I hate doing tarmac, very easy to leave stripes.
Use a good wide fan nozzel and take your time.  Be very carefull not to cut the tarmac up or rip it up if it is old.  
There is a product on the market from thompsons I think that can be painted onto tarmac after cleaning to bring it back to black.  I have never used it so I cant comment on the quality of it or how good it is.
Good luck with it matey.