Prediction: WB Highway 40 will not jam at I-170

As mentioned in the introductory post for this blog, I will have regular posts that predict how traffic will flow after the Highway 40 construction is complete. Not that I have any credentials to do such predictions, but, honestly, it’s fun, and if I’m wrong, well people will have forgotten about it by December 31, 2009 anyway.

I thought I’d start with an easy prediction: Westbound 40 will flow more smoothly at I-170 and not jam as regularly as it did pre-construction. Let’s at least hope so! If we’re spending $535 million to improve the highway, one might expect to it flow a little more smoothly.

In order to back up this prediction with some analysis, let’s look at what was causing the regular westbound 40 jams pre-construction. The key is to look at where the jam clears up, not where traffic begins to slow down. For westbound 40 during the evening rush, the slowdown might start as far back as the Science Center, but it would always open briefly right between Hanley and I-170 before another (sometimes brief) slowdown just west of Brentwood. So, we need to focus on the Hanely/I-170/Brentwood area.

The map above shows the key chokepoints on Highway 40 pre-construction. Traffic from Hanley road onto westbound 40 was forced to merge quickly and criss-cross with traffic that was destined for northbound I-170. All of this lane changing in a short time slows down traffic, and the backup just propagated further back as the evening rush volume increased. Once all the cars had completed their lane changes, traffic would open back up again just past these two chokepoints, until traffic from southbound I-170 and Brentwood tried to squeeze into the three lanes of already-near-capacity traffic on westbound 40. This caused the final chokepoint in the daily commuter’s trek along westbound 40.

The design for the new Highway 40 eliminates these chokepoints, which will lead to a much smoother flow of traffic through the I-170 interchange. The video below, courtesy of Gateway Constructors, shows how westbound 40 will look after the construction.

Video from http://thenewi64.org courtesy Gateway Constructors (Problems viewing? View directly and fast-forward to the one minute mark.)

To view the designs up close, take a look at the Brentwood/Hanley/I-170 plans from thenewi64.org. If you zoom in, you will notice two key points:

  • No direct merges from Hanley to westbound 40 — this eliminates the first two chokepoints, since Hanley traffic won’t merge until after traffic bound for I-170 has already exited. (A future prediction will look at what this means for Hanley and Brentwood)
  • Additional lanes to support merging westbound traffic — Plans had always talked about an extra lane west of I-170, but in fact there will be two extra lanes between Brentwood and McKnight, giving plenty of space to absorb traffic joining westbound 40 from I-170, Brentwood, and Hanley.

Interestingly, construction crews have already eliminated the Hanley access points to westbound 40. If it weren’t for the large lane shift at I-170, I suspect you’d already see fewer backups on westbound 40, due to the elimination of those short merges and criss-crosses.

Overall, this is a very positive new design that should make for more pleasant evening commutes at this complicated interchange.

This entry was posted on Monday, June 25th, 2007 at 10:12 pm and is filed under Brentwood, Hanley, I-170, Predictions. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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