Construction cost hikes are among the challenges federal officials face in trying to finish 670 miles of fence on the Mexico border by Dec. 31, as Congress mandated. Testifying before a House committee on Sept. 10, W. Ralph Basham, Customs and Border Protection chief, said 344.3 miles of fencing were done by Aug. 29. Pedestrian-fence costs in August were up 88% from February estimates, to $7.5 million a mile, said the Government Accountability Office. Vehicle-fence costs rose 40%, to $2.8 million.