the existing tunnel is 2 lanes. they're not replacing it, they're adding a second one.
That is clearly correct for the tunnel that is being built now, Thimble Shoal,
the southern of the CBBT tunnels. Seagoing traffic headed for the Norfolk Naval
Station, the Ports of Virginia in Hampton Roads and the Port of Richmond (at the
head of navigation of the James River) all cross the CBBT by way of Thimble Shoal.
At one point early on, there was consideration given to building one new four
lane tube that would carry alll CBBT traffic and abandoning in place the existing
tunnel, but I am not sure that a four lane tube was even considered during the
EIS process that led to approval of the new bored Thimble Shoal Tunnel that is
now under construction (with some difficulty).
The north Chesapeake Tunnel is where seagoing traffic heads north toward the
Port of Baltimore.