Interesting

"The cars are to drive alongside commuters, but in public testing a driver is always to be present, as Victorian law requires drivers always keep a hand on the steering wheel. However, in occasional closures of the Burnley Tunnel, with no other drivers to endanger, the cars are to be tested with nobody in the vehicle."

I'm wondering how laws are treated in the latter case? Has an official exemption been given?

I expect such autonomous cars to work well at a highway (probably) but not at smaller roads where the situations are more unusual and exotic.

I'd guess the wording of the law limits when it applies — for example, it might say to keep hold of the wheel "when driving on a public way", and they decided driving in a closed tunnel with nobody there wouldn't be public.