US Subways Build Too Many Cross Passages

I wrote the following piece for IFP’s Transit Abundance Playbook , a collection of 15 ideas to improve transit delivery in the US. American transit costs and timelines are substantially higher than those of other developed countries: Spain builds tunneled subway for ~$200 million per mile, while New York spends billions; China built an entire network of high-speed rail while California was failing to connect Bakersfield to Merced. This playbook draws on the past decade of research into the causes of these overruns by groups like the Transit Costs Project and the Eno Center , translating it into practical solutions that could be adopted by policymakers. The full playbook is available at ifp.org/cheaper-transit . Summary US subway construction follows the NFPA 130 fire safety standard, which mandates cross-passages — side tunnels that connect adjacent train tunnels — every 800 feet. This spacing is significantly closer together than European cross-passage spacing requirements, adding to construction costs without measurably improving safety. NFPA 130 requirements should be changed to align more closely with European cross-passage spacing requirements, or agencies and jurisdictions should modify these standards themselves when adopting NFPA 130 or requiring compliance. Problem The construction of anything, be it a new home, an office building, or a subway tunnel, is governed by a series of codes and standards that dictate how it should be designed and built. These codes specify performance requirements (e.g., a residential floor must support a certain amount of weight) and analysis methods (e.g., the capacity of a concrete beam should be calculated using a specific formula), and determine which materials or components must be used (e.g., buildings of certain heights must be made of steel or concrete). These requirements vary across countries — or even regions — depending on the codes and standards adopted in a particular jurisdiction. Often, these requirements are intended to keep occupants or users of a piece of infrastructure safe and ensure that a building won’t collapse during an earthquake, be blown away in a hurricane, or burn rapidly in a fire. Subway systems, like other parts of the built environment, are subject to various codes and safety standards. These systems often consist of two or more adjacent tunnels to allow trains to travel in different directions. One code requirement stipulates the maximum distance between cross-passages, the smaller tunnels that connect the larger tunnels together to allow egress from one to another. This is a safety consideration: if there’s a fire in one tunnel, cross-passages allow riders to take refuge by providing access to an adjacent tunnel. Cross-passages are often equipped with fireproof doors to prevent the spread of fire and smoke. US subway systems typically follow the cross-passage spacing requirements dictated by the National Fire Protection Association’s “Standard for Fixed Guideway Transit and Passenger Rail Systems,” more commonly known as NFPA 130 . The National Fire Protection Association is a nonprofit organization made up of volunteer fire safety experts that publishes over 250 codes and standards on various aspects of fire safety. Because the NFPA code (like most US building codes and standards) is authored by a private organization, it doesn’t hold the force of law and is only required when adopted or mandated by a transit agency or jurisdiction ( New York and Washington state , for instance, have incorporated NFPA 130 into their respective building codes). If a mass transit project receives federal funding — as most transit projects do — the Federal Transit Administration (FTA) requires the project to conduct a safety certification, which typically involves complying with NFPA 130. Code requirements can often add costs to a construction project, as they require additional systems, stronger materials, and additional inspections. In the US, there is famously a large jump in building construction costs when going from seven to eight stories, because the marginal story triggers stricter building code requirements. Subway cross-passage requirements are no different. While the primary tunnel for a rail system can be efficiently dug using a tunnel-boring machine, cross-passage construction must be done using other, less efficient methods , such as drill-and-blast (where holes are drilled into the rock, filled with explosives, then detonated) or using a roadheader (a tunnel construction machine with a large boom-mounted cutting head). Cross-passage construction has been described as “one of the most challenging construction stages for any twin-tube construction project.” The UK’s HS2 high-speed rail project suggests that each cross-passage might cost on the order of $1.2 million to construct, and a 2019 geotechnical report from a Dallas Light Rail project s