The Express Lane Isn’t Faster
Reader Mike had sent along this great post from a California math teacher who analyzed supermarket checkout times (data, as pictured above, was provided by the supermarket manager). I’m slow to post this and it has now been around a lot, but this was catnip to me as I love these sort of operational/logistical/queue problems (and this relates a bit to the airport walkway problem), particularly when they seem to exhibit that classic “slower is faster/faster is slower” effect. Not to mention that “other lane is always moving faster” problem that plagues us in traffic is a very real issue in queuing as well (and is partially why some outfits use single lines).
Among the many interesting findings:
The express lane isn’t faster. The manager backed me up on this one. You attract more people holding fewer total items, but as the data shows above, when you add one person to the line, you’re adding 48 extra seconds to the line length (that’s “tender time” added to “other time”) without even considering the items in her cart. Meanwhile, an extra item only costs you an extra 2.8 seconds. Therefore, you’d rather add 17 more items to the line than one extra person! I can’t believe I’m dropping exclamation points in an essay on grocery shopping but that’s how this stuff makes me feel.
There’s ways this can be applied to traffic, but reader Mike was wondering about those express/local lanes on highways. I only know anecdotal stuff here, like stories of engineers changing the estimated times on both segments when they really want people to use one or the other. But this is a bit of a guessing game every time I approach the George Washington Bridge on I-80. I’ve been burned many times by the express lane — is it the very wording, which fools me into thinking it’s a better way to go than that inevitably cluttered and slower “local” lane? It of course depends on many variables, like the intended destination of traffic, etc.
Maybe there’s some geeky studies somewhere of tolling as well; exact change lanes versus others, etc.; though those are likely to be outmoded with EZ-Pass etc.
This entry was posted on Tuesday, September 22nd, 2009 at 9:36 am and is filed under 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.