You confuse technological advances and safety techniques. These are very different things. Safety techniques are theoretical principles that are used to keep technology safe. Typical examples of safety techniques in systems design are: readback, diversity, majority voting, coding of information.

In the case of establishing the correct position of vehicles, whatever the technology used it will have an error of measurement. This error accumulates over time, especially if you are measuring displacement. You will need reference points to retain your positional uncertainty within an acceptable value. An autonomous vehicle uses a map containing features that can be used as reference points and triangulate its position based on that. A human brain does this constantly using its eyes, ears and memory. It is an example of diversity: you correlate the perceived displacement by your internal ear with what your eyes sees, using a reference learned in your brain about your surroundings and sensors' ability.

To reach 1E-9, we cannot rely on such self-learned things: we can agree that the probability for the landscape to change is quite higher than 1E-9. In the case of trains, driverless trains use coded beacons / loops or GPS diversity. Such techniques imply that the infrastructure around your vehicle collaborates to the safety of the system. Hence my statement.

This being said, the rail industry has been dreaming for long of a completely vehicle centric solution. There are high stakes for that: reduced costs, competitive advantage, etc. Last attempt here: http://www.alstom.com/products-services/product-catalogue/ra...