MILWAUKEE (CBS 58) — Diesel prices have reached a milestone drivers and trucking companies hoped to avoid, topping $6 a gallon nationwide.

According to AAA, the national average for diesel is now $6.06 a gallon, up from $5.85 a week ago and $3.71 a year ago.

The higher prices are adding to the cost of operating trucks, creating a daily challenge for companies like Polyak Trucking.

"Most drivers out there are actually paying for it immediately before the load's even hauled, so the effect hits the pocket and cash book pretty strong," Polyak Trucking owner Pamela Polyak said.

GasBuddy says disruptions to the flow of fuel are pushing prices higher.

AAA

"Those diesel prices may continue to inch up as attacks and escalations in the Middle East and in Russia continue to impact the flow of diesel," GasBuddy's Patrick De Haan said.

For trucking companies, the cost of diesel is tied to every load.

"To fill up a tank, you're easily going $800 to $900 just to fill up the tank locally, and it can put a huge strain when we're not seeing that money until later on," Polyak said.

Those higher transportation costs can event