By now you’ve probably heard about the idea to turn the Downtown Houston freeway loop into a giant traffic circle.
It’s a useful concept, in that it clears the idea space for other radical ideas. I was once on a Value Engineering committee where we were discussing storm drainage design alternatives. I proposed “Amish children with buckets.” Now, there was approximately a 0.0% chance of Amish children being selected. But it made everybody laugh, and it made any other crazy ideas seem just a little bit less crazy. In politics they call this the Overton window.
So now we turn to what might be done with the downtown Houston freeway network. And I think it’s useful, before we get into traffic counts, before we send out origin-destination surveys, before the consultants show up with detailed microsimulations, to just take a step back and look at the big picture.
Coming in on 59, after the Spur peels off you have six lanes. There’s a short weave where traffic comes on from San Jacinto and heads off onto 288, and then you’re once again at six.
Coming in on 288, after the ramps to 59 south peel off you have eight lanes. It gets sort of complicated because the northbound freeway widens out in anticipation of as-yet-unbuilt express lanes, but in the southbound direction it’s a pretty simple setup of two lanes from 59 and two lanes from the C-D from 45. So oversimplify and call it eight lanes for both directions.
Coming in on 45, you lose the C-D to “Downtown Destinations” and pick up a lane from Spur 5, which leaves you with an eight lane cross section going over the Columbia Tap. (I’m not counting the C-D lanes since they don’t interface with the downtown freeway loop).
That’s twenty-two lanes total. How many lanes are available downtown? The Pierce Elevated has six. And a cross-section of 59 at the GRB has eight. Add ’em up and you get fourteen. 22 into 14. 11/7. This is why the Pierce comes to a standstill.
Of course, some traffic is headed from 59/288 to 45, and won’t enter the downtown freeway loop. Presently the ramp from the 59/288 C-D to 45 SB is one lane. So let’s subtract one lane each way from 45 and 59/288. You still have eighteen lanes into fourteen. 9/7. The approaches have 30% more capacity than the loop does. Since the downtown freeway loop already has pretty good geometry, any proposal which doesn’t address this imbalance probably isn’t worth considering.