In 1927, New York opened the Holland Tunnel with an innovative ventilation system; 84 fans still move air through its 8,500-foot twin tubes

Almost a century ago, engineers solved a problem that could have killed every driver passing through the Holland Tunnel. In his book, 'Highway Under the Hudson: A History of the Holland Tunnel,' Robert W. Jackson writes that the most difficult part of constructing the Holland Tunnel was not the tunnel itself. It was figuring out how to keep people alive once cars started driving through it. That question helped shape the tunnel we still use today.

A tunnel that nearly didn't work

No one had built a tunnel this long for cars and trucks before 1927. Ships had open decks. Trains ran on electricity. Gasoline engines, however, give off carbon monoxide, a gas you can't see or smell. It can build up quickly in a confined space and kill within minutes. Engineers Clifford Holland, Milton Freeman, and Ole Singstad had to figure this out before a single car could safely drive through. Physiological and mechanical tests, led primarily by the U.S. Bureau of Mines, told them how much fresh air the tunnel would need, and how fast that air would have to travel. The result was two cast-iron tubes, each 8,500 feet long and 29.5 feet wide, built between 1920 and 1927, according to ASME's own engineering landmark record of the project. At the time, they were the largest tunnels of their kind ever built in the United States.


The fans that made it all possible

The real breakthrough in the tunnel was not digging; it was the air. The ventilation system, as ASME explains, is housed in four ventilation buildings, two on each side of the river, and includes 42 blower fans and 42 exhaust fans. They combine to produce 6,000 horsepower. Stale exhaust air is drawn out through the ceiling and fresh air is blown in next to the roadway. This transverse design was relatively new in 1927, and it went on to become an influential model for tunnels built after it.

Jackson also notes that the system was put to the ultimate test in real life in 1949, when a fire broke out on a truck inside the tunnel, an incident also documented in contemporaneous accounts of the closure and same-day reopening. Rather than shutting the tunnel for good, the fans continued operating during the emergency to help crews control smoke and reopen the tunnel days later. Almost 100 years later, the same basic arrangement, 84 fans, four buildings, one transverse design, keeps air moving through the Holland Tunnel every day.

What decades of exposure really did to people

Here's a question worth asking: did this system actually protect people over the long run, or just look good on paper? Researchers tried to answer that. In a peer-reviewed study in the American Journal of Epidemiology, Frank Stern and colleagues followed thousands of New York City bridge and tunnel officers, many of whom worked inside the Holland Tunnel, over several decades. The study found that tunnel officers had a somewhat higher death rate from arteriosclerotic heart disease than the general population of New York City. Even so, the researchers found no association between time spent working in the tunnel and risk of heart disease. Working in the tunnel itself was not without risk, but certainly not the death sentence feared by early engineers before the ventilation system was designed. That balance, real risk but brought down to a survivable level, is what the fans were built to achieve.

Why should you care about this old tunnel?

There are two big reasons. First, it's a reminder that everyday infrastructure such as subways, airports, stadiums, and hospitals often depends on unseen systems operating around the clock. Few people think about air until it is gone. Secondly, the Holland Tunnel shows good engineering doesn't have to be flashy to last. No artificial intelligence, no digital sensors; just physics, careful math, and a design clever enough that it hardly had to change for a century.

Today, over 30 million vehicles a year travel through the Holland Tunnel. Most drivers don't think twice about the unseen system working to keep the air breathable. But somewhere in those four brick buildings, air is still being drawn in and blown out every 90 seconds, just like it was designed a hundred years ago.