Is this sidewalk placement unique?

[1995hoo]

I've passed this spot many times but never paid a lot of attention to it until last Friday. See Bing Maps link below (I've used Bing due to the antipathy Google Maps has generated). It shows Virginia State Route 7 (King Street) in the City of Alexandria where it crosses over Interstate 395. Route 7 is the wide road running diagonally across the image. You'll need to pan left to view the whole scene.

What I found interesting is the sidewalk on Route 7. Notice it's in the median. There's a crosswalk on the eastbound side of Route 7 at the bottom of the image (no corresponding crosswalk on the westbound side because there's no pedestrian walkway on that side) allowing pedestrians to access the median sidewalk. Pedestrians are then to cross I-395 on the median of Route 7 and follow the sidewalk to the first signalized intersection on the north/west side of I-395, at which point crosswalks connect to sidewalks on either side. I can't say I've ever noticed any pedestrian actually using this median-located sidewalk, though.

I found myself wondering if this is a unique configuration because I don't ever remember seeing anything similar anywhere else. It seems like a good idea in principle because it eliminates the need for crosswalks on the highway on- and off-ramps. I can think of other interchanges around here that use crosswalks on the ramps–see the Google Maps link below for an image of one such (I used Google for that because Bing had an outdated image). I've never thought that's a particularly desirable configuration.

Anyone know of other places configured like this?

Sidewalk in question: http://binged.it/1viLQva

Sample of crosswalks on ramps: http://goo.gl/maps/yS9sE

[Big John]

Sidewalks are put in the median in DDIs too.  But it looks like there was not enough ROW to put it on the side of the road there.  May have been other factors why the median was not narrowed there.

[jeffandnicole]

Here's a sidewalk that appears to have remained from this I-295 interchange's original configuration with US 130: http://goo.gl/maps/sLRJb

The sidewalk is in the inside of the ramp.  It's old and right next to the roadway, so it makes it hard to see.  If you zoom out to the south, the sidewalk ends opposite of the small slip ramps.  To the north, the sidewalk ends about 50 feet from the road.

[kurumi]

There's a sidewalk in the median of El Monte Road at I-280 in Los Altos Hills, CA for the same reason: to separate pedestrians from cloverleaf ramps.

http://goo.gl/maps/VZxkm

[2Co5_14]

That reminds me of a funny situation I heard about.  Some citizens were complaining about why GDOT was installing a sidewalk in the median of GA-400, a major freeway in metro Atlanta.  It turns out that the "sidewalk" was actually just the concrete footing for the median cable barrier that had yet to be installed!

[froggie]

I've never thought that's a particularly desirable configuration.

It's not.  The median is not a preferred location for sidewalk placement, which is one of the complaints I've seen about the standard DDI design.

[Duke87]

The DDI design is clearly idealized for vehicular traffic flow with pedestrians as an afterthought. The sidewalk has to be moved to the median in order to keep the crosswalks at signalized points. The two left turn movements onto the freeway are free-flow and unsignalized with a DDI, so you can't have pedestrians crossing there without adding extra signalization and defeating the purpose.


On the other hand, while walking in the median seems unpleasant on account of being an isolated location, is it really more isolated than a sidewalk on the side of a freeway underpass? I'd guess that it really isn't but then I've never walked through a DDI so I can't really comment.

[1995hoo]

I've never thought that's a particularly desirable configuration.

It's not.  The median is not a preferred location for sidewalk placement, which is one of the complaints I've seen about the standard DDI design.

I was referring to crosswalks traversing on- and off-ramps when I made that comment, although I certainly see and agree with the validity of your comment about median sidewalks.

[vdeane]

The DDI design is clearly idealized for vehicular traffic flow with pedestrians as an afterthought. The sidewalk has to be moved to the median in order to keep the crosswalks at signalized points. The two left turn movements onto the freeway are free-flow and unsignalized with a DDI, so you can't have pedestrians crossing there without adding extra signalization and defeating the purpose.


On the other hand, while walking in the median seems unpleasant on account of being an isolated location, is it really more isolated than a sidewalk on the side of a freeway underpass? I'd guess that it really isn't but then I've never walked through a DDI so I can't really comment.

The one in Rochester has the sidewalks on the outside with the understanding that vehicles are supposed to yield to pedestrians and that pedestrians should look before crossing.  Of course, pedestrian volume isn't high here, and the median is just a jersey barrier dropped in the center.
https://goo.gl/maps/rsVbZ

[TEG24601]

This actually makes sense, to get pedestrians away from the ramps.

[froggie]

It makes sense from a driver perspective, but it doesn't from a pedestrian perspective.  For two big reasons:

- First, instead of being hemmed in by traffic on one side, pedestrians are now hemmed in on BOTH sides.  This can be a huge psychological barrier, plus a potential double-whammy from road grit/debris that gets kicked up by car tires and truck exhaust.

