Comments on "Diverging diamond" doesn't help make a walkable corridor - Greater Greater Washington

Comment by Alex

Fri, 04 May 2012 12:17:47 EDT

"Exactly what about the DDI is worse than a standard interchange in the DC area, or more specifically the existing interchange?"

As I understand it, the first DDIs were retrofitted to existing interchanges to gain more capacity. But of course, they didn't gain more capacity than they would have if they had converted the overpassing road to a one-way and routed the other direction onto the next interchange down. Why didn't they do that? Because everyone thinks it's inconvenient to be forced into a detour.

So why would it be "pedestrian-friendly" to force pedestrians to detour to the median? If you are a good traffic engineer, you should understand that each sidewalk should be considered a separate roadway. Forcing pedestrians to cross to the other side is like detouring cars onto a different street.

I agree with MidiMagic, though, that DDIs can be made pedestrian-friendly. To do that, sidewalks should stay on the side, and cars should be made to turn as sharply as possible. There should also be some way of adjusting drivers to local street rather than freeway conditions, whether that is raised crosswalks, signals, etc can be determined by local conditions.

Comment by kk

Thu, 03 May 2012 20:46:57 EDT

@ MidiMagic

Children 12 and younger cross similar streets every single day around this country and around the world. How is this road anymore dangerous than Wisconsin Ave, New York Ave, East West Hgwy, University BLVD, Georgia Ave, Rhode Island Ave, Central Ave, Annapolis Rd, Bladensburg RD etc.

It may be a highway but that means nothing as there are roads, streets and avenues that have the same amount of lanes and speedlimits.

Comment by MidiMagic

Wed, 02 May 2012 09:47:43 EDT

Fixing a typo.

I meant 3 lanes of through traffic in each direction, not six. I went to Google Maps to count lanes, and came back with total lanes instead of lanes per direction. I changed the 4 to a 6 without reading the sentence again.

Any child in the range of 5 to 10 would have the help of a crossing guard when going to school.

Comment by MidiMagic

Wed, 02 May 2012 09:39:00 EDT

Again I repeat: the diverging diamond is not pedestrian unfriendly if it is done right. I would say a regular diamond interchange is much more unfriendly because drivers trying to turn through a gap in 3 lanes of oncoming traffic are unlikely to notice a pedestrian in the far left crosswalk. I remember once going to a job interview in Chicago and having to cross a cloverleaf interchange to get from my hotel (on one side) to the business (on the other side). THAT is pedestrian unfriendly.

Ageist? That's government's idea, not mine. That's how our local child welfare sees it, not me. "A child that young should be accompanied by a parent." I may not agree with it, but that is the (administrative) law here. When kids as young as you stated are found out on the street without supervision, the welfare charges the parents with child neglect. And school districts here are designed so that children do not walk to school across major highways.

Both of those are numbered highways, with six lanes of through traffic in each direction (not counting the turn lanes). And we are talking a quarter mile between the neighborhoods on opposite sides of these roads, with shopping centers and businesses in between. Are young kids going to walk that far? There are schools in the area, but one is a private school, and the other is a middle school (with kids old enough to cross safely).

When I was a kid in the age range you cited, I was allowed to cross any of the two-lane streets in the entire neighborhood, or ride my bicycle on those streets (obeying the vehicle traffic laws of course) once I had turned 8. But I was not allowed onto the highway until I was 12, and then just to cross or walk or my bike across at the crosswalk. The local store was on the other side of the highway. The schools were miles away, so I always rode a bus. If I wanted to visit a friend elsewhere, my parents drove me. This was in the early 1960s.

Comment by Traffic Engineer

Wed, 02 May 2012 09:09:31 EDT

Put my occupation in my "name" so there's no dispute.

Exactly what about the DDI is worse than a standard interchange in the DC area, or more specifically the existing interchange? I think many are hung up on the term "pedestrian friendly". Few interchanges would fit under that header. However, I believe that the DDI is better and safer for pedestrians than almost any other interchange.

The pedestrian crossings are simple, shorter and all but one are under signal control. (the one not usually under signal control is crossing the right-turn from Greenbelt to the freeway ramp, the same condition as just about any other interchange.) Shorter means less time required to cross the roadway, meaning more pedestrian friendly for those walk slower (ie, kids or the elderly.)

So if I had a 5-10 year old, and he/she has been taught how to cross a road, then yes, this would be a LOT safer than what's out there now.

Is it perfect, no, but the perfect solution for pedestrian safety is probably a completely separated path/bridge with no interaction with other modes of travel, and I doubt that'll happen. (And most pedestrians wouldn't use such a facility, especially a bridge if it would require a significant grade change.)

