With the BART’s 10-mile extension from Fremont to San Jose’s Berryessa Station set to open later this year, empty trains have been traveling along the stretch for equipment tests. And as construction winds down, attention is turning to the massive challenge of tunneling under Downtown San Jose to construct the next six miles to central San Jose.

The tunnel project could clog up traffic on the busy Santa Clara Street, while also driving customers away from local businesses and costing the Valley Transportation Authority (VTA) $500 million in extra money. But depending on whether construction teams build one or two subway bores, there may be a way to mitigate these concerns, according to a Mercury News report.

The VTA recommended a single 45-foot diameter subway bore, carrying two tracks within one tunnel. This project would be cheaper to build and less disruptive to the surrounding community, according to the VTA.

BART, on the other hand, prefers two single-track 21-foot tunnels. The twin-bore design is used by most transit systems, and BART officials believe this approach prioritizes safety.

The VTA has yet to vote on the two options. A recent board meeting was canceled so that officials could meet with BART and hash out certain details. The vote will be held at a later date.