The danger in seemingly banal police work of directing traffic and shutting down roadways gained new attention Monday as colleagues mourned an officer who died while working on President Barack Obama's motorcade.

Jupiter Police Officer Bruce St. Laurent, 55, was killed Sunday in West Palm Beach after his motorcycle was struck by a pickup truck while he prepared to shut down a stretch of Interstate 95 ahead of the motorcade.

Outside Jupiter Town Hall, the flag was lowered to half-staff, the fallen officer's patrol car was draped in memorial bunting and makeshift memorials sprang up for friends and colleagues to light candles and leave flowers.

Though the task of keeping traffic at bay while a dignitary passes may seem routine, St. Laurent's death is just the latest in a line of deaths stretching back more than a century in which an officer was killed protecting the president.

"Even at their slowest speed, even at their simplest form, they have many, many unknowns in them," Sgt. Nicholas Onken of the Rio Rancho, N.M., Police Department, said of escorting high-profile figures. "What we do know is that we have a package to deliver safely from Point A to Point B."

Onken has worked on presidential motorcades for Obama and President George W. Bush and his friend, Officer Germaine Casey, died in a crash five years ago while escorting Bush. He said presidential motorcades can carry added risk over, say, a funeral procession, where officers typically would travel at lower speeds.

When the president visits, officers typically "leap-frog": closing down a section of roadway, then rushing past the president's car once he passes to establish new roadblocks further ahead. All of it must be done at a fast pace to ensure the dignitaries are protected.

Accidents involving presidential motorcades date back at least to 1902, when a Secret Service agent was struck and killed by a trolley car in Lenox, Mass., while serving in President Theodore Roosevelt's motorcade. The National Law Enforcement Officers Memorial Fund counts 16 officers before St. Laurent who were killed while escorting a president or presidential candidate.

It's not even the first time such an incident has happened locally. Twenty years ago, when Sen. Paul Tsongas was seeking the White House, a Palm Beach County Sheriff's deputy died in a motorcycle accident while escorting the candidate.

Though such accidents garner far more publicity than similar ones not involving a dignitary, Steve Groeninger, a spokesman for the Law Enforcement Officers Memorial, said police face danger regardless of whom they're protecting.

Traffic fatalities were the leading cause of death for officers killed in the line of duty for 13 of the past 14 years, according to Groeninger. Firearms-related deaths led the fatalities in 2011, but traffic deaths are again the leading cause so far this year.

"There are inherent dangers in all of the calls and responsibilities that law enforcement make throughout their day and throughout their shift," Groeninger said. "It does sound routine, but I would venture to say most officers would say there's no such thing as a routine call."

The Palm Beach County Sheriff's Office and Florida Highway Patrol were still probing the crash that killed St. Laurent and said it could take months before they determine whether charges are warranted.

The sheriff's office identified the driver as Susan Holloway, 56. Investigators say she slammed on her brakes to try avoiding the motorcycle. St. Laurent was thrown from his bike and caught underneath Holloway's truck. A call to a phone listing for Holloway went unanswered on Monday.

Across all fatal traffic cases, officers say a spate of distracted drivers are complicating their work.

"It's a rarity that they happen at these things but it can happen at any event," said Palm Beach County Sheriff Ric Bradshaw, who served on several presidential protection details in the 1970s. "People are just not paying attention."

Tod Burke, a criminal justice professor at Radford University who was once a police officer who assisted with a visit to Maryland by President Jimmy Carter, said distracted rivers add an extra layer of complexity to an already-difficult job.

"The officers who are doing these details have to be even more vigilant, have to be more aware, have to be more defensive than they were in the past," he said. "And then you throw on top, 'Hey, the president's coming.'"

St. Laurent had 20 years of experience, all but two of them as a motorcycle officer, and had worked in numerous presidential motorcades over the years. Sgt. Scott Pascarella, a friend of St Laurent who trained him when he joined the Jupiter Police, said he was always eager to volunteer for such duty.

"He was proud to serve," Pascarella said. "And he was doing what he wanted to do at the time he passed."

Onken, the New Mexico officer, gave the eulogy at his friend's funeral. He focused on Casey's personal strengths and the example he set for others. He didn't mention the honor and nobility he believed Casey showed dying while protecting the president.

"It really didn't need to be said," Onken said.