Hundreds of thousands of gallons of concrete were poured overnight above Interstate 5 for what will be a bridge connecting a trolley route from Downtown San Diego and the University City area. 

The Mid-Coast Trolley Project will add nine new trolley stops to the UC San Diego Blue Line, but to complete construction by the projected 2021 date, crews needed to close down a portion of I-5 Monday night into Tuesday morning.

While the interstate was shut down, crews conducted their largest concrete pour to date -- 605 cubic yards of concrete, which amounts to more than 320,000 gallons -- for a future overpass just south of Nobel Drive.

"To put it in perspective, it’s the equivalent of filling four-and-a-half Olympic-sized swimming pools with concrete," San Diego Association of Governments (SANDAG) spokesperson Frank Owsiany said. 

Owsiany said the overnight construction work is difficult and often goes unoticed by the majority of San Diegans.

"I think they would appreciate it a little bit more if they could come up here and they see how hard these guys work and how dangerous it is," he said. 

Motorists were asked to plan an alternate route through the La Jolla/University City area while the interstate was closed for construction.

Northbound I-5 lanes were completely closed from 11 p.m. to 3 a.m. from State Route 52 to La Jolla Village Drive. Motorists were rerouted along eastbound SR-52 to northbound I-805, where they rejoined I-5.

Lane reductions were also in place from 9 p.m. to 5 a.m. on southbound I-5 from La Jolla Village Drive to Gilman Drive/La Jolla Colony Drive.

Construction on the Mid-Coast Trolley Project began in 2016 and in late-March reached a milestone with half of the project completed. Full completion is expected in late 2021.

Owsiany said crews were on budget and on schedule. 

The Mid-Coast Trolley construction project is expected to cost $2.17 billion and will extend the UC San Diego Blue Line another 10.9 miles to the University City with the last stop being the UTC Transit Center.

A large chunk of the funding for this project came from TransNet, the half-cent sales tax approved by voters. TransNet will also provide operating funds for the Mid-Coast Trolley through 2048.

Once the project is completed, SANDAG expects about 20,000 riders every weekday. 

To learn more about the project, visit this website.