A straightforward method is shown for calculating thermal stresses in bridges. Unsteady temperature distributions are obtained from numerical solutions of the one-dimensional unsteady heat equation, and comparison with experiment seems to validate the simplifying assumption that horizontal heat movements are small enough to be ignored. Stresses are calculated by solving a two-dimensional thermoelastic problem, and a design example shows that stresses calculated in this way can be significantly larger than stresses calculated by ignoring the coupling effect between longitudinal and lateral stresses.