I also disagree with the sub-headline saying vehicles will be faster. Faster in this case implies vehicles traveling at a higher speed. I would instead use the word "quicker" in that vehicles have shorter waits, however the speed for vehicles is lower through the interchange because of the design of the "criss-cross" at each ramp. (Technically, "faster" is accurate but I believe misleading.) Is reducing vehicular congestion bad for pedestrians? I don't think so.

Comment by thump

Tue, 01 May 2012 14:33:56 EDT

@MidiMagic-Isn't that ageist? Why shouldn't a young child be able to walk to the store for a treat OR simply to get to school OR simply to play with friend on the OTHER side of a road? Why? Aren't you just doing Oboe's circular logic thing here...Kids shouldn't be there b/c it's a highway and children shouldn't be on highways?
Also, we're not just talking about kids..I also mentioned older folks. Are they not allowed to cross safely and comfort? In terms of walking pace, seniors and young children are fairly similar. By excluding one, you effectively exclude the other.
What you seem to be saying is "This is a place for cars and vehicular traffic." That's a perfectly valid opinion (though I disagree). However, that isn't what the sector plan is calling for. That community WANTS to be more walkable/bikable. This type of interchange doesn't accomplish those goals.

Comment by MidiMagic

Tue, 01 May 2012 12:18:21 EDT

First of all, a kid that young should not be crossing ANY highway alone. These are highways, not just streets. The age at which a kid is mature enough to cross a highway is usually somewhere near 12.

Second, there is another reason the New Jersey barriers are there. With traffic on the "wrong" side of the road, the low beam headlights, normally turned away from oncoming traffic, are now aimed at oncoming traffic. The barriers stop most of these headlight beams from getting in drivers' eyes.

Comment by thump

Tue, 01 May 2012 12:08:08 EDT

The only real question for me, when it comes to determining whether something could be called "pedestrian friendly", is could a 5-10 year old kid safely cross this intersection on their own. If you think your kid (or your elderly parent(s)/grandparent(s)) would feel safe/comfortable and accommodated using a diverging diamond interchange, than you probably don't walk a whole bunch. If you think a diverging-diamond increases the value of surrounding property, you probably still don't get it. If you think you'd like to visit this place, or find this a pleasant walk/bike to your local coffee hangout, you're kidding yourself.

Comment by MidiMagic

Tue, 01 May 2012 11:49:59 EDT

Nope! I'm a college computer science instructor.

You can't tell how pedestrian friendly something is just by looking at it.

And remember that the photos are of the very first DDI built in the US. We learn from experience.

Look at the DDI in Saint Louis, at the interchange of I-270 and Dorsett Rd. It has sidewalks across the sides of the interchange. They meander worse than the one going down the center (if meandering is a crime). And no way is provided to cross the crossroad, rather than crossing over or under the freeway. At least the original provides a way to get to any quadrant on foot.

Comment by Ian Cooper

Tue, 01 May 2012 10:37:22 EDT

Ooh, I'll play! I guess... MidiMagic. Only a transportation engineer could call that obscenity 'pedestrian friendly'.

Transportation engineers are fast becoming more loathed than politicians. Why do these folks get so much power when they are so obviously incompetent?

Comment by thump

Tue, 01 May 2012 09:28:41 EDT

Let's play a game called "spot the engineer" for this post. Ready. Go.

Comment by MidiMagic

Tue, 01 May 2012 08:46:32 EDT

The only thing pedestrian-unfriendly about it is that an environmentalist has "declared" it pedestrian unfriendly. His "reason"? The pedestrian does not walk in a straight line. And he didn't like the high parapet walls that were between the pedestrians and the vehicles (they were parts of the original bridges, and were left as they were).

The crossings to the center median are under signal control. And since there are no turns at those signals, no turning traffic crosses the pedestrian path.

Those traffic signals must be there. The diverging diamond does not work without them. The right turn ramps can also be signalized if necessary for pedestrians.

It is actually quite pedestrian friendly.

Comment by Ian Cooper

Tue, 01 May 2012 05:48:33 EDT

As a cyclist, I'd actually prefer to ride in the road through the interchange in the video. If I were to ride through the pedestrian 'Death Star' trench, I'd be at the mercy of traffic at every crosswalk. At least in the road I can take the lane and prevent conflicts that way. I think the idea that cyclists will prefer to take the pedestrian route through a DDI is half-baked at best.

