the northeast corridor and increase the number and frequency of speed limit signs. adam reese is at philadelphia's amtrak station for us. good day to you, adam. what's the latest with the investigation into the crash? >> alex, good afternoon. the fbi investigating whether or not there's a pattern here, a link between three trains getting hit with projectiles minutes apart, miles apart. take a look at the three. first 905 tuesday night. the acela train. five minutes later a accept ta commuter train at 9:10. at 9:21 amtrak 188 hit by what officials call a fist-sized projectile through the front wind 'sheed killing eight people. engineers call this getting rock. it's very common along the northeast corridor. so common they actually protect themselves with grills in the front windshield so they don't get hit with projectiles. here's robert sumwalt of the ntsb. >> the this idea of something striking the train is one of the