The structure is the Monitor-Merrimac Memorial Bridge-Tunnel (MMMBT), a 4.6-mile long combination bridge-tunnel system
The MMMBT opened in April 1992 after seven years of construction and a total cost of about $400 million.
Salient features of the bridge are:-
1. It is 4,800 feet long from portal to portal.
2. Built by the immersed sunken tube method
3. The traffic lanes in the tunnel are 13 feet wide, with
2.5-foot-wide ledges on either side of the roadway, and with 16.5 feet
of vertical clearance from the roadway to the ceiling.
4. Traffic flow is monitored from a traffic management center where
employees keep an eye on operations through 33 closed-circuit television
cameras.
5. Seventy-two sensors in the pavement of the tunnel and approach
bridges automatically check every 20 seconds for interruptions in
traffic flow. In the event of an incident, motorists are advised of
alternate routes via 32 electronic message signs activated immediately
from the traffic management center.
6. While traveling through the Monitor Merrimac, motorists do not
lose their favorite local radio station while in the tunnel. A
communications system rebroadcasts all local AM and FM radio stations.
In the event of an emergency, tunnel staff can override these broadcasts
with emergency information motorists receive through their vehicle’s
radio without changing stations.
