Minnesota utility regulators have put Enbridge Energy’s plan to replace its aging Line 3 crude oil pipeline back on track. They voted 3-1 to approve a court-ordered revised environmental review and reinstate two key approvals that the company needs to proceed with the disputed project. That clears the way for Enbridge to obtain two remaining major state and federal permits and some minor permits that it still needs. But environmental and tribal activists _ who say the pipeline would aggravate climate change and threaten pristine water resources _ vowed further court challenges to ensure that the project is never built.