An unusually high number of motorcycle deaths on Minnesota roads this year has authorities cautioning riders and others who drive that they need to share the road.

There have been 13 deaths of motorcycle riders so far this year in the state, the Department of Public Safety said Wednesday. That compares to five at this time in 2011.

Seven of the 13 this year came in May, the department said.

"Nearly half of all motorcycle crashes involve another vehicle," said Bill Shaffer, program coordinator for the department's motorcycle safety center. "The most common factors attributed to other drivers are inattention and failure to yield the right-of-way."

This week, the safety center is initiating a campaign featuring a new TV spot that dramatically illustrates the life-threatening consequences that can occur when drivers are unaware of motorcyclists.

The campaign also revives the iconic bumper sticker "Start Seeing Motorcyclists" -- developed by the safety center in 1985 -- which will run on the sides of buses and on billboards in the Twin Cities area, Duluth and Rochester.