Reasons against cycle tracks

The new DfT Local Transport Note on Shared Use Routes for Pedestrians and Cyclists is quite succinct in explaining this problem:

"A common reason for taking cyclists off the carriageway is the perception that it will improve safety. However, it is important to understand that a shared use route will not necessarily be safer than an on-carriageway alternative. In particular, careful consideration is needed where a cycle track running alongside a road crosses side a road [sc: a side road]... At these locations, there is significant potential for conflict, which can sometimes negate the safety benefits of segregating cyclists from motor vehicles."