https://www.theguardian.com/cities/2017/sep/19/britains-1960s-cycling-revolution-flopped-stevenage
I have had the...experience...of passing through St Evenage on a number of occasions over the past few years. I have relatives in nearish-by St Albans and St Evenage is the nearest station on the ECML from Edinburgh (it's less convenient these days: since VTEC re-jigged their timetable there are ~no direct services any more). My folks pick me up from and drop me off at the station. Despite all those journeys through the town, I never realised that St Evenage has a network of decent, segregated cycling infrastructure.
Perhaps it is actually too segregated? If people can't see it from their cars, maybe they're less likely to think that maybe they could take the bike instead. And it makes it a lot less obvious that the cycleways can take you everywhere in the town that you currently go in your car.
I have to agree with one of the BTL comments: allowing mopeds to use the cycleways sounds like a very poor idea.
The other issues seem to be maintenance and policing - both victims of endless rounds of public spending cuts since St Evenage was built, fuelled by myopic middle income earning oafs who fall for the lie that tax cuts are for their benefit, rather than primarily helping to shovel even more wealth towards the super-rich.