At some point however we are going to face the fact that roads are a cheap form of transport because they are shared and so are dangerous - the UK has 4500 deaths a year
Well that’s untrue.
https://en.m.wikipedia.org/wiki/Reported_Road_Casualties_Gre...
As you can see road casualties have been dropping for quite a while, and for the last 5+ years the rate is around 1,700. Deaths per year haven’t been near 4500 since the 90’s. This also reflects another reality you ignore, which is that road fatalities are not evenly distributed. Being drunk, driving tired, owning an unsafe or poorly maintained car, driving too fast, all contribute to risk, and all are avoidable.
You also picked the UK, which has an extensive rail system.