Road traffic flows on a straight road segment such as bridges are modelled in this article. The mathematical model of traffic flows has been constructed by using the method of lumped parameters. Changeable lane direction and road pricing has been theoretically investigated in order to understand the shifting in supply and/or demand curves of traffic participants in equilibrium. The article presents assumptions for constructing the mathematical model. Demand can be influenced by road pricing, in its turn, supply can be influenced by extension of infrastructure with reversible lanes.