  When we travel by car from one location to another, our route is constrained
by the road network. The resulting network distance is generally longer than
the geodetic distance, i.e. the distance as the crow flies, between the two
locations. We report a systematic relation between the statistical properties
of these two distances. In empirical analyses for large motorway networks in
various countries and areas, we work out distributions of network and geodetic
distances and identify a surprisingly robust scaling property between them. A
simple consequence is that we typically have to drive $1.3\pm0.1$ times longer
than the crow flies. Moreover, we show that this scaling is not present in
standard random networks; rather, it requires a certain non-randomness, namely
adjacency. We develop a set of rules to build a realistic motorway network,
also consistent with the scaling properties found empirically. We hypothesize
that the scaling reflects, in a rather universal fashion, a compromise between
two societal needs: high efficiency and accessibility on the one hand, and
limitation of costs and other burdens on the other.
