There has been some widely-cited research that has been used in evidence of this,5 although most of it has been concerned with shared-use unpaved paths, rather than well-lit, paved, parallel tracks that run alongside roads. Other, more recent research has found that such separated paths are safer, especially on faster rural routes and around roundabouts.6
Certainly the Netherlands, with its extensive network of separated cycle paths and high cycling rates, also has among the safest roads in the world, suggesting that well designed tracks are not incompatible with safety. Some design changes, such as providing separate traffic light sequences for cyclists and moving the stop lines for cars well behind those of bikes can improve safety further. Either way, separated paths encourage more people to cycle, providing safety in numbers for people on bikes.7
(To read more about the research behind the safety or otherwise of separated tracks, see our wiki page: http://www.cycling-embassy.org.uk/node/1872 )