Complex sentence: There have been no serious terrorist threats or attacks on Raleigh public transit in the city's history, however, on May 4,2007 a bomb threat was received at the CAT regional transit call center at about 9:00 am.
Split into simpler sentences: There have been no serious terrorist threats or attacks on Raleigh public transit in the city's history. However, on May 4,2007, a bomb threat was received at the CAT regional transit call center at about 9:00 am.