Motorway signs, says Calvert, were made sky blue because it was a colour that fitted well in the landscape. Signage on A-roads was picked out in a carefully chosen shade of harmonious green (a compromise between the colour that Kinneir and Calvert wanted and the darker ‘smoking jacket’ green preferred by a Civil Service official). They created two clear sans-serif typefaces, Transport and Motorway, to replace existing fonts which were difficult to read at speed.

Kinneir and Calvert’s innovations also included a branched line to denote junction layouts from the driver’s point of view and keeping information to the bare minimum. Calvert was specifically in charge of the human and animal images, and came up with a now iconic set of deceptively simple black pictograms on white backgrounds for hazards such as ‘farm animals’ and ‘school crossing’. The picture on the latter of a girl leading a small boy by the hand replaced an older one where a boy was leading a girl. Calvert later disclosed that the girl in the new sign was based on a photo of herself as a child.

In 1964, Calvert became a partner in the practice. Over the next 20 years, Kinneir Calvert Associates created designs for institutions including British Rail, the NHS, BAA and the army. Calvert created an eponymous typeface, ‘Calvert’, and took up teaching the next generation: she was head of graphic design at the Royal College of Art until 1991. Dubbed ‘a house style for Britain’, the innovative designs she helped to create changed the face of the country forever.

The Forgotten Women series is part of Stylist’s Visible Women campaign, dedicated to raising the profiles of brilliant women past and present. Find out more about the campaign here, and see more Visible Women stories here.

The innovative woman artist who created every UK road sign