07Small lids, grates and glass in the sidewalk

The short version: Most of the small metal things set into a sidewalk are access points: a cap over a water shutoff, a bolted lid over a groundwater test well, a grate over a storm drain, a box where city cable gets spliced. Some are relics, like London's coal-hole plates and the purple glass vault lights in front of old commercial buildings in New York.⁸⁶¹¹⁴ The label or shape usually tells you who owns it, and none of them are for the public to open. Before you dig near any of them, contact your local call-before-you-dig service; in the US that means calling 811 (Dig Safe in New England),¹ and the paint marks section explains how it works.

What is the small round "WATER" or "GAS" cap in the sidewalk?

What you see: A small round cast-iron cap, a few inches across, in the sidewalk or grass strip, marked "WATER" or "GAS".

It is the top of a vertical pipe that reaches down to a shutoff valve. A curb box is a cast-iron pipe running from the sidewalk down to the shutoff valve on a building's service connection, about 4-6 ft (1.2-1.8 m) below the surface; only its round lid, marked "water", shows.¹¹⁵ The valve at the bottom is the curb stop, and the water utility uses a long key to turn a household's water on or off there.¹¹⁵

A valve box is the same idea on a bigger scale: a sleeve and lid in the street over a valve on the water main or gas main itself, so crews can isolate a section of pipe. Caps marked "GAS" are the gas-side equivalent. Paris has both kinds: some small covers open onto a building's water valve, turned with a long-handled tool, and others onto the gas pipe serving the building.⁹⁴

If your curb box is buried, tilted or broken, tell the water utility; it is their access point to your shutoff. Who owns which part of the service line, on either side of the curb stop, varies by city, so check your utility's rules.

What is the small capped pipe near the house?

What you see: A small round cap or plug, often brass, plastic or cast iron, near a building's foundation or in the sidewalk, sometimes marked "C.O." or "SEWER".

Caps like this are commonly called cleanouts: access points to a building's sewer pipe, where a plumber can run a snake or camera when the line backs up. Location and ownership vary by city, so leave the work to a plumber or the sewer utility.

San Diego County, for example, says cleanouts "look like the end of a pipe with a cap on it" and are usually within 3-5 ft (0.9-1.5 m) of the building, sometimes at the front property line. There, the property owner is responsible for the lateral from the building to the public sewer main, and the cap must stay on tight except during servicing.¹¹⁶

What is the bolted cover with a triangle at a gas station?

What you see: A small flush cast-iron lid, about 12 inches (30 cm) across, held down with bolts, at a gas station or former industrial site. It may be triangular or carry a triangle symbol.

It is the top of an environmental monitoring well, a narrow pipe used to sample groundwater or soil vapor for contamination, often from underground fuel tanks. One typical 12-inch triangular cover uses the "API 1615 triangle design" so tank-truck drivers will not mistake it for a fill point, has flush bolts to limit access, and carries an H-20 load rating so vehicles can drive over it.¹¹⁷ API 1615 is a US petroleum-industry practice, and the source here is a vendor product page rather than the standard itself.

The triangle here has nothing to do with Nashua's triangular sewer covers, described in the manhole covers section.

What does "Don't Dump - Drains to River" on the curb mean?

What you see: A small round metal or plastic disc on the curb beside a street drain, or a stenciled message, often with a fish.

It is a public-education marker. Storm drains carry untreated runoff straight to streams, rivers and lakes, so anything poured in - motor oil, paint, dog waste - goes there too.¹¹⁸ Volunteer and school groups often install them. The University of Kentucky's program, for example, puts medallions on the curb behind the drain, where snowplows will not scrape them off, using adhesive at 40-90°F (4-32°C); it tells volunteers to confirm the opening is a storm drain and not a steam vent, and its newer medallions carry a QR code for reporting pollution.¹¹⁸

In cities with combined sewers, where rain and sewage share one pipe, some drains lead to a treatment plant instead, or overflow to the river in heavy storms. The sewers section of the sister guide explains the difference.

What is the difference between a catch basin and a storm drain inlet?

What you see: A grated opening in the gutter, or a slot in the face of the curb (a curb inlet), or both.

They look the same from above. A catch basin has a sump, a low chamber below the outlet pipe where sand and heavier debris settle out before the water leaves.¹¹⁹ A plain inlet has no sump and passes water straight into the pipe. Many US cities say "catch basin" for any street drain.

