As I recall, within the last couple of years a jogger was killed as she did a u-turn in front of a cyclist on a trail in Dallas (Katy Trail, a place well known for robberies and other criminal activity). She was wearing ear-buds connected to an iPod and may not have heard the bicyclist approaching. A few weeks later the city of Dallas put up speed limit signs, I believe it was 15 mph, which really had no effect as there was no ordinance authorizing them so no enforcement action could be taken.