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Last Updated: May 22, 2018
The following article - and more - can be found in our print edition:
Safety Issues for Cuomo's Tunnel
• Loriann Cody
Friday morning’s bus accident near the entrance to the Lincoln Tunnel where 32 people were injured snarled traffic for hours, even though the buses involved were at the entrance to the center tube. Can you imagine the nightmare if this accident happened in Cuomo's proposed Cross-Sound Tunnel, somewhere in the middle of the 9-mile underwater span?
The New York City Fire Department responded to Friday’s accident at the Lincoln Tunnel. If an accident occurred in Cuomo’s 18-mile Tunnel, would the Syosset Volunteer Fire Department respond? Would Oyster Bay? What happens if the accident occurs in mile 9 directly under the Long Island Sound?
Tunnel safety has been studied for years, and certainly there are longer underwater tunnels than Cuomo’s proposed 18-mile cross-sound tunnel. The Seikan Tunnel in Japan is 33.4 miles with 14.5 miles under the seabed. The Channel Tunnel (Chunnel) which connects England and France is 31.4 miles long, with the longest undersea portion of any tunnel in the world at 23.5 miles. The Songshanhu Tunnel, China’s longest tunnel currently in use is 24.1 miles. What’s different between these three tunnels and Cuomo’s cross-sound tunnel? All three are high-speed rail tunnels, not auto or truck, as Cuomo’s tunnel would be. That difference is key, especially when talking about safety. Conservative estimates have a car traversing the tunnel in just under 30 minutes (40 mph). That's a long time to be in a tunnel.
How do you go about determining if a tunnel is safe enough? How do you determine the amount of risk that is acceptable? The goal is to make surface roads and tunnels equally safe. Dr. Johan Lundin, Technical Risk Director, WSP (the same Canadian company that conducted the Long Island Sound Crossing Feasibility Study for the NY State Department of Transportation) set out to review road data of the last ten years (in Sweden, where the study was completed.) A risk profile was created showing the frequency and consequences of accidents. Lundin’s team was then able to establish that vehicle accidents in road tunnels, when they do occur, have more serious consequences than surface road accidents which means that road tunnels have greater risks than surface roads. Frequency relates to prevention while consequences have to do with reactions. Tunnel design, reducing speed limits, installing surveillance cameras, designing lanes for traffic control, introducing better lighting, etc are ways to reduce the chance of vehicle accidents. However, once a serious accident occurs, especially deep into the tunnel span, there are problems; such as dealing with fire and smoke, and the length of time to dispatch emergency vehicles to the scene.
Then there are safety issues involved with the tunnel creation. The tunnel would likely be constructed using tunnel boring machines (TBMs). Multiple TBMs would excavate through the soil and rock, and would install precast concrete panels to form the structure of the tunnel. Due to the long lengths of the tunnel, it is expected that the machines would mine from each side of the Long Island Sound and meet in the middle. An alternative approach would be to construct sections of tunnel in the middle of the Sound using immersed tube technology. This would require the sections to be cast in a dry dock and towed to the tunnel location. The sections would then be sunk into a previously excavated trench. If used in conjunction with TBMs, this could be the quickest method to build the tunnel, but would likely face significant environmental hurdles.
One such environmental hurdle is occurring right now at the Chesapeake Bay Bridge Tunnel (CBBT), where a new tube is being added. The boring technology used is reportedly creating enough muck to fill “55,000” dump-trucks, muck that recent tests have confirmed is contaminated by the boring process and must be disposed of in a protected landfill. This boring method used at the CBBT requires the use of additives: foams and other substances common to the oil-drilling industry. Those additives are petroleum-based, leaving the spoils tainted with contaminants considered hazardous to health. Their use means that the muck can not be dumped offshore in the ocean, where the excavated dirt from the trenches would normally be disposed.