Eng's district includes Alhambra, which has long supported plans to extend the 710 to the Foothill (210) Freeway in Pasadena. The 710 now ends at Valley Boulevard, leading to heavy traffic on surface streets in Alhambra.
"The tunnel option would decrease the environmental impact felt by residents in my district with each passing day the gap is not closed," Eng wrote in a letter to the MTA.
Eng also argued that closing the so-called 710 gap will improve regional air quality by shortening routes for hundreds of thousands of drivers. He said the project would help the area reach greenhouse gas emission-reduction targets set by the California Air Resources Board.
Last week, Schiff asked MTA to spike the study of the tunnel, saying the costs likely will exceed the current $5.6 billion estimate and that many people in the region don't want to see the connection built.
La Cañada Flintridge City Council member Laura Olhasso said that she wasn't surprised that Eng would send a letter in support of the tunnel.
"He represents Alhambra and Monterey Park , so of course he would," said Olhasso.
Still, Olhasso said that Eng's statement can be viewed as a sign that the tunnel's proponents are worried about a groundswell of opposition that has built in the last few months. While La Cañada, Glendale and South Pasadena have long opposed an extension, recently the Los Angeles City Council took a vote formally opposing it.
Pasadena city officials are looking for a way to switch a position adopted in 2001 favoring the extension of the 710.
"I think momentum is gathering greatly in opposition of the tunnel, and of course the other side is going to marshal the arguments for it," said Olhasso. "But I'm thinking the momentum is on our side at this point and I'm hoping we can use that momentum to push through and get the Metro board to shut down this project."