Lately, I've seen speed bumps with trenches dug through them. I approve of this—I can align my tires with the cutouts and not slow down as much—but I can't help thinking my convenience isn't the reason. What's the deal? —Trench Foot
We'll deal with your scofflaw tendencies in a moment, Foot. First, journey with me to a magical land of never-ending sunshine, where speed bumps may soon become a thing of the past.
Around the year 2000, the United Kingdom (I lied about the sunshine) started incentivizing people to buy diesel cars, which emit less CO2 than those that run on regular gasoline. Unfortunately, diesels emit more nitrogen dioxide (NO2) and soot than their petrol-powered brethren—emissions that are worse when the car is accelerating.
Thus, some U.K. environmentalists have suggested that speed bumps—which cause frequent slowing down and speeding up—should be eliminated. Of course, other environmentalists have called this plan "daft," but we can dream.
As for those channels you're seeing in Portland speed bumps, they're spaced such that ambulances, fire trucks and the like can drive over them at speed without having to slow down.
One channel runs directly down the road's center line, so regular drivers can't use them—unless they, you know, steer slightly to the left, so as to put their left tires in the center channel.
Also, you need a wide vehicle, like a truck, to make full use of the channels. Lucky for us, there's no correlation between big trucks and people who drive like assholes.
I should stress that this maneuver is both dangerous and totally illegal—you're partially steering into oncoming traffic—but BikePortland.org has already published photos of people doing it.
Still, the new bumps should keep reasonably law-abiding motorists from speeding. An incorrigible few may try to take advantage, but at least it'll keep them off the sidewalk.