MARTINEZ -- Next year, Caltrans plans to seismically retrofit a section of Interstate 680 just south of the Benicia-Martinez bridge and replace an existing off-ramp that has a tragic history.
The $15 million project calls for retrofitting a part of the highway known as the Mococo overhead, rebuilding the Marina Vista off-ramp and providing a one-lane emergency access route on southbound I-680. Construction is scheduled to begin in spring of 2014 with completion in the winter.
The retrofit work is designed to strengthen the overhead so it won't collapse during a major earthquake, though it may still sustain damage, said Hamid Fathollahi, Caltrans project manager.
In the event that an earthquake renders the overhead useless, one lane of southbound I-680 traffic coming from the bridge would be rerouted across the median and into a northbound lane to carry traffic past the damaged section, Fathollahi explained.
The other component of the project involves rebuilding an off-ramp that was the site of a terrible accident nearly 40 years ago.
In 1976, 28 students and a teacher died when a charter bus carrying members of the Yuba City High School choir crashed through the guard rail on the Marina Vista off-ramp, plunged 30 feet and landed on its roof.
Caltrans plans to demolish the off-ramp, which curves sharply, and replace it with a structure with 16-foot-wide lanes to give buses and trucks more room to navigate the turn. Caltrans will close the Marina Vista off-ramp in May 2014 and it will take four to six months rebuild, Fathollahi said.
While the off-ramp is closed, motorists traveling southbound on I-680 who want to get off at Marina Vista will detour to Arthur Road, make a left turn, get back on the highway heading north and exit at Waterfront Road. Fathollahi said the detour will take about 10 minutes.
To ease congestion at the Arthur Road off-ramp, Caltrans will put in two left-turn lanes and temporary traffic signals.
Although Councilman Mike Menesini acknowledged the importance of improving the safety of the Marina Vista off-ramp, he expressed concern about closing it for so long, particularly during the summer months.
The detour will inconvenience people traveling from Solano County to the marina, the sports complexes or the downtown shops and restaurants, he argued.
"This is a huge deal for Martinez. The bottom line is it's going to have a very strong adverse financial impact," Menesini said.
Fathollahi pointed out that Caltrans seismic projects typically don't include improving structures, but the agency is making an exception in this case because it can replace the off-ramp for about the same cost as a retrofit.
But he added that the agency will do what it can to ensure that the off-ramp closure causes as few disruptions as possible for commuters, residents and businesses.
Lisa P. White covers Martinez and Pleasant Hill. Contact her at 925-943-8011. Follow her at Twitter.com/lisa_p_white.