A Tuesday without TNUA
Instead of riding the TNUA last night, I attended a DOT public information meeting where they presented design proposals for improving the intersection of an expressway and a major surface street. I commute through there regularly, several of our bike club routes traverse it, and it’s between a residential area and a MUP.
That alone made it important enough that I gave up going with the regular Tuesday night ride in order to attend.
But what really got me there is that they’re proposing a new type of intersection, called a Diverging Diamond Interchange, or DDI. (Google on it.) I was horrified by what I’d seen on the news, and went loaded for bear to fight for cyclists’ rights.
Three very amazing things happened instead.
First, the simulations they showed actually looked pretty darned good, from both motorists’ and cyclists’ views.
Second, when the question period opened, the very first question, and about half of those that followed, pertained to cyclists and peds. I never had to open my mouth. Other people asked the same questions I was going to, and the answers were all reasonable.
Third, afterwards, I went to talk with the engineers. Seeing my helmet and hi-viz, they said, “You’re just who we need!” Instead of me pushing to get on to a committee or something, they recruited me! Learning I was a club member as well as a commuter, they asked me to bring as many cyclists as I could round up to meet with them, view the simulations and comment.
In one engineer’s words, “None of us are cyclists. We know what looks good to us, but we don’t know what works best from your perspective. We need your help.”
Knock me over with a feather…
In any event, DDIs have been proposed several times before in the US, however none have yet been built. If built, this will be the first Diverging Diamond Interchange in the US. I’m looking forward to having input into what will certainly become a model for others. I meet with other cycling advocates next week, and we meet with the engineers during the week of March 3rd.
The original DDI is in France. It’s been running since the 70s. Of the material I’ve found on the web, this “techbrief” from the FHWA is closest to what was presented last night.
The design has evolved considerably since the French one, plus there’s a little more real estate available here. Also, while we have additional nearby intersections, they’re not that close. Finally at ours, the freeway is on the overpass, but that’s insignificant.
What they’ve done is lengthen the whole thing. Then with some extra width, the two sides swing apart further before they cross, so the crossings are closer to 90°.
The thing looks really, really weird at first, and quite dangerous. But as I sat looking at the simulations—both from a bird’s eye view and windshield view, I liked what I saw.
First, is the two-way signal phase reduced from three. This gets more traffic through in any given amount of time. Less traffic is a good thing as far as I’m concerned.
Second, although that section is posted for 40 MPH, 55 and 60 are more typical. The basic weirdness and criss-cross have a traffic-calming effect. I’m all for slower traffic off my left elbow.
Third, the criss-cross eliminates left turns crossing the path of oncoming traffic. There will be no more cars trying to shoot the gap then discovering I’m in it.
Fourth, in the criss-cross, all new traffic enters on the left leaving me protected on the right.
It looks like lane width and shoulder width will help within the criss-cross. My biggest concerns right now are the usual ones we have whenever a feeder lane breaks off to the right or joins from the right before and after the criss-cross.
Some drivers get confused, thinking I belong along the curb at all times, even when the curb is a right turn only (and in this case onto an Interstate highway) when I’m going straight ahead. To them, it appears like I’m riding in the middle of the road, when in fact, I’m in the right side of the rightmost lane traveling in my direction—exactly where I belong. Sure there’s a whole lane to my right. But that’s not where I’m going.
The engineers are talking about marked bike lanes there, but I haven’t seen the plans yet.
As for ped crossings, I’m not so sure. Peds will have four crossings instead of two, and three of those are uncontrolled “free-flow” lanes.
Anyway, for those keeping score, that’s why I missed TNUA. There were bigger fish to fry. And I still had a nice ride in the snowstorm.
February 14th, 2008 at 6:48 pm EST
yikes, it looks pretty scary from the picture, but I can’t even imagine how it works. I guess I’d actually have to experience it to appreciate the design.