That doesn't make any sense. The point of using a bridge is to reduce cost by reducing the amount of tunneling. Running the train under the bridge means that the train would need a lengthy tunnel under Crescent Heights, since it would be 35m below Centre St. It would also make the 9th Ave stop impractical, would introduce a level train crossing on Memorial, and would mean that the tracks are in the 100 year flood plain (since the lower deck flooded in 2013); you'd also probably need to demolish at minimum the Chinatown Seniors Centre to make the turn onto the bridge. But none of this matters, since the clearance is only 8.7 feet and a low-floor LRV is closer to 13 feet above the rail.