Post #408: Toward a cost per car-trip avoided and cost per traffic-minute avoided.

Posted on October 6, 2019

Any post that starts with “Toward” isn’t going to get you to your destination.  So you are forewarned:  This is just the first of two posts.

Based on everything I’ve seen so far, it’s difficult and expensive to get cars off of Maple Avenue.  That’s really the genesis of this post.  If you don’t believe that, you could start with Post #331, no magic bullets for Maple Avenue traffic.  You could skim my various analyses of the Town’s recent traffic study (search “multimodal”).  Read my idea about behavioral modification to keep cars off the road.  Maybe toss in analysis of Capital Bikeshare, and end with analysis of microtransit.  See how hard it will be to use rental electric scooters effectively in Vienna.  Or you could just re-read the first sentence of this paragraph and say, yeah, sounds about right.

I’m using this post to organize my thinking before the Town Council’s next round of discussions about Maple Avenue.  But this ended up being too long, so I’m splitting it into two posts.

The point of this first post is that, ideally, the Town should come up with a way fully to offset the additional traffic that Maple Avenue redevelopment will cause.  That should be part of the overall MAC plan.  My next post will belabor that by talking about putting all the options into a single “cost effectiveness” framework. 

A simple illustration of the problem and the key question.

Let me start with an illustration of the key issue of MAC zoning and traffic.  And then try to lay out a systematic analysis.

Above you see an aerial view of the Giant Food shopping center parking lot.  Maple Avenue is at the top, and the shops are at the bottom.  This lot has almost exactly 600 parking spaces.

Now imagine parking 800 cars on this lot.  Not only would every space be filled, but there would be cars parked up and down every aisle.  Got the picture?  Cram this lot full of cars.

Now image emptying out that entire parking lot, mostly onto Maple, during the morning rush hour.

If this property is developed, under MAC, at the same density as 444 Maple West, that’s pretty much what you are going to get.  If built at that density, the residents would have about 800 cars.*  Most adults work outside the home.  And the overwhelming majority of Vienna residents drive to work.

*  The existing 444 Maple West ended up at 151 apartments and (I believe) roughly 1.4 residential parking places per apartment.  The Giant Food property is not quite four times as large.  That yields an estimate of (151 x 4 x 1.4 =) ~850 spaces.

I just want to use this to make a few key points.  First, people who live directly on Maple will have little choice but to drive on Maple.  Second, because this is a new use of Maple — as housing — all that new traffic is going to want to be on Maple during rush hour.  The new traffic will be perfectly synchronized with the worst periods of the existing traffic.  Finally, MAC can generate new “point sources” of traffic that are going to be difficult, if not impossible, for the existing lights to handle.  Allowing those new residents to enter Maple during rush hour is going to require longer red lights, on Maple, during rush hour.  It’s not even clear that there’s enough space, on Branch and Glyndon, to allow all those cars to queue up in an orderly fashion in order to get onto Maple.

Contrast that with Maple as a retail/commercial district.  I don’t know anyone who gets in their car and drives on Maple during rush hour solely to (e.g.) get the grocery shopping done, get a haircut, and so on.  Unless you are already driving on Maple (e.g., coming home from work), most people have the good sense to do their business at times other than rush hour.  The net effect is that traffic generated solely by the retail uses of Maple “shares the road” with the commuting use of Maple.

To sum this up:  By converting Maple Avenue to medium/high density housing, the impact on traffic is complex.  It’s not merely the number of additional vehicles that will use Maple.  In addition, it’s that a) practically speaking, most will have no choice but to use Maple, b) they will want to use Maple during rush hour, and c) they can be concentrated at streets and lights that currently handle nothing close to that amount of traffic.

That’s what we’re buying into, in the long run, by converting Maple to high-density housing.  What’s the Town going to do about that?  Anything?

What’s the Town going to do?  Well, under the original development of MAC, the Town’s answer was to stick its head in the sand.  Literally directed the contractors developing the MAC statute to ignore traffic as an issue.

Now, thanks to many people yelling about this issue, there is some hope that the Town will at least acknowledge it.  Might even do something meaningful about it.  I don’t even require them to repent of their prior position.  I just want them to wake up and realize this needs to be addressed.

A subtle but important point

We’ve always had traffic on Maple.  So what’s new?  Why should the Town care now?

In the past, the Town could plausibly regard Maple Avenue traffic the same way you might regard a particularly bad rainstorm.  The Town wasn’t responsible for the traffic.  It didn’t cause that traffic to happen.  And, in fact, there’s more-or-less nothing the Town could do to prevent that traffic from using Maple.  In no sense was the traffic on 123 the Town’s fault.  The Town did what it reasonably could to make our little stretch of Route 123 function.  And that was a valid and and logical way to view it.

