Food trucks are a bit of a silver bullet for urbanists, because they add to street activity without triggering many of the externalities of new construction. In a survey of food truck policy in the Pacific Northwest published just about everywhere, Eric Hess says Seattle has not achieved food-truck nirvana:

Have the rule changes panned out? Not yet. Since July, the city issued seven new permits for food trucks—defined in Seattle as self-powered vehicles with kitchens onboard—to vend from public streets, and six permits for food carts—think hot dog vendors or push carts—to vend from sidewalk spaces. The numbers don’t signal an explosion of street food. In fact, the number of food cart permits actually dropped a bit since the new regulations took effect… In Seattle, street food is also on the rise, but largely missing from dense, walkable neighborhoods where it has much to offer. The city lifted many archaic rules, but there’s more to be done.

Erica Barnett follows up with a little more, including this analysis from Sally Clark:

Basically, [Clark] said, she has no idea. One theory, though, is that scarce street parking makes it more profitable for parking-lot owners to use them for parking than lease them to food trucks. “The thing is, actually think seven or eight is a good number for people who want to serve in the parking area or in the sidewalk,” she adds. “It’s just not all that well tested in Seattle yet.”

In the end, thought, I think Yglesias asks the right question: is this really a failure of the rules?