A major problem with your idea about self-limiting vehicle speeds is that speed limits are usually safe driving speeds under ideal conditions only. Speed itself

A major problem with your idea about self-limiting vehicle speeds is that speed limits are usually safe driving speeds under ideal conditions only. Speed itself isn't really the problem, but rather poor judgement and unsafe driving habits (often including speeding). Speed is also an interesting topic in that speed limits are often kept artificially low in order to generate revenue. Any automated system to force cars to respect limits would likely meet resistance from municipalities that are dependent on traffic fines for revenue. High speeds are allowed on highways in Germany, but only in certain areas, and German drivers are extremely disciplined with regards to lane changing and the 'hierarchy' of the road. However, traffic deaths are lower than the US, even when adjusted to reflect deaths per km traveled. Driver discipline and skill undoubtedly play a role here, but infrastructure quality and maintenance (and urban planning!) is also a big issue. US roads are comparatively poorly designed and maintained, and outdated engineering and planning practices are still widespread (widening streets and removing barriers instead of using traffic calming--perhaps counter-intuitively, the former causes more serious accidents by encouraging speeding and disengaged driving). I tend to think that at least in urban areas of the US, ditching zoning and onerous anti-alcohol laws (i.e. putting pubs within easy walking distance of where people live) would drastically cut down on drunk driving. Rural areas are of course different. Just my two cents