Workmen in Silver Spring check on last-minute details for the Intercounty Connector opening. (Linda Davidson/THE WASHINGTON POST)

The last major link of the Intercounty Connector opened to Laurel early Tuesday, cutting drive times in half for many motorists.

Although official vehicle counts were unavailable, the 18-mile toll road, also known as Route 200, appeared busier than its first, 7.2-mile segment has been since it opened in February. Workers began opening the road shortly after midnight, and all interchanges were open by 12:45 a.m.

Motorists who tried out the new highway during the first day of a toll-free trial period were practically giddy over six lanes of wide-open asphalt.

“I’m smiling! I’m happy!” Stephon Collins said from his hands-free cellphone as he took the ICC from U.S. 29 to I-270 around 1:30 p.m. Collins said his drive from a Silver Spring community that he manages to I-270 near his Germantown office took 16 minutes. It usually takes 35 minutes to well over an hour via I-270 and the Capital Beltway.

“I can get across the county in 20 minutes — I’m loving it,” Collins said.

Dante Searles, a tow-truck driver, said his trip between I-95 and Gaithersburg to deliver a car usually would take between an hour and an hour and a half during the morning rush. His drive on the ICC around 8 a.m. took 45 minutes. He said he hopes his employer will reimburse him for ICC tolls once they kick in Dec. 5.

“I’m always willing to pay for convenience,” Searles said.

Even with the road’s wet pavement shrouded in a dark morning fog, “Everything has been going very smoothly,” said Cheryl Sparks, a spokeswoman for the Maryland Transportation Authority, the state tolling agency that will operate the road.

Authority officials have said they will keep the ICC’s tolls high enough to ensure that the road remains a free-flowing, reliable alternative to congested local roads. But Sparks said the highway might bog down Wednesday during the busy Thanksgiving getaway and the toll-free trial period.

The toll will be $4 each way for passenger vehicles to travel the entire highway during the morning and evening rushes.

How many motorists are willing to pay the tolls will be key, because the state financed half of the ICC’s $2.56 billion in design and construction costs with bonds backed by the state’s toll revenue. Maryland recently raised tolls statewide largely because of debt pressures from paying off the ICC construction and the $1 billion construction of express toll lanes on I-95 northeast of Baltimore.

Collins, the community manager, said he’s willing to pay.

“You look at the time you spend traveling, and it doesn’t feel that expensive,” Collins said.

Not everyone celebrated the opening. David O’Leary, conservation chairman for the Maryland chapter of the Sierra Club, said he remains concerned about the ICC sending storm water rushing into local streams, worsening the region’s air quality and spurring sprawling development in places like Howard County.

“It just allows people to move farther away,” causing them to drive farther, O’Leary said.

Many residents along the route also braced for the sounds of traffic. A tall sound barrier now lines Jeff Owrutsky’s back yard, where his family once looked onto woods from its home in the Tanglewood subdivision of Silver Spring. The ICC is so close on the other side, he said, that “you could throw a water balloon and hit a car from my kitchen.”

Owrutsky said he could hear traffic inside his home Tuesday morning with the windows closed, but he doesn’t expect to feel the highway’s full impact until the weather warms up.

“We’ll see what it’s like in the summer when we’re hanging out on the deck and we see what the atmosphere is like,” he said.

The final piece of the ICC project — feeder lanes along I-95 and a one-mile segment between I-95 and U.S. Route 1 — is scheduled to begin construction in early 2012 and open in spring 2014.