On the contrary this is an extremely risk-averse strategy since it allows the deployment of autonomous cars to be done in a way deliberately minimizes accident risk on a granular basis. In any deployment scenario of autonomous vehicles there are probabilities of crashes given the inputs to the system: the route, the weather, the behavior of other drivers, etc. When I said "known to be safe" I was using shorthand for "given an extensive array of inputs like route, vehicle condition, time of day, weather, known traffic patterns, prior trip logs, etc, does this route have a sufficiently low Bayesian prior of probability of failure to reach the destination safely to justify the use of an autonomous vehicle, and if so, which combination of system/configuration/etc minimizes the risk?"
Consider the alternative: autonomous cars theoretically get no production use and then suddenly go "on sale" for any buyer to use them in whatever route or condition they want. This would result in an extremely chaotic situation where suddenly there is no opportunity for gradual production deployment to slowly find the edges of their capabilities (which in some cases could result in accidents) -- instead the whole buyer-base of autonomous cars would be exposed to those edge cases, in full, from the moment the cars became available.
edit: Also I'm not sure what you are asking about direct knowledge: I'm stating observations of reality that self driving cars are already being rolled out incrementally in places/routes that they are best suited to.