The pavement is cracked and riddled with holes. Locked doors, fences and heavy walls line the sides. Pipes and cables crawl along the metal ceiling. There’s some light from lamps, and, every once in a while, some sunlight manages to make it through, but that never quite dispels the darkness.

This is not a scene from the horror movie — it’s just another Chicago street.

Stretching from the western tip of Wolf Point to the foot of Trump Tower, Carroll Avenue is almost completely buried underground. Thousands of people walk above it every day without ever realizing what lies under their feet. There have been several proposals to use Carroll as either a streetcar or a bus rapid transit tunnel, but none of those concepts went past the early planning stages.

Chicago has many multi-level streets. As the city was built up over the years, a new level would be erected atop a ground-level street, and the old street would be buried. Wacker Drive is the most prominent example of this.

What sets Carroll apart is that, when an upper level was built, it didn’t become a street. Instead, buildings were built on top of it, effectively hiding most of the street from view. Even the two sections that weren’t covered over are several feet below the surrounding streets, setting it apart from the rest of the Chicago street grid.

Carroll lies at about halfway point between Kinzie Street and northern shore of the Chicago River. It begins at the foot of a disused railroad bridge and continues under the Sun-Times building and the Merchandise Mart. Between Wells Street and Clark Street, Carroll is largely uncovered, moving between older buildings and new skyscrapers. Once it reaches Clark, it vanishes under the skyscrapers and continues east, passing under the House of Blues and Marina City buildings before reaching Trump Tower, where it merges with the underground section of Kinzie Street.

For most of its existence, Carroll served as a freight artery. Even now, parts of the rail line that once ran through the middle of the street are still visible. Those tracks were part of a much longer line that extended all the way to Navy Pier, serving the factories and warehouses that lined the shore of Chicago River.

As the industry gave way to residential buildings, the railroad traffic declined until, in 2000, it was abandoned completely.

Although the railroad has been left behind, Carroll still gets plenty of use. Trucks use it to pick up shipments and make deliveries to the buildings above. The same goes for garbage.

When the railroad was active, it used to branch off toward buildings’ loading docks. Many of those spaces have since been converted to parking lots. Some of those parking lots are public, while others are reserved for the residents of the surrounding buildings. The lots don’t take up the entire street, so the cars can enter, exit or pass right through, but those sections can get congested during rush hour.

Carroll also provides a way to transport performers to the House of Blues without attracting attention or tying up traffic. During performances, tour buses and equipment trucks can line up for blocks. The performers enter through a blue door decorated with a mural of crouching, demonic-looking figures.

Even when nobody is performing, the space under House of Blues can be busy.

Other uses for Carroll are more utilitarian. Because the ground is fairly close to sea level, the sewer systems of the surrounding buildings are stretched around and above the street. Several walls have warning signs — drilling too close to them could damage the utilities.

Under State Street, Carroll is right above the Red Line tracks. Walking a few feet south, one can spot an inconspicuous, but clearly labeled emergency exit. If a Red Line train has to stop between the Grand and State/Lake stations, it would serve as one of the evacuation routes.

Ever since the railroad was abandoned, urban planners have been eyeing Carroll for potential transit use. The street gets little traffic, and it bypasses some of the most congested intersections in River North. There have been several proposals to use Carroll Avenue as part of a light rail or bus rapid transit corridor. Most notably, the Central Area Action Plan called for the establishment of a transit corridor that would connect Chicago’s Union Station, Ogilvie Transportation Center, the Navy Pier and all the major intersections in between. However, that part of the plan was suspended indefinitely as of 2010.

Not that implementing the transit corridor would be easy. Since 2002, Sun-Times and Merchandise Mart blocked off the sections that run under the buildings to regular traffic. And, sometime after the fall of 2010, the section between State Street and Trump Tower was barricaded off.

There is also the matter of maintenance. The pavement is weathered and cracked. When it rains, the water seeps through, leaving puddles deep enough to sink a foot. All those issues would need to be addressed before a transit corridor is seriously considered.

For the time being, it’s business as usual on Carroll Avenue. Men and women and business suits walk casually to their cars through the darkened street. Bikers zoom past them. At the nearby building’s loading docks, the workers chat casually as a UPS truck approaches. And up above, on Clark Street, thousands of people walk by, unaware of any of this.

“Carroll Avenue?” one of them remarks. “There’s a Carroll Avenue?”