Comment by kk

Mon, 30 Apr 2012 22:29:56 EDT

If you want a walkable corridor how about working on the damn transit first then make the area walkable otherwise it is walkable from my residence to my parking space/parking garage to the stores parking lot/garage or streetparking to the store.

You can barely get around PG County on a Saturday outside of Seat Pleasant, District Heights, Oxion Hill, Hyattsville, and some parts of Sultland, Riverdale, Greenbelt. If you dont have a car you dont get around PG County on a Sunday unless you're near a Metrorail Station.

Comment by King Terrapin

Mon, 30 Apr 2012 22:11:56 EDT

While I usually agree with Matt's contribs since they're pragmatic and reasonable, I disagree with this one. Having driven through that interchange many times on both roads the number of peds is probably negligible, which isn't surprising considering the more than half mile distance from Beltway Plaza to the office park east of MD201 with nothing in between.

I think the county should focus on making other more cohesive and densely populated areas nearby more walkable.

*btw another very rare interchange, a continuous-flow intersection, is already located Prince George's County in Accokeek at MD210 and MD228. The main difference between the two is that the Accokeek interchange is at grade.

Comment by Katie

Mon, 30 Apr 2012 19:37:12 EDT

As Joel points out, this interchange is right in between the highly walkable neighborhood of Old Greenbelt and the planned pedestrian environment west of Kenliworth Ave. No, it's not a perfect intersection to start with, and there may not be enough pedestrian traffic to justify improving walkability, but spending lots of money to actually make it worse for pedestrians just doesn't make sense.

Comment by Nic

Mon, 30 Apr 2012 17:56:35 EDT

If there's room, I think we should install roundabouts at the exit ramps somewhat like this. http://www.ourston.com/company/projects/us41.html. This would reduce the roadway width(no turn lanes), make the intersection safer and provide better traffic flow. Ideally, I think we should return it to an at grade intersection preferably with a roundabout like the one at N. Hualapai way in Las Vegas, NV(google map it). Except ours would be little better designed since this one's from 1995. Both roads entering it are 3 lanes.

Comment by Joel

Mon, 30 Apr 2012 17:46:29 EDT

For what it's worth, my wife and I walked along Greenbelt Road from our home in Old Greenbelt (just east of Kenilworth Avenue) to the Beltway Plaza mall (just west) yesterday (4/29), and we passed (or were passed) by at least four other people making the same trek. "Traffic sewer" or not, people do walk this east-west corridor.

Comment by Dave

Mon, 30 Apr 2012 14:56:01 EDT

The narrator is way too dramatic (RED BRICK TREATMENTS!!!111), but there are simple improvements that could have been made there to improve pedestrian conditions. A buffer from the sidewalk to the road, high-visibility crosswalk markings, raised crosswalks through slip lanes, etc. The interchange design, fundamentally, is motor-vehicle-focused. That's the question for 193 here - not whether this interchange design can be improved (it can), but whether a highway interchange on this scale should be built.

Comment by AWalkerInTheCity

Mon, 30 Apr 2012 14:08:30 EDT

to some extent the chicken and egg thing is legit, though. And to some extent its about time horizons and time valu of money. When an area is built out, you arent going to change it from autocentric to walkable without massive redevelopment. Even in a place like RBC, that took over two decades. And RBC was relatively walkable in many ways to start with. Its not likely that the demand for walkable TOD, will be sufficient to transform not only huge areas in DC, but every inside the beltway suburb, and every suburb within one mile of the beltway on the outside, within say, the next 30 years. The payback on the intersection could be accomplished before that.

Now I don't know Greenbelt well, so maybe its attributes (metro station, historic center) COULD make it a better candidat for transformation. And its probably always worthwhile to look for low hanging walk/ped fruit. But the issue of a place being thoroughly unwalkable is not necessarily properly dismissed as simply being circular. Some places can be bootstrapped up - some (like Tysons, to some degree) are so valuable they justify massive public investment - and some places just won't be able to break out of their legacy built form in an economically efficient way.

Comment by rodgerthat

Mon, 30 Apr 2012 14:02:53 EDT

There's a lot of ridiculous and unfounded commentary here. In the beginning at 0:50, there is no sidewalk. The sidewalk wasn't removed to create the diverging diamond interchange. This would be a challenge for a pedestrian in any circumstance. At 01:07, the video doesn't portray the undulation in the sidewalk treatment. The yellow concrete pad has patterned 3D bubbles to alert vision-impaired pedestrians. Again, this would be the same conditions for a standard interchange. The commentator is also belittling the vision-impaired by calling street traffic noise "terrifying". That is very condescending. With "weeds on one side" and traffic on the other, the commentator is identifying that this, indeed, is a sidewalk.

