HATFIELD — A 5-mile section of Interstate 91 southbound between Whately and Northampton was closed Monday morning following a fatal crash in the highway median in Hatfield at around 6:25 a.m., according to Massachusetts State Police. Hatfield Animal Control responded and transported the dog for evaluation and care in South Deerfield. Because of the crash, vehicles traveling southbound were detoured onto Route 5 at Exit 32, with the highway closure causing significant backups as vehicles had to merge before the exit. Vehicles that exited onto Route 5 could only re-enter the highway at Exit 27 in Northampton, with an earlier entrance to the southbound lanes in Hatfield blocked off with orange cones. By 11 a.m., the right lanes and exit ramps had reopened, though the left lane remained restricted, according to the state Department of Transportation.