Your municipality, realtor or county can usually provide traffic counts (vehicle and pedestrian).
Counting traffic in person at your potential site may give you valuable insight that simple data does not provide. Such as types of vehicles, busy/slow traffic patterns, likelihood the traffic may turn into potential customers, how fast does the traffic flow past your sign, etc. You might think it beneath your status to count traffic, but are you prepared to risk your investment on someone else's data? Do your own due diligence, and get intimately familiar with your potential site and business.