Frank Blackmore: Traffic engineer who invented the mini-roundabout

Frank Blackmore's invention of the mini-roundabout had a profound effect on traffic engineering. During the 1950s and 1960s traffic growth exposed the weaknesses of earlier roundabout designs, which operated without any priority rule, and allowed entering traffic to force its way unchecked into the junction. This caused jams sometimes so fierce they could only be unlocked by traffic police. Designers responded by building ever-larger junctions in an attempt – largely unsuccessful – to absorb traffic surges without locking. The result was increasing intrusion, land-take and cost.

Blackmore's work changed this in two radical stages. Firstly he successfully advocated an "off-side priority" rule, requiring entering traffic to give way to traffic to its right on the roundabout. Secondly, he then went on to exploit this to create far smaller designs, right down to a painted disc on the road – the celebrated mini-roundabout. All of these designs, particularly minis, were less intrusive, much cheaper, and they significantly reduced congestion and accidents.

These advances did not come easily. Blackmore pioneered the work through the 1960s and 1970s against the marked resistance of a very cautious profession. But he was unstoppable. He combined charm and fluency of conviction and used the results of his own extensive experimentation to persuade, cajole and convince a growing band of enthusiasts among local authority and government engineers. His designs were ultimately incorporated in government manuals in 1975. The results are nowadays so ubiquitous that it is easy to forget just how radical his approach was.

Frank Blackmore was born in colonial Algeria in 1916, at a town then known as Fort National, of a Swiss-French mother, Clarisse, and British missionary father, Josiah. He studied engineering at Lausanne University, Switzerland, and then moved to the UK to work in Colchester's borough engineering department. In 1939 he joined the RAF as a pilot, flying Wellingtons. He once told me of a forced landing he had had to make off the west coast of Scotland, on a beach where there was nothing but, extraordinarily, a working red telephone box, and so remote that he and his crew had to be rescued by sea. He remained in the RAF until 1959, working first for the Air Ministry in London, then for Nato in France, and finally as Air Attaché at the Beirut embassy.

He joined the Transport and Road Research Laboratory in 1960 (now the Transport Research Laboratory) and it was there that his ground-breaking work was done. Although his primary focus was in the UK at that time, he also devised successful junction experiments in places as diverse as Bangkok and Baghdad.

His approach never lacked scale – with his team he conducted large experiments on the test track and public roads, including some designs so radical they proved too much for local engineers. Two surviving exceptions are the "ring-junctions" (also known as the "magic roundabouts") at Hemel Hempstead and Swindon, where Blackmore converted existing very large roundabouts into a ring of two-way connecting roads between satellite mini-roundabouts. The public road experiments were daunting. Overnight, and with police oversight, Blackmore and his team would clear the existing junction – in some cases hundreds of metres across – and change the whole layout completely. If it was not all done by the following morning's rush-hour, and occasionally it was not, chaos awaited the unsuspecting motorists.

In 1975 he won the Wolfe Award for his work on roundabouts, and in 1976 he was appointed OBE. Although formally retiring in 1980, he went on to work as consultant in France and Switzerland. He played a key part in persuading French engineers to give up their old "near-side priority" rule – so perverse to roundabout operation under traffic load – and replace it with his off-side priority rule. His work is currently being enthusiastically promoted in parts of the United States.

Frank Blackmore was above all a generous man, whose determination to succeed was always tempered with great personal kindness.

Rod Kimber

Frank Cuendet Blackmore, traffic engineer: born Fort National, Algeria 16 February 1916; DFC 1944; OBE 1976; married 1939 Ginon Dufour (died 1942), 1945 Eva Johnson (one son, two daughters; marriage dissolved 1969); died London 5 June 2008.