It could work here in Oxford if you had a couple of sensible routes which had inter available ticketing from feeder buses.
Woodstock to the city centre via the airport, Kidlington and the Banbury Road.
Cowley Centre, out through the business park to the ring road, along the cycle path (which could be replaced fairly easily by linking other paths along the inner edge of the bypass), through Headington past the Nuffield Orthopaedic Centre, then down the London Road past Brooke’s University, over Magdalen Bridge, and on to the centre.
A route from the south, starting in Abingdon, using the railway alignment to Radley Station, parallel to the railway line past the park and ride, and then parallel to the Abingdon Road, before crossing the Thames on a new bridge, with the line splitting, the inbound one up the side of the Westgate, the outbound one down St Aldate’s.
The eastern route would come in from Witney, along the side of the A40 to Eynsham, cross the Thames and follow the road to Botley, and then up the Botley Road to the Centre.
Within the city centre each route would join a circuit and trams would alternate their routes. (ie: Woodstock to Abingdon would be followed by a Woodstock to Cowley etc…)
This would cover most of the main traffic flows without jamming the Cowley Road, and would cover 3/5 park and ride sites. The other two could have a bus shuttle to the nearest tram stop.
It would also increase the population served to more than twice that of Oxford itself.
To make it work there would need to be strict bus/tram integration and a huge cut to the number of services running into Oxford centre. For passengers travelling from Witney, Eynsham, Abingdon and Kidlington, many of whom work on the opposite side of the city from their homes, it would reduce their commuting time hugely.
I know it is very unlikely, but it could work, and really enhance people’s lives here.