- Second, instead of crossing the lower-volume ramp traffic, pedestrians must now cross the higher-volume through-street traffic.  Whether there's a signal or not is inmaterial here...it's still a higher exposure rate, using a #-of-cars times #-of-peds formula.

I don't see why they can't keep sidewalks on each side of the roadway through a DDI, instead of funneling bikes/peds through the median.  The off-ramp terminals can easily be configured for signals...some recent DDIs are already configured like this.  The primary conflict issue with peds would be the on-ramps, though the nature of the DDI signals ensures that there will be gaps in the left-turn on-ramp traffic.  And proper right-turn-lane design (as opposed to a free-right) can mitigate some of the pedestrian issues with right-turn on-ramp traffic.

I'm thinking mostly of urban-style installations here (like what I proposed in New Orleans several months ago in the Fictional threads), though it'd also work anywhere where there are pedestrian safety issues at a given interchange.

[johndoe]

The one in Rochester ...
https://goo.gl/maps/rsVbZ

Not to threadjack, but I'm always confused when their are more lanes on the crosstreet at the bridge than at the approaches.  The southbound direction looks like it could have 3 lanes under the bridge.  To the north there is plenty of space in that median to build a dedicated southbound left turn lane.  The bridge width is the expensive part, why not use all the width you have?  Any advantage to this? 

[johndoe]

It makes sense from a driver perspective, but it doesn't from a pedestrian perspective.  For two big reasons:

- First, instead of being hemmed in by traffic on one side, pedestrians are now hemmed in on BOTH sides.  This can be a huge psychological barrier, plus a potential double-whammy from road grit/debris that gets kicked up by car tires and truck exhaust.

- Second, instead of crossing the lower-volume ramp traffic, pedestrians must now cross the higher-volume through-street traffic.  Whether there's a signal or not is inmaterial here...it's still a higher exposure rate, using a #-of-cars times #-of-peds formula.

I don't see why they can't keep sidewalks on each side of the roadway through a DDI, instead of funneling bikes/peds through the median.  The off-ramp terminals can easily be configured for signals...some recent DDIs are already configured like this.  The primary conflict issue with peds would be the on-ramps, though the nature of the DDI signals ensures that there will be gaps in the left-turn on-ramp traffic.  And proper right-turn-lane design (as opposed to a free-right) can mitigate some of the pedestrian issues with right-turn on-ramp traffic.

I'm going to respectfully disagree with just about everything you said 

1.  As far as it being "hemmed in", compare it to a normal interchange with a wall on one side and a curb and gutter on the other.  Is this any better?  Any time a ped is crossing under/over a bridge the width is likely cramped.  Every DCD (sorry, I still think this name makes more sense than DDI  ) I've seen with peds in the middle has jersey barrier protection on both sides.  This barrier keeps the ped path just as, if not more, clean of debris/exhaust as any other path you'll find.  It's a bit different to see traffic on both sides of you, I have always felt safe walking down the center in the few I've walked.  The only way to get to that position is crossing the signalized crossover, which pedestrians feel more comfortable with since they're crossing with vehicles making the same movement.  Opposing vehicles are expecting to stop for the signal.  On the other hand, vehicles aren't looking for peds at the free lefts onto ramps.

2.  The ramp doesn't necessarily have a lower volume than the cross street, I've modeled areas where the ramp is higher.  Also, whether or not there is a signalized ramp terminal does matter... 

on-ramps... As previously mentioned vehicles are not expecting to have to stop at the free left.  Without this being signalized the likelihood of a pedestrian conflict is increased.  Where the DCD is below the bridge you're almost guaranteed to have sight distance problems for vehicles due to the bridge columns.  They won't see the peds who want to cross.

off-ramps... In some cases it's more efficient for vehicular traffic if the ramps are unsignalized.  (Yielding left and yielding right)  In this case, doesn't it make more sense to cross the peds where there is a signal (the crossover of the DCD) than the yielding left of the ramp?  Adding signals where they're not needed is going to increase project costs, vehicular delay, and crashes.

The other part is cost; bridges are expensive.  Generally less bridge area is required for one center walkway as opposed to two outside paths.

I'm not saying two outer walkways are bad; I'm just saying there are good reasons to put peds in the middle.

[Tom958]

It makes sense from a driver perspective, but...

I'm going to respectfully disagree with just about everything you said 

It would be interesting to see what experience teaches us about this. Now, are there enough DDI's/DCD's with sidewalks on the sides to provide a statistically meaningful comparison? And, if so, how would one go about measuring the extent to which pedestrians are so intimidated by how the walk is routed that they avoid it altogether?