One of the most reliable backups inside the Loop right now is the PM reverse-commute inbound on 59. In the early afternoon, when most of the Transtar map is green, the Shepherd-Spur segment is yellow. By the height of the rush, the queue extends at least to Buffalo Speedway. This happens for a number of reasons – but first, the fix.
Move the diverge point to Shepherd.
So add a couple miles of barrier and put the split at Shepherd. If you’ve driven this route once, you can see how it would immediately shave several minutes off the trip to Downtown/Midtown/Montrose. The Spur is never jammed in the reverse direction, so anything that effectively lengthens the Spur lengthens the distance of hassle-free 60mph cruising. But such a configuration would also help drivers continuing on 59. Here’s why.
Why does 59 back up?
In short, three tailbacks and a weave. 59 through Midtown consists of three lanes which split into three freeways, and backups on any of these are telegraphed through onto the mainlines. The splits:
(i) The two left lanes head to 45. While there is a predictable queue to get onto the Pierce Elevated, it rarely backs up onto 59.
(ii) The two right lanes head to the Eastex Freeway, continuing as 59. This is a more common location for congestion, as there are two lanes coming off 59 and two lanes coming off 288, which narrow to three past the GRB.
(iii) An auxiliary lane gets picked up from San Jacinto which peels off onto 288 after a few hundred feet. 288 South is often backed up, and any tailback from 288 will cause the weave from San Jac to break down, effectively taking out two lanes. This by itself is sufficient to back up 59 past Shepherd, even if both the Eastex and the ramps to 45 are relatively clear.
Even when all three destination freeways are running smoothly, the short weave from San Jac still causes a reduction in capacity that is available through Midtown.
How does moving the Spur diverge point westward help? Because the Spur merge acts as a repeater for the Midtown bottleneck. In a normal traffic bottleneck you have three zones. You have the bottleneck itself, you have a queueing section where traffic stacks up waiting to get through the bottleneck, and then you have a free flow section upstream of there.
As traffic backs up on 59 past the Spur, drivers are faced with a dilemma. Do I sit and queue here in the right three lanes, which aren’t moving? Or do I get over and zoom past until right before the split? Many, understandably, choose the latter. But what this does is create a new bottleneck at the point where the Spur diverges, because traffic is merging into the left lane and then trying to cross over to get to 288 or stay on 59.
Wouldn’t a Shepherd Spur Split just move the repeater point to Greenway? No, for two reasons. First, a lot of the time the backup from 288/59/45 will never make it to Shepherd. Cars will happily (or not) queue up in the right three barrier-separated lanes, and the end of the queue will be somewhere between Midtown and Shepherd. And when it does make it back there, it still won’t be as bad, because there are already auxiliary lanes between exits in Greenway.