You will still occasionally hear Town Council members continue to hold this position.  But it’s no longer a valid or logical position.  Sure, the Town is not responsible for commuters driving through Vienna to get to and from work.  But the Town is responsible for the additional traffic caused by MAC development.  By changing the zoning, and approving the buildings, the Town is directly responsible for the additional traffic caused by these changes.

If that additional traffic that the Town is creating were inconsequential, there would be nothing that needed discussion.  If it were going to amount to a few more raindrops within the hurricane of normal Maple Avenue traffic, then so be it.  The Town would have every right to keep its head in the sand.

But it’s pretty clear at this point that the additional traffic will be consequential.  The Town should have done the studies to determine this from the start.  It didn’t, and that’s water over the dam.  But now, everything from my illustration above, to extrapolating from the existing projects, to a simple back-of-the-envelope, to the Town’s own (flawed) traffic study all seem to be saying the same thing.  Yes, all this new housing on Maple is going to generate a meaningful  amount of additional traffic.  It’s not just a few more raindrops in the storm.

And as a logical consequence, the Town can no longer get away with singing “que será, será” whenever the issue of Maple Avenue traffic comes up.  For the bulk of it, sure.  For the additional traffic that’s a consequence of the Town’s zoning changes, nope.  That doesn’t fly any more.  We’re smarter than that now.  I hope.

Reiterating my proposal for changing MAC

See Post #322.

  1. Three story buildings.
  2. True open space requirements.
  3. Concrete, quantifiable changes to offset increased traffic.

And so this entire post, up to now, was to get you to see how I think point #3 above lies within the whole discussion of modifying MAC zoning.  Sure, these big new buildings have benefits in terms of tax revenues, housing choices, and blah blah blah.  But they come with a fairly substantial cost, not just to the neighborhoods directly adjacent, but to the Town as a whole.  And for most of Vienna citizens — those who don’t live directly adjacent to Maple — that cost can be summed up mainly by one word:  Traffic.  

This is not to disparage the other impact that Vienna population growth will bring, which is further stress on already-crowded Vienna schools.  I have already outlined what I think the Town ought to be doing about that (Post #327, Point 7).  Even though we don’t run the schools, I don’t see anything wrong with the Town advocating with the County on behalf of our citizens.  (And as a final thought, I would not dismiss the impact this will have on other public facilities, such as the already-crowded ball fields and other parks in Vienna.  But I’d say that traffic and schools are the top issues when it comes to fallout from MAC.)

Here’s what the Town named its ongoing Maple Avenue study:

Joint Maple Avenue Corridor Multimodal Transportation and Land Use Study“.

Here’s what I think it should have been titled:

“New Initiatives to Achieve Zero Net Additional Traffic From Maple Avenue Redevelopment.”

That study is what would address Point #3 above.  It would show you the Town’s plan for offsetting the additional traffic caused by MAC development.  That is, as Maple redevelopment adds cars, under this proposal, the Town would find way to keep an equal number of other cars off Maple.  Or as close as they could get.  To me, that’s the whole point of the study.

If the Town could write such a study — realistically, not just a bunch of gimmicks — then I think that a good part of the Town-wide objection to MAC would disappear.  If you don’t literally live next to Maple, and you aren’t particularly worried about school redistricting, what do you care if a bunch of people choose to live on Maple?  As long as they don’t get in your way as you’re trying to get around town.

This is, admittedly, an extreme and probably inefficient stand.  Net zero additional traffic.  It’s far from clear that this is possible, and it’s probably not cost-effective.  But given the Town’s propensity to turn a blind eye to this, maybe it serves as a useful line in the sand.  Something you can turn to the Town and say, OK, that’s one view of what the goal is.  Now, what, exactly, is the Town’s goal in all of this?

Traffic aside, one could reasonably might still object to (e.g.) the look of a redeveloped Maple.  I don’t like lot-covering buildings 20′ off the road.  And most people really don’t much like using parking garages.   And there’s still the issue of schools and parks.  But my guess is, if you didn’t make their day-to-day lives any worse with additional traffic, most people in Vienna would just shrug this off and move on.


I suspect I’m way past the TLDR point on this post, for most readers, and I’m nowhere near done.  What I want to do next is suggest the framework for transforming the Town’s study (“Joint Maple …”) into my study (“New Initiatives …).  That’s going to have to be my next post.