Collisions are the realised violence of the car system whose avoidance generates car's excessive space demand like the wide deference circle round a thug. They are inevitable as cars are autonomous, nothing prevents the simultaneous decision of 2 drivers to occupy the same space, and cars are faster, heavier and more inert than animals and such decisions cannot be as effectively amended, collisions are minimizable by reducing autonomy via rules and streams; but inevitable without overriding autonomy (more 1). Minimizing collisions of autonomous vehicles is simply a matter of reducing the number of vehicles.
Collisions have high social, economic, physical & psychological costs: repair, replacement, relocation or disposal of vehicles; repair of damaged property; trauma and protracted hospitalization or welfare of casualties. The para-olympics games' massed amputees and paraplegics gives a better image than the road toll of the carnage's scale, and many countries have collision compensation systems costing up to 3% of GDP, the pay-outs often invested in new cars in a vicious circle of cost.
Indirect costs are even greater; human death and injury are economically incalculable but minimizing collisions incurs huge spending on road maintenance, traffic lights and signage, policing and management systems. The danger discourages and inhibits walking, running and cycling, (more 2) leading to illnesses from inadequate exercise and obesity (more 3) which have overtaken smoking related illness as the developed world's major morbidity group, hence most expensive in hospitalization and productivity losses.
The changeover from horse to automobile wasn't natural and the same rights and behavioural mores shouldn't apply, carriages had horse intelligence and self preservation instincts to minimize problems, in cars momentary driver inattention can explode as fatal consequence. Car driving is an extreme situation, that's it's excitement attraction; but made common it ceases to be recognized as extreme and currently the danger a driver poses is a matter of denial, the system is psychologically desensitised to these dangers and any responsibilities imposed upon drivers are disproportionately light, leading to too lenient penalties for injurious and fatal collisions and consequent erosion of legitimacy of legal institutions. Large numbers of current drivers are actually unfit to drive, even by current lenient standards, factors which contribute to this are: alcohol; recent research (note 1) has revealed that most tranquillizers are almost as bad as alcohol in impairing response-ability, also some strains of "poly-pharmacy" that western people of advancing years increasingly exist under can be expected to deliver some incompetents. Widespread unreasonable weighting of rights and responsibilities even warps good instincts into harmful forms, some adopt crude self discipline to prevent fatal consequences, resulting in stress, and the widely disregarded sense of life and death pressure is sublimated and then displaced into adrenalin heightened extremism in other behaviours, family violence, road rage, or general unreasonableness.
In every time honoured civilised activity such life endangering roles are only given to trained professionals on duty, so one would expect that current driving conditions will not be "time honoured" by civilization, that the car culture will prove a barbaric interlude and future people regard our road conditions the way we regard the open sewers and cesspits of the last centuries, disgusting and unhealthy, but because of noise, turbulence and physical threat, not odour and bacteria. Urban driving need become a restricted profession, and motor vehicle numbers be accordingly reduced.