A local authority has various powers relating to the highway, the majority of which are contained in the Highways Act 1980 (HiA 1980). These powers extend to interventions where land adjoining a street (defined as a result of HiA 1980, s 329 by virtue of section 48 of the New Roads and Street Works Act 1991 as any highway, road, lane, footway, alley or passage, any square or court, and any land laid out as a way, whether or not it is formed as a way, a bridge or a tunnel) poses a danger or annoyance, pursuant to HiA 1980, s 167. HiA 1980, s 167(9) provides that 'retaining wall' means a wall, not forming part of a permanent building, which serves, or is intended to serve, as a support for earth or other material on one side only. HiA