At 02:00 the commentator is concerned about safety for pedestrians. There is a striped buffer zone for the turn lane and a pedestrian island refuge that's some 25 feet wide. The clear striping and concrete island serves as a delineator for anyone who wants to safely cross. The red decorative brick is to provide a CLEAR and DISTINCT refuge for pedestrians that contrast with the road. The fact that there are large jersey barriers to protect pedestrians in the median is completely undermined by the commentator's discussion on the lack of pedestrian safety. I am over 4 minutes into a 10 minute video, and nothing this guy is saying holds water. Everything is "terrifying" and the "insanity" of it all is too great for the commentator. He would do well in a padded cell; that would keep him safe from this world.

Comment by Dave Murphy

Mon, 30 Apr 2012 14:00:54 EDT

For the record, I moved to Laurel in 2003 because I wanted to be able to walk to amenities. These ignorant stereotypes about Prince George's County are really unnecessary.

Comment by oboe

Mon, 30 Apr 2012 13:58:11 EDT

No one moved to PG County because they wanted walkable neighborhoods.

Or to Rockville, or Silver Spring, or Arlington, or many other walkable neighborhoods. At least they didn't before the local governments made a commitment to TOD.

In a related note, it never fails to suprise when people make the circular argument "It's okay that it's a traffic sewer, because who would want to walk or bike anywhere in that area anyway? I mean, come on, it's a traffic sewer!"

Comment by Dave Murphy

Mon, 30 Apr 2012 13:56:57 EDT

Here's why I like this idea:

If the divergent diamond decreases the wait time to get on an exit without eating all the land a cloverleaf would, ostensibly they could reduce the number of lanes on Greenbelt Road. Does that make that area more walkable? Not really. But having been an "entry level resident" of Prince George's County for eight years, I can say that there is currently little need for a pedestrian friendly environment there. If it reduces the number of lanes on Greenbelt Road, that will help further accomplish walkability in the area where new development WILL be occurring.

Of course, there is no indication that these lanes will be removed. In a perfect world they'd just get rid of that whole mess and turn Kenilworth Avenue back into a regular suburban road with an at-grade intersection.

Comment by Paul C

Mon, 30 Apr 2012 13:54:35 EDT

I grew up in Hyattsville, in PG, and my neighborhood has always been walkable. My parents bought the house in the early 70s, and I could walk to school, church, playgrounds, sports fields, and the library.

Comment by Michael

Mon, 30 Apr 2012 13:30:23 EDT

I predict many deaths at what I will call "the stupidest intersection this side of Springfield, MO".

The only way to make the area walkable is deck over the whole thing. Good luck with that.

Comment by Ben Ross

Mon, 30 Apr 2012 13:23:33 EDT

Oops - that was "tight curb radius."

Comment by Gull

Mon, 30 Apr 2012 13:22:37 EDT

The thing seems to just operate like a cloverleaf, without needing as much space to engineer it. You still have traffic having to merge in and out in a short distance on the same side of the roadway. These things were created to reduce the amount of time spent sitting at lights trying to make left turns in a traditional diamond interchange. Considering this being a state project when it comes down to ultimate build because both Kenilworth and Greenbelt Roads are State Roads, the State will have the same standards of having to make any new construction pedestrian friendly. I'd suggest lobbying the state for a separate pedestrian bridge that parallels 193 and goes over all the interchanging mess of vehicles. It's not ideal visually, but would probably be safer on a piratical point.

Comment by Ben Ross

Mon, 30 Apr 2012 13:18:44 EDT

I'm with Bossi (and I think with Matt Johnson too). I don't think interchanges are appropriate anywhere on the Beltway, except with other interstates.

It's not just about pedestrians at the interchanges themselves. It's about transitioning drivers from a limited-access highway to an urban street. They need to come to a full stop, or nearly so (at a streetcorner with a traffic light, stop line, and right curb radius). That resets their instincts to drive slower and watch out for pedestrians and bikes.

That kind of redesign would also free up a lot of wasted land that SHA could sell off to pay for the rebuilding.

Comment by BO

Mon, 30 Apr 2012 13:16:05 EDT

How much different is this proposal, than, say, the interchange of Rockville Pike and Montrose? Smaller scale, bigger scale, ?

Rockville Pike @ Montrose is sort of a half-diamond, and is a big wasteland of cement but at least there is (on one side of the bridge) a pedestrian sidewalk and I feel it is a slight improvement for pedestrians over the old intersection.

