UL 4600 is initially aimed at fully-autonomous operation of passenger vehicles within a restricted operational design domain (SAE Level 4). It is planned that a subsequent version of the standard will include other autonomous systems such as factory warehouse robots. The standard permits human operation of vehicles. However, safety during human supervision and human operation of vehicles are excluded from its scope.
Is this a standard for how to test autonomous vehicles on public roads safely?
No. This standard is focused on building a safety case for the deployment of SAE Level 4/5 vehicles, not for practices related to on-road testing. The practices involved are sufficiently different that a separate standard is required for on-road testing safety.