Catch basins need emptying. One stormwater fact sheet says they should be cleaned before the sump is 60% full, often twice a year in spring and fall, with a vacuum truck; disturbed sump material can smell of hydrogen sulfide, the rotten-egg smell.¹¹⁹

Clearing leaves and snow off the grate in front of your house helps; reaching into the basin does not, and should be left to the city.

Why do drain grates have bars going sideways?

What you see: A drain grate with bars running across the direction of travel, or in a zigzag or curved-vane pattern, instead of long slots parallel to the curb.

Long slots that run the same way as traffic can catch a bicycle wheel and throw the rider. Bicycle-safe grates fix that. In 1980 the US Federal Highway Administration's "Bicycle-Safe Grate Inlets Design Manual" picked three designs out of 11 tested at the Bureau of Reclamation lab in Denver, judged on safety, how well they took in water and how they handled debris.¹²⁰

If you ride and see an old parallel-slot grate in a bike lane, report it to the city.

What is the metal grate around a street tree?

What you see: A flat cast-iron or steel grille with a round hole in the middle, ringing a street tree's trunk, flush with the sidewalk.

A tree grate covers the tree pit so pedestrians have a level surface while rain and air still reach the roots. Parisian Fields contrasts Paris's tree grates with trees elsewhere hemmed in by impermeable asphalt or brick.⁹⁴ The same foundries that make manhole covers make tree grates; Neenah Foundry lists them among its products.⁹³

A trunk can outgrow the center hole as the tree grows. If a grate is pressing into the bark, report it to the city's tree or forestry office rather than prying at it.

What are the small round iron plates in London pavements?

What you see: A small round cast-iron plate, about a foot across, in the pavement outside an old terraced house, often patterned, sometimes with glass studs or a maker's name.

It is a coal hole cover. Eighteenth- and nineteenth-century terraces had coal vaults under the pavement, filled through a hole with a cast-iron cover usually 30-36 cm (12-14 in) across, too small for a person.⁸⁶ The raised patterns gave grip in the wet; some covers have vents, glass or prism inserts, or concrete "non-slip" fills; most are round, set in an iron ring, and a few are square.⁸⁶

Makers were often local. Alfred Syer of Pentonville Road (1830s-1960s) dominated Islington, and Hayward Brothers of Southwark supplied widely; an 1868 Hayward advert priced a 12-inch solid cover at 2s 9d, a ventilating plate at 3s and a glass "illuminating" plate at 6s.⁸⁶ Shephard Taylor coined the term opercula for them and drew hundreds in the 1860s, and modern decorative plates by Keith Bowler (1995) sit in Spitalfields.⁸⁶

Most coal holes are sealed now. Older US cities have similar coal chutes. In Boston, in April 2023, a resident filed a 311 complaint about an uncovered Victorian-era coal chute in the sidewalk outside 470 Commonwealth Avenue in Kenmore Square; the Boston Water and Sewer Commission replied that the chute was on private property and outside its control.¹²¹

What are the purple glass circles in the sidewalk?

What you see: A grid of small glass discs or squares, often lavender or purple, set into a cast-iron or concrete panel in front of an old commercial building.

These are vault lights (in Britain, pavement lights): skylights for the vault under the sidewalk. Thaddeus Hyatt patented round glass lenses set in cast-iron sidewalk panels in 1845, with a prism on the underside that throws daylight sideways into the space below.¹²² The idea came from deck lights on ships, and vault lights lit some of New York's first subway stations and the concourse floor of the original Penn Station (1910).¹¹⁴ Hyatt later spent much of his wealth on the abolition of slavery.¹¹⁴

The purple comes from manganese dioxide, added to clear the glass, which photo-oxidizes under sunlight's ultraviolet over decades.¹¹⁴ Electric light and upkeep costs led owners to remove many, often replacing them with steel diamond-plate.¹²² In Sacramento, streets were raised up to 14 ft (4.3 m) after the 1862 floods, leaving lit vaults under the sidewalks.¹¹⁴ In New York's SoHo and Chelsea, where basements extend under the sidewalk, the panels glow at night.⁸⁸

In Britain, Hayward Brothers sold plain blocks, bull's-eyes, semi-prisms and prisms in the 1870s, the prisms being dearest and most effective; later versions set glass in reinforced concrete, and another major firm was founded by Hyatt (1816-1901), who spent his later life in England.⁸⁶

What are the metal doors in the sidewalk in New York?

