Driving to Reduce Congestion

Nearly everybody has noticed that the roads are getting more and more congested.  There's a reason for this:  we quit building new roads during the 1970s, but we didn't quit making new cars or people driving them.  US population has grown about 50% (more than doubled where I live, near Puget Sound in Washington State), while very few new high capacity roads have been built (no new ones here since the 1960s, although a few have been widened a little).

Congestion is not just annoying.  It wastes fuel, it wastes time, and it causes accidents.  People drive more aggressively when they're frustrated.  I wonder how many people have died because their ambulance or fire truck was slowed by traffic.  We might solve these problems by building more roads, or by building alternatives like rail (or better alternatives like Personal Rapid Transit), but efforts to do this have been stymied by anti-tax crusaders.   (I'm of the opinion that if you don't want to pay for infrastructure, you should probably refrain from using it.  This means you, Tim Eyeman.)

Since it looks like we won't be getting better roads, we should probably try to modify our behavior to improve the capacity of the ones we have.  This can be boiled down to two simple rules:

• Don't block traffic, and
• Don't drive too close.

There are lots of ways we block traffic.  The most obvious is pacing.  By this I mean driving the same speed as the car next to you.  If you're driving the same speed as the car next to you, you should be in the same lane.  The left lanes are for passing.  Only.    If you're not passing, you should get out of the left lane.

Some may argue that if you're going the speed limit, then you shouldn't go any faster.  Ok then, if the right lane is going the speed limit too, you won't be hurt by joining them.  There's someone behind you who is trying to get by.  Even though he/she would be breaking the law, let them.  If they're determined to speed, you should want them to be as far from you as possible lest you get caught up in their accident.

It's already illegal to delay 5 or more cars in Washington.  (in California it's 3).  Driving in the left lane other than to pass is also illegal.  I think the cops should announce that they're going on a campaign to ticket aggressively for this and cite drivers who are pacing for both offenses.

Another way to block traffic is in right turn lanes.  At traffic lights, it's legal to turn right against the red after having stopped to check for cross traffic.  But if there's a car going straight in front of you, that's not possible.  Suppose 25% of the cars going your way would like to turn right.  If you let them go, you speed up travel time for them the full light cycle, and since they're not part of the crowd waiting for the light anymore, you've reduced the number of cars waiting for the light by 25%--speeding up travel for people going straight too.

For some reason Washington State traffic engineers don't like dedicated right turn lanes.  It seems to me that they're safer and more efficient (for example the free right occurs when pedestrians can't cross), yet there are a number of places they've actually been removed.

Just a reminder:  Don't pace.  Get out of the left lane if you're not going faster than the cars in the right lane.

One of the worst traffic offenses I can think of is using a smoothly flowing lane of traffic to bypass a long line of slow-moving cars, and then when you get to the front of the line, forcing your way in.  This slows the formerly smooth traffic to the speed of the blockage.   I call this "intentionally causing a traffic jam" and I think it should be ticketed as such, with the same consequences to your driving record as being found at fault in an injury accident.   (Most people who do this are assholes and know exactly what they're doing.   But it's possible you didn't realize this long line was waiting for your exit.  When you do realize, try to find a place to get in as soon as possible and wait your turn, but don't block traffic in your lane.  If it's not possible without slowing down your lane, go to the next exit.  This is often a good strategy anyway.  In all the cases where this happens regularly that I know about, the next exit is less than a mile farther along and it's a better route than waiting 20 minutes)

Did I mention that I think eliminating pacing is one of the best ways to improve the capacity of our roads that there is?

Now we get to tailgating.  Worldwide, highway engineers have found that when traffic gets denser than 1800 vehicles per hour per lane, the capacity of the road suddenly drops.  One traffic engineer I spoke with calls this phenomenon "falling off the cliff".  It varies a little due to factors like lane width, curvature, and weather, but basically, if highway volume is lower than the threshold, the little perturbations that occur are quickly damped by gaps in the traffic.  If traffic gets denser than the threshold, there aren't enough gaps and a little perturbation becomes a big stoppage and the capacity of the road goes to 500/hr or less.  1800 vehicles per hour works out to 2 seconds apart, which is (not coincidentally) just exactly what your drivers training instructor told you when you were learning to drive.   There's no point in driving closer than 2 seconds behind the car in front.  If you tailgate, you might be the one to cause the jam (or worse).  If demand for the road is higher than 1800/lane/hr, you aren't going to get where you're going at the speed limit anyway.

And one last thing:  don't pace.