Complex sentence: In 2008, Maryland had planned to require that all new signals have flashing yellow arrows; however, their new state MUTCD prohibits the flashing yellow arrow in favor of the flashing red arrow Maryland has used for years.
Split into simpler sentences: In 2008, Maryland had planned to require that all new signals have flashing yellow arrows. But their new state MUTCD prohibits the flashing yellow arrow in favor of the flashing red arrow Maryland has used for years.