  One of the most impressive applications of a quantum annealer was optimizing
a group of Volkswagen to reduce traffic congestion using a D-Wave system. A
simple formulation of a quadratic term was proposed to reduce traffic
congestion. This quadratic term was useful for determining the shortest routes
among several candidates. The original formulation produced decreases in the
total lengths of car tours and traffic congestion. In this study, we
reformulated the cost function with the sole focus on reducing traffic
congestion. We then found a unique cost function for expressing the quadratic
function with a dead zone and an inequality constraint.
