supporting structure, to its mechanical, electrical, and communications systems, and result in large numbers of occupant deaths and injuries.

Implementation of Existing Technology

Vulnerability to Railcar and Container Contents

Inspections could be increased, perhaps at their points of origin, provided that more personnel are made available and that shippers accept the additional delays. Overall, however, current technology and systems are not adequate to meet this threat. This topic is covered in more detail in Chapter 7, “Transportation Systems.”

Flooding of Urban Tunnels

Urban transit and railroad tunnels that are below the levels of nearby bodies of water are vulnerable to flooding if breached.

Recommendation 8.27: Local authorities should identify and harden sites favorable to the breaching of transit or railroad tunnels that lie below surrounding water levels, and they should increase surveillance of all activities occurring in such areas.

Recommendation 8.28: Once sites are identified, authorities should analyze them to determine their resistance to the effects of explosives detonated either inside or outside the tunnel.

Underground Parking

The vulnerability of underground parking areas could be reduced by limiting the size and carrying capacity of vehicles allowed entry and by making the inspection of suspicious vehicles or containers routine. Although this approach requires that trained personnel be posted at entrances and is thus expensive (to cover training, salaries, and around-the-clock staffing), parking fees could be adjusted to account for the added cost.

Tunnel Ventilation Systems

Both highway and transit systems tunnels serving cities require extensive tunnel ventilation systems for safe operation. The highway tunnel ventilation systems are designed to remove vehicle exhaust fumes from the tunnels and also to respond to a fire or explosion in the tunnel by isolating the affected zone, thus allowing occupants not involved in the event to exit safely. Transit tunnel ventilation systems are primarily designed to perform the isolation function. Terror-

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