The Utah Highway Patrol is urging drivers to be careful over the holiday weekend after highway accidents made June one of the deadliest months for drivers in almost nine years.

UHP announced Wednesday that 36 people died in traffic-related crashes in June.

That's the highest number of traffic-related deaths since 37 people died in August 2005.

Troopers say the June number is preliminary and could grow because some reports are pending.

Utah Highway Patrol Trooper Evan Kirby said Thursday that officials don't know what caused the June spike but are deploying 270 extra troopers for the July 4 weekend.