WMZ still lists an April to September minibus running the single route of 1.5 miles on a loop. Not sure what percentage of footfall this delivers, but does seem to be the sort of service provided at seaside resorts. Not sure where zoos like Cotswold or Whipsnade would chose to run such a service from, pulling visitors as they do from huge, wide catchment areas....
Yes... to make it worth the cost you would need to tap into a waiting pool of people really.