Yes, you can. If the security guard stops you, just take out your camera and start filming and then ask him again, that is a public road and he must let you pass!
The other side of the tunnel actually emerges from Citibank Plaza, and you can either :
(i) drive downwards via Garden Road and route towards Admiralty via the fly-over on the left
or
(ii) drive upwards via Cotton Tree Drive and use Kennedy Road towards WanChai.
