John L. Walters and Simon Esterson interviewed Margaret Calvert. Margaret Calvert worked on the sign system for UK’s motorways and roads. It is published in Eye number 107 (volume 27).
Website: https://www.eyemagazine.com/feature/article/reputations-margaret-calvert
Available from: https://eyemagazine.escosubs.co.uk/home.htm
[A 2024 interview on YouTube. Earlier exhibitions about her work were held in 2020 and 2021.]
More background about road signs: Robert Dewar and Monica Pronin wrote about the comprehension and legibility of road signs. (Alas, a paid link.)