ST. PAUL (AP) - Democratic lawmakers say a string of recent explosive crude-by-rail derailments nationwide make it necessary to improve Minnesota's railroad network.

Five trains hauling crude oil have derailed since February. Sen. Scott Dibble, a Minneapolis Democrat, says it's "sheer dumb luck" no similar accidents have happened in Minnesota. Seven or more trains haul North Dakota crude across the state daily.

Legislators on Tuesday renewed their call to impose additional taxes and fees on major freight railroads for safety improvements. An annual fee plus taxing train cars and bridges would raise about $100 million annually for railroad crossing upgrades.

Gov. Mark Dayton proposed those measures in his own budget.

The state's largest freight railroad BNSF Railway announced last month it would spend $326 million this year on network improvements in Minnesota.