What you see: A pair of hinged steel plates, usually diamond-plate, flush in the sidewalk in front of a store, which fold open onto steep stairs or a freight lift.

These are cellar doors, delivery access to a basement under or beside the sidewalk. In Manhattan's older industrial districts, which had no back alleys, buildings were set back 5 to 10 ft (1.5 to 3 m), with steel grates that opened onto basement stairs for deliveries.⁸⁸ They are common in alley-less older cities.

Walk around an open cellar door, not past its edge; the stairs underneath are steep.

Liability for open cellar doors turns on the facts. In Harrington v Azogues Corp. (2021), New York's Appellate Division, First Department, held a building owner not liable after a pedestrian fell through cellar doors that a tenant's employee had opened from the basement; the court found the closed doors were not unsafe and rejected a duty to provide warning lights or signals.¹²³

Why is the grate on the sidewalk warm?

What you see: A large steel grate or set of slotted covers in the sidewalk, with warm air rising from it in winter.

It is a vent for something underground: electrical equipment, steam pipes, or a transit space. Equipment underground makes heat and gas that need a way out. In New York, Con Edison's vented, latching covers and grated covers are designed to let smoke and gas escape instead of building up to an explosion.¹⁰¹¹⁰² New York also has steam pipes carrying 450-475°F (232-246°C) steam under Manhattan streets.¹⁰³

Con Edison's outdoor dining guidance for New York calls the rectangular sidewalk grates "ventilation (transformer) grates." It tells businesses not to cover or place anything on them and to keep objects at least 3 ft (0.9 m) clear on all sides, because "proper ventilation is critical to the safe and reliable operation of our facilities."¹²⁴

Grates can also become electrified. Con Edison's mobile detectors scan for stray voltage on service boxes, manhole covers, gratings, fences and traffic lights; the utility reported checking more than 750,000 structures and 36,000 underground transformers, and in 2009 it found and eliminated 6,266 sources, 60% of them from equipment it did not own.¹²⁵

What does "TRAFFIC SIGNAL" or "STREET LIGHT" on a small cover mean?

What you see: A small rectangular or round lid, concrete, polymer or cast iron, near a traffic light, streetlight pole or curb, labeled "TRAFFIC SIGNAL", "STREET LIGHT", "FIRE ALARM", "FIBER OPTIC" or "ELECTRIC".

It is a pull box or handhole: a shallow box where an underground conduit run is broken so crews can pull cable through and splice it. The label names the system that owns it, often a city or state department rather than a utility; a "FIRE ALARM" lid belongs to a fire alarm system (see fire hardware). Specifications are set by each state DOT or city. Iowa's DOT, for example, specifies 24-inch (61 cm) round handholes with flush cast-iron covers that have "TRAFFIC SIGNAL" cast on top, and marks fiber vault covers "Fiber Optics".⁹⁹

In Boston

What you see: Cast-iron "Don't Dump" plaques on the curb beside catch basins, often rusted, and state electrical covers along the roads.

Boston Water and Sewer Commission's marker reads "Don't Dump" and warns that storm water flows to a river or the harbor; markers go next to catch basins that drain directly to Boston Harbor or the Charles, Neponset or Mystic rivers.¹²⁶ The cast-iron plaques come from a program begun around the late 1980s, under which BWSC required contractors to install them on new or rebuilt catch basins; they look older than they are because cast iron rusts.¹²⁷ As of 2019 Boston had about 30,000 catch basins and 424 miles (682 km) of storm drains, with sewage carried separately to the treatment plant on Deer Island.¹²⁷

Universal Hub readers report electrical covers lettered MassDPW, MassHighway and MassDOT, the successive names of the state highway agency.⁹⁶

Elsewhere in the world

• UK: Coal-hole covers and pavement lights are the classic London survivors, and historic coal-hole covers are at risk of theft.⁸⁶ British telecom joint boxes are covered in the manhole covers section.
• Paris: Small covers open onto building water valves and gas lines, and tree grates stand in contrast to paved-in trees elsewhere.⁹⁴
• US West: Sacramento's raised streets left vault lights over hidden vaults.¹¹⁴

Report an error in this section