Traffic and Algorithms in Seattle
Bill Beaty, the amateur “traffic waves” scientist described in Traffic, writes in to describe his early experiences with Seattle’s new Active Traffic Management System — the “dynamic” system of varying speeds, imported from Europe, which is meant to ameliorate the impact of drivers driving into vast stop-and-go traffic (with the ensuing shockwaves).
Beaty was curious to note that the first part of the project is happening on the very section of I-5 where he first began developing his one-man crusade for traffic harmonization. Here’s how he describes his new commute, which seems to have some of the disequilibrium that new schemes bring:
In the first week it created very strange patterns: huge I-5 jams on
Sunday (when Sunday I-5 northbound has always been empty.) They now seem
to be tweaking their algorithm. Or perhaps drivers are no longer freaking
out. Patterns are still odd, but keep changing over many days.
From what I can see, they’re trying to limit the inflow to the daily
northbound jam at I-5 and I-90 interchange. The result is a large
slowdown far south of the city, with an empty region right at the location
of the daily jam. Very odd to encounter a major slowdown near my own home,
where there never was congestion before …but then at the usual location
of the giant I-5 snarl, the traffic flows free at 50mph. Presumably there
no longer exists any continuously-growing daily jam. Merging at city
exits has suddenly become easy. Probably the old jam has been converted
into shockwaves moving slowly backwards, rather than the previously huge
region of 20mph driving.
Another ATMS section is on I-520 …which is right where I first saw the
string of headlights that inspired my first online article. Bizarre
coincidences. Or maybe the bigwigs in the Seattle traffic control
community have all been reading my site? 
Any other Seattle-area readers/engineers care to share their experience?
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This entry was posted on Thursday, September 16th, 2010 at 2:42 pm and is filed under Cities, Commuting, Congestion, Traffic Gadgets, Traffic Wonkery. 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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September 16th, 2010 at 3:17 pm
I dunno, I lived in Seattle for 10 years, and worked in Redmond (on the other side of the SR-520 (It’s not remotely an I). If you ask anyone in the area who deals with Seattle traffic as a commuter where you need this kind of measure, they’d pick I-5 through downtown, and SR-520 from around the I-405 interchange to the floating bridge. As someone who grew up driving in NJ/NY traffic, those two stretches of road drove me batty for 10 years in a way nothing here ever has.
I have to admit I am curious what things will be like the next time I get back and have to drive that…
September 30th, 2010 at 1:12 pm
Interesting stuff — but I drive NB Interstate 5 frequently, and for years there have ALWAYS been mid-day slowdowns there on Sunday, both before and after ATM.
Traffic is sometimes slightly faster with the ATMs, but nowhere near the 40 mph on the signs. If we actually could go 40 mph through there, it would be cause for a festival.
Cheers, Mike Lindblom, Seattle Times transportation writer