393.Section 271 makes TfL the traffic authority for GLA roads. For roads in Greater London that are not GLA roads or trunk roads, the traffic authority is the relevant London borough or the Common Council.
394.Section 272 creates a new class of road called “GLA side roads”, for which TfL will also be the traffic authority, but not the highway authority. It inserts a new section 124A into the RTRA 1984 (RTRA 1984) to provide for the Secretary of State to designate roads which are to be GLA side roads (in the same way that section 227 provides for him to designate the first GLA road network). Sections 14B and 14C of the Highways Act 1980 (inserted by sections 258 and 259 of this Act) which enable the Mayor to change and keep records of the GLA road network, can be applied to GLA side roads by order of the Secretary of State.
395.Section 273 provides for TfL to place traffic signs on nearby roads (for which the relevant London borough council is the traffic authority) in connection with a GLA road. The signs may be placed on any structure on that road, whether or not the structure belongs to TfL. TfL may carry this out in connection with traffic regulation and experimental traffic orders and in other circumstances (e.g. temporary traffic orders under section 14 of the RTRA 1984), provided they consult the London Borough Council which is the traffic authority for the road. (Experimental traffic orders are used where the effects of the order cannot be confidently predicted. They also provide for the fine-tuning of the measures without the need to amend the order and for its effect to be monitored before decisions are taken on whether or not to make it permanent.)  Section 274 extends to TfL the powers of a London borough council to affix traffic signs to walls.
396.These sections also provide that responsibility for maintaining, altering or removing traffic signs rests with the traffic authority responsible for the order which enabled the placing of those signs. They further provide that where the sign is on or near a GLA road, or is erected as described above, TfL will be the traffic authority for that sign.
397.Where TfL exercises its powers in relation to traffic signs otherwise than in connection with a traffic regulation order or an experimental traffic order, it can remove or reposition those signs whether or not  they were placed by TfL. Where TfL removes or repositions a sign placed by another authority, that sign will vest in TfL. The traffic authority for the road where the sign has been placed or repositioned by TfL cannot alter or remove the sign except with the consent of TfL or by direction of the Secretary of State.
Commentary on Sections Part Iv: Transport Chapter Xiv: Road Traffic Sections 271 to 274: Transport for London as a traffic authority