Even if those drivers were driving to and from a place on a frequent bus/Metro route, it's not as binary as saying "you should get the bus or Metro instead"... until a time when catching a train further than Chester-le-Street or Morpeth is cheaper than driving, when it doesn't take two bus journeys to travel three miles to a friend's house, or when it isn't awkward (for those not within 5 miles of each!) to get to the Silverlink, MetroCentre or Dalton Park for a bit of retail therapy then barely anyone will switch from car to bus.
When you get a car, you probably won't have enough money for the weekly or monthly ticket that can only be used in the areas you're commuting to and from. People can't afford both, and the car will always win because that's what gets them around after their commutes.
RE: Reversing the decline in passenger numbers