Oxford's transport system is trapped in a local optimum; it has already been heavily optimised for this and there is no way to improve it by making small changes.
To see this, consider just how badly even quite small changes work. The Hythe Bridge-George St junction was changed, but is clearly too dangerous for people cycling and so is being redesigned again, moving back towards its original layout. Stopping even a few bus routes running down Queen St has proved infeasible because of the effects on congestion in St Aldates. Widening a small stretch of footpath on High St by a metre had such a terrible effect on congestion and cycling safety that it was rapidly reversed. And so forth. Elsewhere, expensive larger-scale changes — the Plain, the Old Rd-Warneford Lane junction, and so forth — have produced minimal improvements, in what I call "expensive incrementalism".
We're also, like the metaphorical frog in boiling water, in a steadily worsening local optimum. Oxford's population is growing. Oxford University has an aspiration "to build at least 1000 new homes for rent which would increase the stock of housing we can make available to staff". There are three or four loft conversions or extensions underway on my street alone; near one end of it Wadham college is building accommodation for 135 students on what was previously a car sales yard; an old light industrial site a few streets away has a "Sold" sign on it... Andrew Gilligan's Running Out of Road report says: "Over the next 13 years, there are to be 85,000 new jobs and 100,000 new homes in the county. 24,300 of the jobs and 28,000 of the homes will be in the city of Oxford itself and most of the others will be nearby. The county council estimates that this could result in a 25% increase in journeys within the city boundary, and 13,000 more car commuter trips each day."
So transport runs at capacity. Driving is limited by congestion and the willingness of people to put up with hour plus commutes each way. Cycling is limited by willingness to deal with a hostile environment and lack of any space. Speed and comfort walking around the city centre are circumscribed by lack of space and motor traffic. Bus routes and reliability are constrained by congestion and the lack of layover space. And when everything is at 98% utilisation in peak even when things run well, there's no slack in the system for anything going wrong, even for predictable maintenance. No mode of transport is reliable and comfortable; every mode is sometimes painful, if not actually dangerous. And things are only going to get worse, for everyone.
The central implication of this is that small changes are not going to help. If we reduce the number of private motor vehicle trips in Oxford by 15%, for example, through a workplace parking levy or a congestion charge, that's not going to be enough to either make peak hour bus trips fast and reliable (and bus lanes unnecessary) or to make cycling an option for any significant number of new people.
One organisation proposing radical changes is Oxfordshire Liveable Streets