PHILADELPHIA—State police have opened a driving under the influence investigation following the deaths of two Pennsylvania troopers and a civilian struck by a vehicle on an interstate in Philadelphia early Monday, state police said. Trooper Martin F. Mack III and Trooper Branden T. Sisca were dispatched after a man was reported walking in the southbound lanes of I-95 near the sports stadiums in South Philadelphia, Capt. James Kemm said. The troopers arrived around 12:45 a.m. Monday and were trying to take the man into custody and walk him back to their vehicle when another vehicle “traveling at a high rate of speed” struck all three, Kemm said. “The impact was so great that it threw the troopers over into the northbound lanes of Interstate 95,” Kemm said. The vehicle ended up on the right-side shoulder of the highway and the driver remained at the scene. Other arriving troopers found witnesses …