A total of 166 ramp meters —- the lights that control entry onto freeways —- are expected to be in use on interstate on-ramps around Atlanta by 2009. Fifteen new ones were installed last month along I-285 between Northside Drive and Buford Highway. Drivers dislike ramp meters, says "Traffic" author Tom Vanderbilt. The AJC asked him whether they work. His response:

They do. In Minnesota, the Twin Cities, a state senator was arguing for what he called "sane lanes." He thought the ramp meters were impeding the flow of traffic —- one of those things that was making traffic worse. So they shut off the ramp meters for a couple of weeks and crunched the numbers and found that the situation had actually gotten worse, so they turned the ramp meters back on.

People don't like to wait on the ramp. They would rather be allowed to just join the scrum, if you will.

To them it just looks like they're being held up and the highway might even look like it's moving. As an engineer told me in Los Angeles, the reason it looks like it's moving is because we're making you stop.

The key message is there's often a conflict in what is optimal for the individual and what is best for the system. The highway as a system moves more cars at 60 miles an hour, per hour, than if, on that same highway, the cars were going 80 mph.

For each driver, 80 miles an hour would be great. It would get them home faster. But as a system, it's going to be more efficient at the slower speed.