Could you elaborate? What's a booze bus? In the US, It's a pretty common occurrence to see someone pulled over and breathalyzed if they're driving erratically.
A booze bus is a random breath test - the police have labelled busses that they park on the road. I believe if you blow over the limit then you get on the bus and are tested again in 30 minutes.
They look like this: http://www.ranted.com.au/wp-content/uploads/2012/09/109890-b...