Comment by Bossi

Mon, 30 Apr 2012 12:54:31 EDT

I don't think the DDI itself need be considered any more pedestrian unfriendly than most other interchange designs. I've seen a mix of DDI's which are horribly designed for peds, but I've also been through some which are better than cloverleafs, parclos, and many diamonds. In my opinion, the better target (which this article does cover, as well) is whether an interchange of any variety is what's most ideal for the location.

Comment by HogWash

Mon, 30 Apr 2012 12:54:08 EDT

There's nothing about Prince George's that makes it any different from anywhere else in this regard.

Thank goodness! I was sitting here wondering why in the heck someone would even call any county "entry level," esp one as large of PG.

Where would anyone walk to east of this interchange anyway? It's Greenbelt Park to the south of 193 and then a large hotel/business park to the north. This doesn't scream pedestrian traffic to me</>

Ditto. I just assumed there were plans underway to totally change the landscape or something. Certainly not an area where I walk...or even want to.

Comment by @SamuelMoore

Mon, 30 Apr 2012 12:39:59 EDT

I'm from Springfield, and have ridden the DDIs on both sides of town several times. I'm now a cyclist here in the District and will say, they work in very specific situations to move vehicles onto an interstate very efficiently.

Springfield is very very far from a walkable city, at least where the DDIs are, however the above interchange seems like a perfect candidate to try a DDI.

Springfield, and MODOT are fairly progressive with traffic circles, and trying new, innovative (at least in the States) approaches to moving people. I think this post unfairly criticizes DDIs because Springfield is not a walkable city, not the DDI itself.

Comment by PG worker

Mon, 30 Apr 2012 12:36:49 EDT

Not sure why this would even need a redesign at all. Where would anyone walk to east of this interchange anyway? It's Greenbelt Park to the south of 193 and then a large hotel/business park to the north. This doesn't scream pedestrian traffic to me... just a waste of money. Perhaps it's not perfect but it's good enough as is.

Comment by Cavan

Mon, 30 Apr 2012 12:11:18 EDT

"PG county is the "entry level" place for people who want to live out the fantasy of a single family home with a yard and a garage where they can drive to the supermarket without having to spend a lot of money."

Just a simple change and you'd be onto something...

"PG county is the "entry level" place for people who want to live out the fantasy of a walkable urban place with beautiful public spaces and convenient access to transit without having to spend a lot of money."

For the record, I don't think that Prince George's is or should be an "entry level" place for 'people.' People move around for a variety of reasons. I just changed your statement to highlight how backward-looking it is.

However, rents per square foot (both commercial and residential) in walkable urban places have been higher than in car-dependent places for five years now. That implies more demand than supply. Why wouldn't the market also demand such real estate in and around Greenbelt in Prince George's County? There's nothing about Prince George's that makes it any different from anywhere else in this regard.

JustMe, that model I'm supporting is compatible with Prince George's future.

Comment by Common_Sense

Mon, 30 Apr 2012 12:03:25 EDT

Where do these alleged "engineers" get these foolish ideas? If they're being taught these concepts on a university level, perhaps it's time to examine some credentials.

Comment by JustMe

Mon, 30 Apr 2012 11:51:29 EDT

Put the automobile corridors on a diet, plain and simple. That area is too valuabe to be a traffic sewer in perpetuity.

Meh. No one moved to PG County because they wanted walkable neighborhoods. PG county is the "entry level" place for people who want to live out the fantasy of a single family home with a yard and a garage where they can drive to the supermarket without having to spend a lot of money.

The whole model you're supporting just isn't compatible with PG county's history and culture.

Comment by Cavan

Mon, 30 Apr 2012 11:48:41 EDT

David, you plan for the urban environment of your future, not accomodate past failures.

Or, perhaps the phrase, "If all you plan for is cars and traffic, all you'll ever get is cars and traffic. If you plan for people and places, you'll get people and places," is apt.

Put the automobile corridors on a diet, plain and simple. That area is too valuabe to be a traffic sewer in perpetuity.

Comment by Jack Love

Mon, 30 Apr 2012 11:44:11 EDT

At least it's not a diverging windmill.

Comment by David

Mon, 30 Apr 2012 11:12:49 EDT

If "the goal from the start were to make a space friendly to people walking and biking" then how many pedestrians would realistically utilize this area vs. drivers in the most ideal scenario? Maybe 1 ped: 10,000 drivers?

I share your distrust of diverging diamonds, but I also don't know how realistic it is for the an area where four major automobile corridors converge to become a vibrant, walkable, mixed-use neighborhood on all sides. There are multiple major barriers to pedestrian/bicycle movement there. Seems like the vast majority of the ped focus is going to be to the north and west of this interchange.