Flags across the country flew at half staff Tuesday in honor of law enforcement officers who have been killed or disabled in the line of duty.

May 15 is National Peace Officers' Day, one day during National Police Week. John F. Kennedy proclaimed the holiday in 1962.

To memorialize fallen officers, police from around the country meet at the National Law Enforcement Officers Memorial Fund in Washington, D.C.  This week, police officers from Howard County are participating in the Police Unity Tour, a bike ride from Howard County to the Memorial. They arrived in Washington, D.C., on Saturday.

The officers and support personnel wear bracelets with the inscriptions of the officers they are memorializing. Seven law enforcement officers have died in the line of duty in Howard County since 1924.

The sixth officer was Scott Wheeler. On June 6, 2007, Wheeler was working traffic enforcement on Route 32 when he attempted to pull a driver over who was going more than 75 mph in a 55-mph zone, according to Howard County Police Chief William McMahon.

Distracted by her cell phone, McMahon said, she struck Wheeler. He died two days later. The driver was fined $310 for speeding and negligent driving.

Last week, the State Highway Administration erected signs on northbound and southbound Interstate 95 to memorialize the seventh officer killed in Howard County in the line of duty.

Maryland State Trooper Shaft S. Hunter died May 21, 2011, when his patrol car ran into a tractor-trailer parked on the shoulder of I-95 south near Route 32.

The sign, said Chaplain Paul Merkle, will serve as "a constant reminder of [Hunter's] service and of the sacrifice that troopers all over the nation face each day."

With reporting by Patch.com editor Elizabeth Janney.