BRENTWOOD -- An addition to a Highway 4 widening project here may further untangle traffic tie-ups and increase traffic flow through the corridor.

Contra Costa transportation officials recently shuffled money around to construct a second bridge overcrossing at the Sand Creek Road interchange. That decision will allow for an additional two lanes of traffic through much of Brentwood by the end of 2014, as the point on the freeway where traffic funnels from four lanes to two will move about a mile to the south near San Jose Avenue.

"I'm just elated. It's really going to open things up," Brentwood Mayor Bob Taylor said.

The $32 million project to add on- and offramps at Sand Creek and widen Highway 4 from two to four lanes from Lone Tree Way is ahead of schedule and under budget by about $2.3 million. But, that money is allocated from the state through Proposition 1B and would be lost if not used by the end of the year, said Amin AbuAmara, senior engineer with the Contra Costa Transportation Authority.

So, the idea of adding the second overcrossing for $7.3 million, originally thought to be too expensive to include in plans, is now on the table.

The county transportation authority and East Contra Costa's transportation planning group both gave the go-ahead this week for the change order to move $5 million from another project to fully fund the bridge.

AbuAmara said the addition will save about $2.5 million, as temporary dividers and other interim measures between Sand Creek and Balfour Road would not have to be installed.

"This all allows us to truly finish the job," Taylor said. "I might just see it completed in my lifetime; it's all becoming a reality that at one time seemed far off."

The money for the bridge, taken from the account for the Highway 4 widening project through Antioch, will be shifted back later this year.

Work is currently being done to incorporate the second bridge design into the project. Adding dirt embankments for the overcrossing could start by late October, AbuAmara said.

Meanwhile, construction continues this week as contractors with Bay Cities paving and grading put down hot mix asphalt on the future eastbound Sand Creek off-ramp, work on signals and lighting and put up guard rails.

The plan is for Highway 4 traffic to shift new alignment by late September and finish the work by the end of the year, AbuAmara said. That means no more three-way traffic stops at Sand Creek. ¿Right now, traffic on Highway 4 often backs up for miles at the Sand Creek traffic light, particularly during rush hour. The two-lane road has also caused safety concerns.

County Supervisor Mary Nejedly Piepho of Discovery Bay said she is optimistic that the project and its major traffic shifts will be smooth sailing, but she remains cautious.

"As lanes start to open up, hopefully drivers go through carefully and slow down to get used to it," she said.

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.