Abstract
The length of a crest vertical curve is governed by visibility considerations. The minimum length is based on the passing sight distance, and overtaking is allowed throughout its length. A theoretical determination is made of the zone of overtaking visibility in a curve designed on a below maximum basis. The conclusion is that, in order to reduce the no-overtaking zone in below maximum cases, it should preferably be as short as possible within the requirement limits of overtaking visibility and driving convenience.