# Considering how solids act when they are heated and cooled, why do you think they put flexible connections in the road on a bridge?

For concrete, the expansion amounts to about one part in ${10}^{-} 5$ per °C, which translates into only one centimeter over a distance of a kilometer for each 1°C temperature increase. Even still, room must be given to allow for this, or the roadway would buckle as the temperature rose from (say) -10°C to +30°C, or pull apart as the temperature fell.