An Irving officer drove up on a gruesome scene overnight. A motorcyclist was killed at the scene when he slammed into the back of a big rig on Highway 183 near MacArthur. The officer discovered the crash even before witnesses were able to call 911. The collision and investigation closed down the eastbound side of 183 for more than three hours. But all lanes were reopened just before 6 a.m., though police cautioned they would remain on the scene for some time continuing their probe.