Somewhere between the Columbia River, a line of interstate traffic and consumers’ wallets lies a sweet spot, and David Pietka thinks he’s found it.It’s inside a running shoe.“An 8 percent tax on $100 is $8. The decision for everybody,” said Pietka, “is what’s their break point on a price of a good before they travel to Portland?“We are expecting that it will be closer to our price and the Vancouver people will appreciate our support of their community and will stay here in Vancouver and buy these products at this price point.”Pietka is co-owner of Foot Traffic, a running shoe and supply retailer with four locations in Portland. At 10 a.m. Saturday, a fifth location will be added, at 305 S.E. Chkalov Dr. in east Vancouver. Foot Traffic will be trampling the conventional wisdom that the typical Southwest Washington consumer would prefer to cross the bridges for sales-tax-free purchases in Oregon. But Pietka and the other co-owner, Sean Rivers, think the combination of location, competitive prices and customer loyalty will win the day. On top of that, there may be a civic-minded component.The Foot Traffic co-owners had been considering a move to Vancouver for some time, Pietka said. Possible locations included the Salmon Creek area and 192nd Street corridor as well as the winning location, at Cascade Park Plaza, chosen because of its proximity to the entire community, he said.