A study was undertaken to assess the effect of vehicle heat on bituminous pavement by comparing it with the effect of solar radiation. The catalytic converter (or catalyst) was chosen to represent a vehicle exhaust system. Catalysts transfer heat to pavements primarily by radiation, which can be calculated on the basis of existing theories. Two methods were used to calculate radiation from catalyst to pavement: view factor and solid angle. A simplified experiment showed that view factor calculation was closer to measured heat transfer. Data from catalysts of three vehicles were taken. Solar radiation absorbed by the pavement can be estimated from existing models and meteorological data. Results indicate that for one vehicle, pavement directly under the catalyst with an area the same as or smaller than the catalyst absorbed more radiation from it than from the sun. Size and temperature of the catalyst, distance between catalyst and pavement, and oxidation level of the catalyst material were all important factors. Because of the very small sample of vehicles studied, no general conclusions were drawn about whether vehicles on highways increase pavement surface temperature and cause rutting damage.