Are Hurry Calls and Clearance Strategies Needed? – Paul Finch – National Highways

Many of the signalised junctions and roundabouts on the strategic road network (and others) have queue detection at the bottom of the off slips at say 160m from the stopline. At MOVA sites on short internal links the X loop may also be used to provide a queue detect/hurry call. For sites on UTC or SCOOT, there may also be clearance strategies configured, either automatically or manually implemented by operators monitoring via CCTV. Hurry calls and queue loops do not increase capacity. Installing queue loops and hurry calls at a brand newly designed signal installation appears to be an admission of lack of capacity in the original design TSM Chapter 6 8.7.2. “Hurry calls are useful for certain circumstances, but their unpredictability of demand means there is potential for them to reduce the overall capacity of the junction,…….” A queue on an off slip is likely to be caused by exit blocking, a broken down vehicle or a gridlocked circulatory. Implementing a fixed time hurry call may result in a battle between hurry calls  for the slip road and hurry calls for the circulatory. I have been turning inappropriate hurry calls and queue loops off for years, but queue loops and hurry calls continue to be installed as “normal”, without designers understanding or identifying a need.  My argument is, signals are better staying on MOVA or SCOOT, then dropping off onto a fixed time mode with no idea of what is happening around the rest of the junction.