Somehow I knew you were gonna say that! And I actually agree. Bad example and all that.

I can only hope that he was only fooling around for the journalists / photographers and not really driving.

As for why there was a motorcycle on set in the first place... They had very strict time schedule, to film as many scenes possible, as they had to finish at 6 PM exactly. And only half an hour lunch break, but it was far to walk. One day Leonard Nimoy started to go there by bicycle to be first in line. And apparently one day Bill upgraded ;)