Roundabouts:
Taming the streets

Many of the first roundabouts engineered for controlling traffic were crude affairs. Yes, they had a central island and road traffic had to go around it, but to begin with, the slow-moving (often horse-drawn) traffic of the early twentieth century could travel around the roundabout however it wished, with no rules governing direction of travel or priority.

Before roundabouts could become a a serious method of traffic control, rather than just a pleasant-looking focal point amid swirling traffic chaos, they needed to be controlled properly.

Turn left! It's how all roundabouts work.

Turn left! It's how all roundabouts work.

Grinding to a halt

In the beginning, there were no rules and roundabouts were a free-for-all. The convention of travelling clockwise around them (or anticlockwise in right-hand-drive countries) arrived relatively quickly: if traffic always kept to the left side of the road, it made sense for it to pass around the left side of the traffic island. By the 1920s this was an established convention.

Left, left, left please
Left, left, left please

For decades, however, courtesy existed in place of priority. Traffic joining the roundabout squeezed in wherever it could and vehicles already circulating tried to make way for it. The junctions were slow to pass around because at every entry point, everybody had to slow down and work out what the other motorists around them were doing.

Rules were obviously needed, and in some places they were introduced. The north-eastern USA - in particular the states of New Jersey and Massachusetts - had a growing number of rotaries. A rotary junction is much like a roundabout, except that it's much larger and often it's the traffic joining that takes priority. Lanes will enter and exit at various points, leading to many lane-changing maneouvres within the junction. The Arc de Triomphe in Paris is a rare example of an European rotary junction.

The trouble with rotaries was that they would lock up very quickly under heavy traffic: with more vehicles piling on at every entry point, and traffic constantly fighting for space to change lanes, they would fill up until nobody could reach their exit and the junction became completely clogged.

Partly as a result of its painful experiences with rotaries, and partly because of some research that modelled roundabouts as successive weaving movements on isolated parts of the junction rather than as a single, whole entity - American highway engineers largely wrote off the roundabout in the 1960s as an irrelevence.

Absolute priority

Needless to say, Britain went in the other direction completely, following the lead of a few roundabout-sceptical countries like Germany and Ceylon, and dabbling with the idea of restricting the flow of traffic on to the roundabout. The idea was really quite simple: make traffic wait to join, then give it absolute priority until it leaves, and you stop the junction locking up - because nobody can block the path of vehicles trying to reach their exit.

RRL priority rule experiment in Middlesbrough, 1958. Click to enlarge

RRL priority rule experiment in Middlesbrough, 1958. Click to enlarge

The first tentative experiments included one in Middlesbrough in October 1958, at a roundabout (now vanished underneath an embankment for the A66) at the junction of the A176 Stockton Road and the A1130 Newport Bridge Approach. The Road Research Laboratory made one change to the existing roundabout, which was to add signs on each approaching road stating "GIVE WAY TO TRAFFIC FROM YOUR RIGHT".

Give Way sign from the early 1960s. Click to enlarge
Give Way sign from the early 1960s. Click to enlarge

The results were excellent, with much of the peak time congestion evaporating as soon as motorists began observing the new rule. (The RRL noted with some dismay that the problem was not completely fixed, as during the rush hour some approaches experienced delays of up to one minute. Sounds like paradise to me.) With incredible speed, designs were drawn up for new road signs to introduce the priority rule on roundabouts all over the country (shown left; click to enlarge), and the Ministry of Transport was inundated with requests for approval to use them.

The effect was enormous, given the minor change that had been made. Where previously a roundabout had introduced some orderliness to a junction, it now had the power to dramatically increase its capacity, and as part of that, reduce delays to everyone using it.

Countries that adopted the priority rule have seen roundabouts flourish as a modern and valuable tool in assisting the flow of traffic, France being the key example. Those that didn't adopt the system saw the roundabout fall out of favour - and even today you'll find very few roundabouts anywhere in the USA. It's only very recently that they have made a return there, always with the priority rule in place.

Spreading around

The introduction of the priority rule couldn't have come at a more appropriate time. It turned the humble roundabout into something capable of handling large volumes of traffic efficiently. Unlike normal priority junctions, it gave equal priority to everyone, avoiding uneven waiting times on different approaches to the junction. Unlike traffic signals, it didn't force anyone to wait or to go, and let motorists choose their movements so they were only kept waiting for the shortest possible time. And unlike unruly urban junctions of the time, it didn't require a police officer to regulate it.

An urban roundabout, dating from the early 1960s, in the London Borough of Southwark

An urban roundabout, dating from the early 1960s, in the London Borough of Southwark

The Tulse Hill Gyratory. Click to enlarge
The Tulse Hill Gyratory. Click to enlarge

All of this was exactly what the town planners and highway engineers of the 1960s were looking for. The design philosophy of the time was geared towards free, unfettered movement of motor traffic and - in the glorious, uncongested, choose-your-own-destiny utopia they were setting out to create - the roundabout was the perfect traffic control device.

The explosion in vehicle numbers, and corresponding traffic problems, would eventually be solved with a massive programme of urban road building, according to the Government of the day. In the meantime, local authorities were instructed to facilitate the movement of traffic through more efficient use of what was already there: one-way systems, parking regulations, and - it goes without saying - appropriating circuits of existing streets into gyratory systems and makeshift roundabouts (including the Tulse Hill gyratory, shown right). That urban road boom never happened, of course; it was killed off by a tide of public opposition and the oil crisis. Most of the stopgap roundabouts and gyratories we got in the sixties are still with us today.

Beyond the congested city streets, the planning philosophy of the time was plain to see in the designs and layouts proposed for the many New Towns that were being built. From Harlow to Cumbernauld, from Redditch to Washington, from Skelmersdale to Crawley, they all have one design component in common: roundabouts everywhere. Britain was on the road to becoming a roundabout nation.

Picture credits

  • Photograph of experimental signs in Middlesbrough extracted from National Archives file DSIR 12/257.