A traffic service that answers “which way should I go?”


Which way should I go?

Most traffic reports (on the radio or in text message alerts) are fairly useless. Like weather reports they contain lots of irrelevant information that could be eliminated with just a bit of extra context. In fact, most of the information they deliver is completely irrelevant to you as an individual located in one spot and hoping to get to another spot. Furthermore they aren’t actionable - telling me the traffic is slow on SR-520 and on I-90 isn’t interesting unless you can tell me which is the best way to go given where I am now and where I want to be.

So this weekend I added a new feature to the home automation that uses the WSDOT’s excellent traffic feed API to calculate a traffic report just for me. Recently I’ve started driving from the north end of Bellevue to the south end of Sammamish during rush hour. There are two very different paths I can take: SR-520 or I-405 to I-90. If either route has a problem I should take the other. So now I get an XMPP (chat) message from 4PM to 6PM whenever the optimal path changes from one route to the other. It’s the absolute minimum information I need and it’s 100% actionable.

For the moment the calculation is fairly simple, I simply maintain a list of the FlowDataID values along each route and then calculate a total ‘slowness’ factor based on the sum of those segments. If one way is much better than the other it generates an alert. If it goes back to being roughly equal the alert is cleared.

Since the calculation is purely relative (route A vs route B) it’s also fairly immune to day-of-week / school-holidays and other factors that have a significant impact on traffic but no impact on the only actionable decision I need to consider.

One other interesting point from the graph is just how spiked the traffic is on SR-520 compared to I-90.

Tue Oct 18 2011 06:22:28 GMT-0700 (Pacific Daylight Time)

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