Complex sentence: Hand-held mobile phone usage fell in New York in the five months following the hands-free law taking effect, however it rose almost all the way back to the pre-law level at the 16-month mark.
Split into simpler sentences: Hand-held mobile phone usage fell in New York in the five months following the hands-free law taking effect. However, it rose almost all the way back to the pre-law level at the 16-month mark.