# Road Vehicles Lighting Regulations (Northern Ireland) 2000, Paragraph 4


(1) A small bus which does not exceed 5500mm in length and does not exceed 2300mm in height shall be fitted with one roof bar.
(2) If a small bus exceeds either of the measurements referred to in paragraph (1) then it should be fitted with two roof bars.

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Source: https://www.legislation.gov.uk/nisr/2000/169/schedule/22D/paragraph/4 (the official version)
Page: https://openlegislation.uk/road-vehicles-lighting-regulations-northern-ireland-2000/schedule-22D/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.