The ONE-WAY sign must be used to indicate roads on which traffic is allowed to travel in one direction only. The standard size ONE-WAY sign (Rb-21) should be used on urban streets and/or where the posted speed is 60 km/h or less. For 70 km/h or more use Rb-121. Rb-121 must also be used at the following locations: At freeway ramps in rural areas; At freeway service centers in rural areas; At urban expressways accessed by one-way streets or ramps; or Where the driver environment is complex.