Road and Riggs Road has several cars attempting to make a left turn from QC onto Riggs, but they are cut off by the traffic "cones" installed in the empty lanes.

I would like to see them shift the two existing travel lanes over towards the middle of the road and install bike lanes along the right-hand shoulder. There are a fair number of cyclists in that area riding to and from the metro and river trails.

Alternately, but less ideal, they could install a real median between the lanes with trees to provide shade. Right now the median is full of power lines and telephone pulls, many of which look like they could come down into traffic at any moment. Who's idea was it to install power lines down the median of a four lane road with little to no median?

The empty lanes are wide enough to even build a grade separate bicycle lane in each direction, but who am I kidding. This is Maryland where the car rules, for now.

by Scott on Jul 29, 2011 2:44 pm • linkreport

@Dave Murphy-That part of QC Rd is Mt. Rainier (at least the southern/eastern side, but I think the north as well)
@Scott- QC doesn't intersect Riggs Road. Are you talking about Ager?

by thump on Jul 29, 2011 3:23 pm • linkreport

@thump Sorry, referring to Chillum Rd. If ever there was a stretch of road that could use a bike lane, this would be it:

http://maps.google.com/maps?saddr=Eastern+Ave+NE&daddr=Ager+Rd&hl=en&sll=38.953902,-76.957598&sspn=0.019523,0.037036&geocode=FXRGUgId0mlp-w%3BFVVsUgIdwJVp-w&gl=us&mra=dme&mrsp=1&sz=15&t=h&z=15

You can take the Anacostia Tributary Trail from QC Rd. to the West Hyattsville Metro, but in the winter with snow, the trail is one of the last to be cleared for bikes. The space is already available on QC Rd. for dedicated lanes so it might as well be utilized.

by Scott on Jul 29, 2011 4:50 pm • linkreport

My brother was in one of the massive traffic jams down in Florida during one of the hurricane evacuations a few years back and he noted the same phenomenon mentioned in this article. The people who operate Florida's Turnpike suspended toll collection to help the evacuation (good move), but for some reason they didn't block off all the toll lanes beyond the number of lanes on the highway (bad move). Back then there were no high-speed SunPass lanes. So at every toll plaza, people immediately spread out to use all the lanes only to have to choke back down on the other side. Instant congestion.

A local road that I can think of that widens for no apparent reason is US-50 just west of Middleburg. Not only does it widen, it goes from a two-lane road to a dual-carriageway. There isn't really enough traffic to require a dual-carriageway through there and for the most part the main benefit of that stretch is that it lets the more lead-footed people pass slower traffic. I hear VDOT agrees that the dual-carriageway is unneeded and is going to move all the thru lanes onto one side, narrow it to a two-lane road like the rest of US-50 out there, and make the other carriageway a cul-de-sac design for local access only. Makes a lot of sense to me.

JHH--regarding I-66 and the Dulles Toll Road, I read something recently that said that VDOT is exploring ways to revise the merge there, but I haven't seen anything regarding what they're investigating. I don't think narrowing either road was mentioned, but it's an intriguing idea. As you note, I-66 west of that point is seldom congested. But I think federal highway standards do not allow narrowing an Interstate to a single lane on ordinary mainline pavement like that unless a special waiver is granted by the FHWA (for example, New Hampshire got a special waiver to build I-93 through Franconia Notch as a "super-2" to help protect the Old Man of the Mountain, which later collapsed anyway).

by Rich on Jul 29, 2011 5:32 pm • linkreport

Yes, but would the politicians hearing all the complaints make the traffic engineers reopen the lane to "ease congestion." That would be AMF and Jim Graham's approach; Give the citizens what they ask for, not what makes sense... Can you remember one case in the not too distance past of a such a case within the District? I can.

by Some Ideas on Jul 29, 2011 6:05 pm • linkreport

@ oboe:There are many, many residential neighborhoods in the suburbs where the speed limit is 20 mph. Obviously, most of the folks who drive through them are residents, so they're particularly mindful.

Well not here in my suburb. People speed like maniacs, ignore the 35 to 25 speed reduction, and the police is having a blast ticketing people at the (useless) stop sign.

People care about the 10 feet in front of their house. As soon as they're further than 10 feet from their home, safety be d@mned.

by Jasper on Jul 29, 2011 6:55 pm • linkreport

In the same vein, I wish the construction planners for the North Capitol street construction project would just close the whole lane BEFORE it goes below grade so that some commuters would use the lane that crosses NY and RI ave instead of closing the lane as it goes below these two avenues. The merging is always a clusterfuck.

by Le Fabe on Jul 29, 2011 6:56 pm • linkreport

I would like to see Klingle Road rebuilt as a four-lane connector (aka the "One City Parkway") up through Cleveland Park to the new Giant Cathedral Commons complex. Watch all those NIMBY heads spin around!

by Alf on Jul 30, 2011 11:34 am • linkreport

6th st NW between NY and Rhode Island Ave could definitely use this treatment. Dedicated left turn lanes with one lane through in each direction coupled with properly timed and signed lights ( ie 25 mph = all greens), it would be a great change from the current rally car clusterf**k it is now. Stopping all the merging and lanes changes and the throughput stays the same or even go up.

by Chris R on Jul 30, 2011 12:13 pm • linkreport

I never realized aggro was an actual word out of video games. What the hell does that even mean?

by Doug on Jul 30, 2011 12:13 pm • linkreport

Years ago, the NPS changed the GW Parkway East/Southbound at VA 123 by permanently closing the right lane at 123, allowing traffic from 123 to flow unimpeded onto the parkway. Since then, traffic has flowed much better than before due to the reduced merging there.

That change was inspired by a highway merge in Japan that had a backup on one but not the other leading into the merge. The authority there closed the right lane on the road that was not backed up. Result was to equalize the backup on both roads and increase trough-put by eliminating a zipper merge at rush hour.

So even if there is traffic, overall result is likely better than before for all users on the roads that closed the closure in the photo.

by dcseain on Jul 31, 2011 10:24 pm • linkreport

Well not here in my suburb. People speed like maniacs, ignore the 35 to 25 speed reduction, and the police is having a blast ticketing people at the (useless) stop sign.

People care about the 10 feet in front of their house. As soon as they're further than 10 feet from their home, safety be d@mned.

I agree with this. The street in and out of my neighborhood has a 25-mph speed limit. I usually set my cruise control between 25 and 30 and I get tailgated almost every day. It's not unusual to see people doing 45.

Funny thing is, that street used to have no center stripe. People tended to drive too far to the center and there was a wreck when some fool teen was going too fast and caused a head-on collision. So they put a double yellow line down the middle. People's speeds have gone up in the years since they did that. I wonder if there are any studies about such lines and whether they affect driver behavior. My theory is that the double-yellow might make the road seem closer to an arterial than to a neighborhood street.

(To be clear, there are no houses fronting that street, but there are multiple townhouse and single-family streets, as well as a condo car park, all accessed from it, and a fair number of cars parked on it.)

by Rich on Aug 1, 2011 12:05 pm • linkreport

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