Cyclists on New York City's new, physically-separated 9th Avenue Bicycle Lane are protected from left-turning cars by bicycle traffic signals. Such signals are common in Europe, but a fairly new concept in the US.
The lights protect cyclists from left turning cars, who are only allowed to turn left on a green arrow. (See here: www.flickr.com/photos/kgradinger/2367382978/ )
Feel free to use this photo for other purposes, but please credit to Kyle Gradinger/BCGP.