Hence off-peak fares heavy rail fares undercutting bus fares and fares on such as Metrolink undercutting buses when the journey doesn't involve entering the regional centre.
Although this is an anomaly generally restricted to metropolitan areas in Britain. In most major cities, transport is usually run by one municipal operator, or run by private companies contracted to a public authority, so there is no reason for one mode to undercut another, especially as their networks are usually integrated. National rail fares are sometimes also included within the standard city fare structure where they play a significant part in the city transport network.