Patchett, Nick; Evans, Jeremy: 'London Congestion Charging – a personal account' (Transportation, 2018), 'Road Pricing: Technologies, economics and acceptability', Chap. 13, pp. 337-362, DOI: 10.1049/PBTR008E_ch13
IET Digital Library, https://digital-library.theiet.org/;jsessionid=73028expi9oj.x-iet-live-01content/books/10.1049/pbtr008e_ch13