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