I'd take a railway over a crappy Sustrans path any day.
This is the problem - lack of consistent design and maintenance.
Take Route 6 : between the centre of Leicester and Blaby it's an excellent, well used, well maintained disused railway with an asphalt surface; between Market Harborough and Northampton it's a poor, badly maintained disused railway with 'dust and stone' surfacing.
The Leicester section -admittedly in commuter territory - is used by cyclists, horse riders, joggers, dog walkers etc; the Northampton section - much more rural - only sees a significant amount of use on sunny Sundays.
I'm sure if the Northampton section had a bit of investment there is potential for greater use (cycle commuting from Brixworth; and Park&Cycle into Market H).
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