Any suggestions on getting a horse used to traffic?

My horse is only young and lizards and kangaroo's still spook him :) But he has a real issue with cars which is completely normal but I'm after some other people's idea's on how they go about desensitizing their horses. Currently he is quite capable of lunging and being ridden in a small yard whilst the chainsaw is a few metres away and I've been hand walking him around the block... quite a large block :) and coming across cars traveling up to 80km but I have him in off the road well away from danger and he still spooks. Aside from that to minimize risk and to maximize the amount of cars we come across... I have someone drive around and around the block for us so they know what to expect and aren't going flat out. What else would you do? My main problem is I dont get to do it enough due to other commitments and getting someone to drive around for me is not always an option. Do you agree that doing this atleast twice a week would still be beneficial although I'd love to have the time to go daily it's just not possible.