... no driver of a vehicle shall overtake a vehicle other than a two-wheeled cycle, a two-wheeled moped or a two-wheeled motor cycle without side-car: ... immediately before or on a level-crossing not equipped with gates or half-gates, provided however that Contracting Parties or sub-divisions thereof shall be free to permit such overtaking at a level-crossing where road traffic is regulated by traffic light signals incorporating a positive signal authorizing vehicles to proceed.