  On highways with two lanes, cars are requested to run on the slow lane and
are allowed to run on the fast lane for overtaking. However, on real two-lane
highways, we daily observe a phenomenon called "reverse lane usage", in which
the flow on the fast lane exceeds that on the slow lane. The origins of the
phenomenon have not been discussed clearly. In this paper, we study a two-lane
extension of the Nagel-Schreckenberg model. We employ two types of
lane-changing rules: a German and a Japanese type. The German type suppresses
overtaking slow cars on the fast lane through the slow lane. The Japanese type,
on the contrary, allows overtaking through both lanes. If two lanes allow the
same maximum speed, the suppression of overtaking through the slow lane is the
key for the reverse lane usage. If the maximum speed on the fast lane is faster
than that on the slow lane, the reverse lane usage is observed in the Japanese
type. The effects of stochasticity in lane changing, and mixing trucks and
passenger cars are also discussed.
