If three lanes are bad for the morning rush hour on Interstate 40 near the U.S. 70 Clayton Bypass, maybe two lanes will be better.
That's the counterintuitive theory behind a six-week experiment the state Department of Transportation will launch this weekend. The guinea pigs will be thousands of Triangle commuters.
DOT engineers are trying to smooth out a morning bottleneck that snarls traffic where westbound I-40 swells to three lanes at the U.S. 70 interchange in southeastern Wake County - and then returns to two lanes.
To eliminate the frequent backups that start where the third lane ends, DOT will eliminate the third lane.
The added lane runs for nearly two miles, and Triangle-bound drivers naturally take advantage of it. The trouble comes when it ends and they have to squeeze back into two lanes.
"You have some people that wait to the last minute to merge over," said Kevin Lacy, the state traffic engineer. "They'll often move into small gaps in traffic, which causes the cars behind them to hit their brakes and slow down or even stop."
As a result, Lacy said, the morning drive on that two-mile section of I-40 can take 2 minutes on some days, and 15 minutes on other days.
So DOT crews will be out there Sunday morning painting new stripes and setting out orange barrels.
Just where the third lane starts now on the outside, they will shift both existing lanes of westbound I-40 one lane to the right. The existing inside lane will be blocked off from use.
And where the third, outside lane ends about two miles up the road, the two travel lanes will be shifted back to the left.
This stretch of I-40 is one of the Triangle's worst rush-hour bottlenecks. The morning congestion grew worse after DOT opened the Clayton Bypass (exit 309) in 2009.
I-40 is wider near the new interchange, and then it returns to two lanes for three more miles. After passing U.S. 70 Business (exit 306), it becomes three lanes wide again.
DOT is planning a $133 million project to widen 11 miles of I-40, from N.C. 42 in Johnston County to Raleigh's Beltline, but construction is five years away.
Meanwhile, Lacy said, it will cost about $30,000 to get rid of that third lane.
Most of the expense will be maintenance - keeping those orange barrels in place during the six-week experiment.
Traffic computer models suggest that cutting out that third lane will make I-40 flow more smoothly most mornings, Lacy said, speeding the average trip by several minutes.
If the experiment fails, the barrels will roll away and the third lane will return.
One I-40 commuter thinks getting rid of that third lane is a really dumb idea.
"They need to build more roadway, not limit what's there," said Amy Vann, who drives from Clayton to Cary each morning. "People are using what's there because it takes so long to drive. The traffic is horrible, and it's way past due to be three lanes the whole way."