It's probably on a part in the shade? I have the same problem on a shaded patio area at the bottom of my garden. I tried expensive moss killers, it came back. I now use bleach, the cheap non-thick stuff that costs about 29p for 2 ltrs. Dilute it about 3:1, use a stiff yard brush to work it in and hose it down the next day. I have also aplied it to small areas in between patio stones using a garden sprayer. Im not too sure if bleach might cause tarmac to lighten or damage it though. Try a small patch first. I have also heard that boiling water, soap powder diluted in hot water or vinegar are supposed to work, but I've not tried them.

I've used a product called Armillatox. It smelt just like Jeyes Fluid and the smell hung around for weeks. You have to avoid run-off onto plants you want to keep and the moss still needs to be brushed off with a stiff broom. There are no labour free answers to this one, I'm afraid.