Hurricane Sandy throttled the Northeast earlier this week, and New York City is only just starting to come back to life. I was finally able to get on the subway and return to work this morning (if only because I don’t live or work in Manhattan). Like Hurricane Katrina, 9/11, or any disaster that has struck and crippled a major city, Sandy was an experiment that we would never conduct voluntarily, and it is going to teach us a lot about how our cities work that we’d never have a chance to learn otherwise. The death toll on 9/11, for example, was much lower than it could have been thanks to lessons from the 1993 World Trade Center bombing.

 Williamsburg Bridge, dark on the Manhattan side (Source: CNN)

For infrastructure/transportation geeks like myself, Hurricane Sandy’s impact on New York has been especially instructive. Two of the city’s most important systems—its public transportation and its power grid—have sustained significant damage and are still well below their normal service levels, preventing huge numbers of people from returning to work or even sleeping in their own homes.

In New York, all modes of public transportation were not disrupted equally, a truth obvious to anyone trying to get around the city this week. Taxicabs operated on Monday, the day of the storm’s landfall, as did on-demand car service Uber, although both were surely impossible to catch. MTA buses (which shut down Sunday night along with all MTA rail service) resumed operation on Tuesday afternoon, while the subways and commuter rail lines began staggering toward resumed service on Thursday morning.

The extent to which the hurricane disrupted each mode is an interesting lesson about the resilience of transportation systems. Taxis are the most flexible and resilient: Their service is unplanned and not limited by schedules and fixed routes, and they can go anywhere that demand exists (within regulatory limits). Instead of one agency, the taxi system comprises a plurality of companies and individual drivers. During a crisis, the temporal and spatial patterns of demand shift dramatically and unpredictably, and taxis are well-suited to readjust accordingly, even with minimal advance warning. Of course, there are almost never enough taxis to satisfy demand in these situations—hence the difficulty of hailing one during rain. Additionally, taxis depend upon the road network instead of a fragile rail network. Flooding affected both, but the relative lack of redundancy in the rail system crippled it for days while road closures simply slowed traffic and forced drivers onto alternate routes. Only the short-term closure of major bridges and tunnels truly closed off whole sections of the road network.

Buses, also reliant on the road network, returned to service two days before rail did. Buses are not as flexible as taxis, but the MTA can reroute them as needed and shift vehicles to meet demand. Even at the time of this writing, buses are a better option than trains for a large number of people in New York. The vulnerability of rail transportation, meanwhile, truly showed itself during Hurricane Sandy: The subway system relies on electricity, which failed throughout the region, and is largely underground, making it susceptible to flooding. When both of these problems happened, the wheels came off, so to speak, and subway service has yet to become available for anyone in Manhattan below 34^th Street (and is currently divided into two entirely separate sections). When a rail network fails, it falls harder than a bus network and takes longer to get back up.

Unfortunately, New York’s subways, the Long Island Railroad, and Metro-North carry millions of passengers every day and when they all stop running, no amount of buses, taxis, or other road-based transportation can make up for their absence. The city therefore faces traffic gridlock until the rail fully returns. Under normal circumstances, when trains can run smoothly, they are by far the most efficient way to transport large numbers of people between concentrated origins and destinations, and even in disasters, buses and taxis are not without their limitations: New York and New Jersey are currently facing severe gasoline shortages in the wake of the storm.

For all the criticism of cars as a mode of transportation, though, you would much rather depend on a road network than a rail network during an upheaval like Sandy. The bigger problems with cars, even under normal circumstances, are our dependence on car ownership and the prevalence of single-occupant vehicles instead of road-based paratransit. Road networks themselves are the true fabric of cities, and provide a more widespread and flexible form of mobility than rail will ever be able to, although rail plays a critical role in the greater transportation system. Disasters like Hurricane Sandy make this clear, and they’re rare occurrences, but New York has endured two hurricane-related transit shutdowns in the last 14 months, so perhaps crises deserve more serious consideration in the city’s transportation infrastructure design.