The tunnel is located approximately 45 feet south of the existing at-grade trail crossing of Lynn Street and is 95 feet in length measured portal to portal. The tunnel trail surface is located approximately 18 feet beneath the existing pavement on Lynn Street.
They studied three options. A cut and cover and two "trenchless" options. Cut and cover would be easiest and carry the least risk, costint $1.39M, but it would have the most impact on road traffic. The cost of the trenchless options can't be determined without a detailed geotechnical report.
On the plans below, you can see where the tunnel splits off from the current trail and passes under Lynn to the north of the current crosswalk. On the east side it passes along the old road which should be no problem. But on the west side I think the issue is that the land there is to be developed and the tunnel is not part of that plan.