The hazards of two-wheel travel were emphasized in two incidents Saturday in the Annapolis area as a motorcyclist was killed on a road and two bicyclists were severely injured while on a long-distance bike trail.

The motorcyclist died when he struck a curb and was thrown off his Harley-Davidson, Anne Arundel County police said.

The bicyclists were hit by a car while on the Baltimore & Annapolis trail, where it uses a roadway shoulder.

In the motorcycle incident, police said that Forrest Andrew Williams, 54, who lived in the Annapolis area, was going south on Green Holly Drive, near Ramblewood Drive, when he struck the curb of the median.

Police, who were called just after midnight, said alcohol and what might have been a substandard helmet apparently contributed to Williams’s death.

The bicycle crash occurred about 2:10 p.m. along Route 450 near Brice Road, police said. The cyclists were properly using the right-hand shoulder, which is marked and designated as the B&A trail, police said. As the cyclists headed south, a motorist, also southbound, crossed into their lane and hit them, police said.

The two were flown to the Maryland Shock Trauma Center in Baltimore. Katie Pohler, 23, of Glen Burnie, Md., suffered life-threatening injuries and Todd E. Green, 27, of Severna Park, Md., was seriously injured, police said.

In a statement, police cited driver error as the apparent cause and said that alcohol was a contributing factor.

The 13.3-mile B&A trail is a major long-distance cycling route, running between Glen Burnie and Annapolis.