I walk every day, following the same route to get a little exercise during the pandemic. During that walk, I have noticed, and picked up, 44 small metal strips in the street. Most are about 7 inches long, but vary from 4 to 10 inches. Using a digital caliper, they measure 0.026” to 0.034” thick and about 0.114” wide. As a mechanical engineer, I note that they are carbon steel and have a spring temper. They are flat, so they do not stand up and puncture tires. But where are they coming from?

Thomas McBirney,
Columbia, Md.

Answer Man had no idea — and then he found one of these thin metal strips in his neighborhood and recalled that the streets had just been swept. These mystery strips are broken broom bristles from a street-sweeping truck.

The modern street sweeper is a marvel of engineering. Built upon a sturdy truck chassis, the standard sweeper features a pair of rotating whisks, each about two feet in diameter, on either side of the truck. At the back of the sweeper is a large rotating broom, like an oversize paint roller.

The spinning side brooms clean out the gutters and curbs, forcing debris to the center of the truck’s path of travel. The back broom rotates backward, pushing debris onto a conveyor belt that lifts dirt up and into a hopper. There are two side-by-side steering wheels in a street sweeper, so the driver can hug up to a curb on either side.

Howard County sweeps its streets four times a year, said Kris Jagarapu, chief of highways. Last year, 800 tons of debris was collected.

“Our main effort for street sweeping is to reduce pollutants that go into the Chesapeake Bay,” he said. “It takes about three months to go from one end of the county to the other. By the time we’re done with sweeping, we start again from the eastern end and work our way all the way to the other end.”

The county once owned and operated its own street sweepers, but the cost to buy and maintain a fleet was so great — a well-equipped unit can cost upward of $320,000 — that Howard now contracts out the work to B&J Sweeping & Sons of Baltimore.

Owner Barbara Kestner has a fleet of 15 sweepers, including Elgin Broom Bear sweepers. She also has vacuum sweepers, vehicles that in addition to brooms have vacuums that suck up dirt.

The mechanics of a side broom are pretty complex, since the whisks must be raised and lowered, their angles adjusted. Over time, the bristles wear down and must be replaced, Kestner said.

Bristles on brooms come in various materials, including steel, wire and nylon. If a broom is pushed hard against a curb, metal bristles can break. That’s why airports prohibit sweeping with steel bristles.

In addition to cleaning neighborhood streets and parking lots of accumulated dirt, sweepers such as those from B&J clean the ground-up asphalt or concrete from roadways that are being milled. They sweep up leaves, too, though Kestner said that can be the hardest job of all. Dry leaves fly all over the place. It’s easier if the leaves are a little wet.

Eyewitness views

That 1945 Bethesda plane crash Answer Man wrote about last week? Bill Offutt saw it. He was 14, his family living in a house on East-West Highway.

“I was washing the family car and heard them coming,” Offutt said of the powerful Navy Grumman Hellcats. “They came over the middle of Bethesda, pulled up and rolled, one right behind the other. Then there was a terrible sound, like a bunch of trash cans falling down the steps or something.”

That was the sound of Ensign R.J. Juhl’s propeller slicing the tail off Lt. j.g. C.W. Arnott’s plane, which landed in a fireball in a vacant lot near People’s Drug.

“I got my little plastic Brownie camera, ran up and took pictures until they chased us all off,” Offutt said.

When Offutt grew up, he taught history in Montgomery County and wrote the 1996 book “Bethesda: A Social History.” His research included chasing down both Arnott and Juhl and interviewing them decades after the crash.

“They were playing,” Offutt said. “They were young pilots with great, big, fast airplanes, and they were having a wonderful time.”

The pilots told Offutt that on the morning of June 30, 1945, they’d flown in formation from their base in Norfolk to Atlantic City, where one had a girlfriend. After buzzing the beach there, they returned to Norfolk.

“In the afternoon, they came to Bethesda, where the other one had a girlfriend at the hospital,” he said. “They flew together out to Rockville and came down Rockville Pike at treetop level, then buzzed the Navy hospital at about the height of the flagpoles.”

And then, disaster.

“It is an incredible story, because that was practically the only vacant lot in Bethesda at that time,” Offutt said. “If it had hit anywhere else, it would have caused a lot of damage.”

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/john-kelly.