For an robust system I would use multiple data streams including bust status data/beacons/GPS. I've seen busses with offset stations. 3G is necessary for live

For an robust system I would use multiple data streams including bust status data/beacons/GPS. I've seen busses with offset stations. 3G is necessary for live ETA, if you want to get fancy. All these complications, in my view, are worth it if you want a system that works 24/7 and serves thousands of people daily. The HW and SW dev costs are acceptable, but it does need a decent team, depending on what the starting point is and the ability of the team members.