Promoting Craft Fairs

Im trying to improve the promotion of my local fair. I currently distribute posters, flyers, advertise on local radio, and use Social Media - all very successful. Traders have suggested I put a banner on the A1 near to the location of the fair.
Does anyone use banners on major trunk roads to promote their Craft Fair? Do you need permission? If you do, who from - the local Council, Police or other? Any other suggestions welcomed.
Thanks to other bloggers for any assistance on this one!