Study area of WSDOT's I-5 - Fort Lewis/McChord Transportation Analysis
This is the first post in a series about the Tacoma to Olympia Corridor. This post is all about I-5 and focused mainly on where it matters most which is through the small sliver of the Joint Base Lewis-McChord area where it cuts through. The base is a city in itself and is expected to grow significantly in the coming years. In 2001 the population in Fort Lewis was 18,000 people, and up to 30,000 more people (pdf) are projected to move near the base in the future.
I-5 functions as the main artery through the base and is the main artery for traffic through Western Washington as well. The pressure of traffic from the base combined with through traffic causes some serious congestion. As reported in WSDOT's 2008 Annual Traffic Report (pdf), a typical weekday would see 119,000 vehicles traveling on I-5 by DuPont and on 129,000 on a typical Friday. Over an average week, over 285,000 vehicles (pdf) accessed the Fort Lewis base.
If that weren't enough, this is all about to be exacerbated by a highway maintenance project this summer. The TNT had a good writeup on the project on Monday. This WSDOT project will replace a lot of the concrete panels along I-5 which will at times require closing 3 lanes at once. Backups can be expected to be up to 10-15 miles long.
WSDOT is also analyzing future operating configurations along I-5 in a study funded mostly by the Department of Defense. As expected, the study is a typical corridor analysis spending a great deal of effort in improving vehicle operations. There is mention of transit, but in a hypocritical way (more on that in a later post). In the latest round of analysis, the alternatives were summed up in the following table:
Scenario 1 includes modest interchange improvements. In the #2 scenarios interchange improvements are added. Finally, in the #3 scenarios a new General Purpose Lane is added that between Thorne Lk Rd and Mounts Rd in addition to the #2 improvements. As expected, the #3 scenarios score very high since vehicle mobility was weighted four times more important than environment or benefit/cost analysis. The interchanges proposed vary at each existing interchange and sometimes include SPUIs and even DDIs.
For those wondering what a SPUI is, it's a Single Point Urban Interchange. Tacoma has one at I-705 and 21st. However, a DDI is a completely new concept for Washington State. DDI is short for Diverging Diamond Interchange which means that traffic flows briefly on the other side of the road so traffic can freely enter on-ramps or exit off the freeway onto the road without having to wait at a red light for a left turn. The Missouri DOT has a Flickr set of their DDI which was the first built in North America. Here is one of those pictures: