What are the origins of the clearance heights stated on this webpage?
The height clearances over footpaths and cycleways are specified in the County Council’s Highway Safety Policy . See 1.21 and 1.22 in Appendix 1 of the Highway Safety Policy vers 6.1 effective 1st January 2021 – Roads and transport (devon.gov.uk)
The Policy does not specify a dimension for vertical clearance over the carriageway for obstructing trees or overgrown hedges or bushes. But states “the minimum vertical clearance over the carriageway needs to take account of the traffic using the route”
The Policy does specify in 1.3 Obstructions in Appendix 1 for carriageways “The minimum vertical clearance to permissible overhead signs/ banners or cables is 5.03m”.
National advice on required headroom to structures is contained within the Design Manual for Road and Bridges, CD143 and CD195 on the Standards For Highways
National advice on required clearance and mounting heights for signs is contained within the Traffic Signs Manual, Chapter 1
The guidance for landowners provided on the County Council’s website is based on the Highway Safety Policy and this national advice, with an allowance for seasonal growth.