KNOXVILLE, Tenn. (WVLT) -- Four motorcyclists died in wrecks this weekend, and law officers say speed is to blame for three of them.

They say a blocked view likely is what caused the crash that killed Richard Lawson,22, of Louisville.

A car backed out of a driveway and hit him Friday afternoon.

Early Saturday afternoon, Michael Louis Giroux died on "The Dragon" in Blount County, when his bike spilled over an embankment.

Later, Mark Coleman, 41, died after losing control on loose gravel in a curve on Conner Road.

And just after dawn on Sunday, Jeffrey Sears was killed when he lost control of his bike on Pellissippi Parkway about two miles west of Topside Road, and was thrown 30 feet clear of his bike.