These "wolf packs" should not be humping down the MUPS. Inappropriate for the narrow lanes.
In Seattle not once did I encounter packs of riders haulin' the mail. Every group of riders were exercising common sense and rode at appropriate speeds for the lanes. In my neck of the woods I stay off the MUPS due to riders moving too fast, walkers walking 4 abreast and dogs on long leashes. It simply ain't safe for bicycles. Stay on the roads or off road if it suits you.