The U.S. Postal Service says it has cleared the final regulatory hurdle to placing orders for next-generation mail vehicles. That keeps the Postal Service on track for taking delivery of the first of the electric- and gas-powered delivery vehicles next year. Postmaster General Louis DeJoy said Wednesday that the completion of an evaluation required by the National Environmental Policy Act is an important milestone for postal carriers who’ve soldiered on with overworked delivery trucks that went into service from 1987 to 1994. Environmental groups are pushing back, saying the Postal Service should commit to ensuring 100% of the vehicles are battery powered.