Start with where your customers already spend time. For a restaurant that might be nearby offices at lunch. For a home services company it might be residential streets in the evening. For an event it is the venue and the roads leading to it. A good route connects those places rather than covering as many miles as possible.
Then choose the hours. Traffic volume matters, but so does attention: slow-moving traffic, busy sidewalks, and parking lots near popular destinations give people more time to read your ad than an empty highway at speed.
Campaign length depends on the goal. A grand opening or a single event can work with one or two days of focused coverage. Building name recognition in a new area usually takes repeated exposure, so a weekly route over several weeks tends to work better than one long day.
Finally, decide how you will measure it. A dedicated phone number, a promo code, or a simple question at checkout about where customers heard of you makes it much easier to judge a campaign against the recap of dates, hours, and areas covered.