Some 30 million bricks went into this sturdy relic of railroad engineering. Excavated more than 100 years ago, the tunnel is used now by CSX Transportation, which says it is the largest subterranean conduit of rail freight along the Atlantic Coast.
Most days, about 40 trains pound through this cavern, a 1.7-mile channel of Stygian darkness and dank, musty air infused with a dense humidity born of outside water seeping down the curving masonry walls. Drainage shoulders beside the rail tracks ooze industrial slime.
"Inside there, it feels old. It feels wet and dark. It's definitely got an ancient feeling," said Bob Blanding, a CSX track maintenance worker.
The tunnel's construction bankrupted the Baltimore and Ohio railroad when it was built in the 1890s, and it was lightly used for decades. But that is not the case anymore.
Virtually all the Tropicana orange juice sold in the northeastern United States flows under Baltimore in huge orange refrigerator cars that make up what railroaders call the "juice train." It stretches almost a mile long and carries citrus juice to a New Jersey distribution plant.
Other long trains haul tons of Fila-brand athletic shoes and tank cars full of oil used in Frito-Lay snacks. Jumbo-sized freight cars filled with automobiles, General Motors Astro vans, John Deere tractors and coal all rattle through the tube.
The tunnel also has a second use. An MCI fiber-optic cable trunk line suspended on the tunnel's west wall carries thousands of long-distance phone calls.
Civil engineers consider the tunnel shallow, with not much fill on the top.
At Camden Street, its top layer of bricks is but 3 feet below the surface. At its deepest, at Madison Street, the tunnel is 49 feet below ground.
A single CSX freight track runs in the middle of a rounded cavity covered with a century's worth of coal and foamy-looking diesel soot deposits.
The rail tube runs alongside the cellars of such downtown landmarks as the Baltimore Arena, former department stores, Maryland General Hospital and Howard Street's antique shops.
The entire structure stretches from a point alongside the lots at Oriole Park at Camden Yards to just above the Joseph Meyerhoff Symphony Hall.
The oldest part of the tunnel was built between 1890 and 1895 by a contractor born in Cork County, Ireland, who went on to construct New York's first subway. That original portion was lengthened in the late 1980s to accommodate Orioles' parking and light rail construction.
What was new and marveled at in 1895 is today overlooked, often forgotten by Baltimoreans.
When unveiled by the old B&O railroad, it was the longest soft-earth railroad tunnel in the United States. It also had a world-class status with the first section of mainline railroad electrification anywhere.
The one rail classification that does not go through Howard Street is human -- passenger trains use different tunnels in and out of Baltimore.
Passengers have been shut out of the Howard Street Tunnel since 1958 when the B&O withdrew from running passenger trains north of Baltimore.
Other than railroad employees, students at the Maryland Institute College of Art probably know the tunnel best. Nearly 30 years ago the art school bought Mount Royal Station, an 1896 Romanesque Revival building set in a grassy bowl at the tunnel's northern opening. The Mount Royal platforms are the best spot from which to observe the rushing rail traffic.
It is here that remnants of 1890s railroading are most evident.
An iron-framed train shed arches overhead like a metal tent where catbirds fly in and out. Graceful wrought-iron fencing screens off the rails for safety. There's a stand of wild raspberries growing near the tunnel portal and a cornerstone inscribed with its construction history.
Even the most impatient train spotter is rewarded here:
First there's a slight movement of air. Scraps of discarded paper get lifted off the ground as a train enters the tube at the Oriole Park end.
As the locomotive charges north (there's normally a 25 mph limit here), the engine seems to push air through the cavity. It's roughly the same effect of blowing air though a soda straw.
There's still no train in sight at this point, but air begins to rush out of the yawning, dark space. Then, in the distance, is a sound that resembles the lowest note of a huge tuba. The notes grow more audible until a shaft of reflected light glimmers on the train rail. Soon after, three diesel headlights appear.
It can take more than three minutes for a long freight train to pass through Mount Royal Station, cut through a minitunnel at Mount Royal Avenue and twist under the Jones Falls Expressway and the North Avenue bridge.
While the tunnel is fairly straight, train engineers heading north wince after they leave it and head into a rail corkscrew of reverse curves in the Sisson-26th streets-Huntington Avenue area.
The tunnel's history began Sept. 12, 1890, when tunnel contractor John B. McDonald signed the papers. His results were so well regarded that he was selected to build New York's first subway, the Interborough Rapid Transit (IRT).
"The tunnel was undoubtedly the most expensive project the railroad ever took on. It drove the line into receivership in 1896," said Herbert H. Harwood, a B&O historian who has written several books about this line.
The tunnel was part of the B&O's grand scheme to get its trains through Baltimore to the north from the Camden Station area.
McDonald's construction crews worked a little less than five years on the project, formally called the Baltimore Belt Line, the terminology used for the railroad track girdling Baltimore. The first regular passenger service to Philadelphia and points north began May 1, 1895.
The B&O's attempt to go after the northeast passenger business was not a roaring success.
The Pennsylvania Railroad, its principal competitor in the Washington-New York route (the B&O went only as far as Jersey City), won out.
The Howard Street Tunnel, though an amazing piece of engineering, went down as an all-too-costly exercise in business rivalry.
A 20th-century plan to locate a subterranean platform below Lombard Street didn't pan out either. The rough brick walls and unadorned arches of a stop that never saw passengers remains as an eerie reminder of an aborted corporate decision.
But with major changes in East Coast railroading in the past 25 years, the Howard Street Tunnel has come back strong.
"Now they [CSX] are handling virtually all the freight on the Northeast corridor. It's a much more vital artery than anyone ever anticipated," Harwood said.
LENGTH .. .. .. ..1.7 miles
GRADE.. .. .. .. .. ..1.35 dTC
SPEED LIMIT.. .. .. ..25mph
TIME TO BUILD .. .56 months
OPENED .. .. ...May 1, 1895
History of the tunnel
Until 1884, the Baltimore and Ohio railroad leased a railroad track through Baltimore to connect its eastern and western routes. In 1884, a competitor purchased the track, leaving the B&O with no way to get its trains through Baltimore. The hills were too steep to build a track around the western edge of the city, so the B&O opted to build a tunnel under Howard Street.