ST. PAUL — Dorian Grilley slows down whenever he sees a white bike.

The bikes — known as “ghost bikes” to commemorate bicyclists who have died in traffic — are spreading across the metro area. Put along roadsides, they serve as grim reminders of the hazards of inattention.

“When I see these, I think about the victims and their families,” Grilley, director of the Bicycle Alliance of Minnesota, said. “It reminds me of the need for driver education.”

The number of the bikes has apparently been increasing since a ghost bike was used to commemorate Jose Hernandez Solano, a bicyclist who died after he was struck by an SUV on Nov. 26.

Someone put up a ghost bike where the incident happened at West Seventh Street and Grand Avenue in St. Paul. Thousands of bikers and drivers have seen it, and since then, other ghost bikes have appeared.

In Newport, a ghost bike sits near the entrance ramp to westbound Interstate 494. That’s where a truck hit bicyclist Peter Morey, 39, of Cottage Grove. After he died in May 2017, his brother put up a ghost bike at the intersection, according to Morey’s wife, Krista Morey.

The bike is propped against a phone pole, flowers now wilted in a water bottle, with photos of Morey clipped to the frame. It is locked in place with a bike chain.

Ghost bikes first appeared in St. Louis in 2003, according to the website ghostbikes.org. The website says there are more than 630 ghost bikes in 210 locations worldwide, but doesn’t say when the tally was made.

Bicyclists nationwide — including Minnesota — have organized memorial rides from one ghost-bike location to another.

The bikes are a form of folk art, impromptu roadside memorials. Some include names and photos of victims, or containers for flowers or other decorations.

They are difficult to count because there are no rules for setting them up. They are spontaneous monuments of grief that sometimes remain for a day or two, sometimes for many months.

The Minnesota Department of Transportation has an uneasy relationship with ghost bikes, or any other type of roadside memorial.

A copy of the department policy, provided Jan. 9, says all memorials are illegal on freeways.

On other state highways, they will be permitted for six months. They will be removed if they slow down the flow of traffic, interfere with maintenance, or if they would be hazardous if hit by a vehicle.

The transportation department said that installing the memorials poses another set of worries — with vehicles parking illegally and disgorging pedestrians along busy roads.

Jeff Lathrop, retail manager of Cycles for Change bike shop in St. Paul, said whether biking or driving, the ghost bikes serve as a warning.

“It is a reminder to keep your eyes open,” said Lathrop. “It’s a reminder that life was lost due to a careless situation.”

The Bicycle Alliance’s Grilley participated in the bike ride in honor of Solano, and has seen the two-wheeled memorials elsewhere.

In fact, he almost became eligible for one himself — when he was nearly killed in a crash eight years ago.

“I was three weeks in the hospital, and it cost $350,000 to screw me back together,” said Grilley.

That made him more aware than ever of the importance of bike safety. “People drive too fast, and take too many chances,” he said.