Self-driving Citroën DS: Britain’s 1960s pioneer

By Ryan Standen

| 7 Jul 2025

Classic & Sports Car – Self-driving Citroën DS: Britain’s 1960s pioneer

One day in 1961, a scientist from the Road Research Laboratory was flicking through a newspaper.

Perhaps they were reading about John F Kennedy’s presidential inauguration, the construction of the Berlin Wall or Ham, the chimpanzee that went into space.

They briefly looked up from the broadsheet to make sure all was well with the Citroën DS19 in which they were travelling.

The steering was a little jerky, but otherwise, the self-driving Déesse was working great.

Catching up on the headlines while the self-steering Citroën DS navigates the Road Research Laboratory’s course

They returned to the paper and thumbed through the sports pages.

Fellow researchers watched on as their creation steered itself around the RRL’s 2.5-mile test track in Crowthorne, Berkshire.

The next step? The open road. And the newly constructed M4 motorway would provide the perfect proving ground.

The Citroën DS19’s computer sits on the back seat

Modern autonomous cars are crammed with technology: cameras, radar and GPS work together to feed algorithms the data they need to understand what’s going on around them.

Most of this equipment wasn’t available to RRL scientists in the late ’50s, when ideas for a self-driving vehicle began brewing.

Early trials, carried out in 1959, focused on making driving safer in poor weather.

Within a year or two, the researchers got their hands on a 1960 Citroën DS19, registered YXU 845, and transformed it into a testbed for their new ideas.

The Citroën DS19’s 'chip-cone' roof-top indicators; from the outside, the Road Research Laboratory’s rolling testbed looks standard

This French saloon car had been revealed a few years earlier, at the 1955 Paris Salon.

Customers were impressed by its ‘magic carpet’ ride, if not all that interested in how it actually functioned.

Back in Berkshire, the Citroën’s inner workings sparked the curiosity of the RRL boffins.

“They chose the Citroën DS because of its innovative hydraulic systems,” says Heather Bennett, associate curator at the Science Museum in London.

The Citroën DS19’s actuated steering wheel appears normal

The car’s suspension, brakes, power steering, clutch and gearchange were all pressurised by an engine-driven pump.

As a result, the Citroën DS19 was much easier to automate than other vehicles, whose main controls were operated by multiple, independent systems.

“The RRL was looking into automation for driving on motorways and trunk roads,” explains Heather.

“They envisioned a human would still be in control for driving in towns and on minor roads.”

Road Research Laboratory scientists didn’t perfect lane-changing, so wing mirrors remained

In the early ’60s, a cable was buried beneath the RRL’s proving ground and charged with current at a frequency of 5kHz.

At first, the team added a warning light that alerted drivers when they strayed too far from the cable, with driving in thick fog in mind.

Things ramped up when the DS19 was fitted with sensor coils and a servo valve to control the steering, so the modified Citroën could track the cable’s electromagnetic field with no human input.

The Citroën DS19 might look a bit Jules Verne today, but this was cutting-edge stuff in the 1960s

From the outside, YXU 845 looked ordinary: no military-grade radars, bolted-on trackers or Knight Rider-esque LED strip on the nose.

Peer inside, though, and you’d notice that one of the rear seats had been commandeered by the control centre and instrument panel for the Citroën’s electronic systems.

Here, the self-steering DS19’s brain gathered information from sensor coils – attached to the front of the car – then fed instructions to the steering servo via electrical pick-ups that measured the angle of the front wheels.

The red button above the Citroën’s dashboard is marked manual override, and the driver could always take back control of the steering wheel

Engineer KHF Cardew explained the Citroën’s technology in a report published in 1970: ‘The position of the magnetic field was sensed by equipment in the test car.

‘This generated a lateral position error signal which fed into an electro-hydraulic servo system operating the steering and enabled the vehicle to follow the buried cable.’

In summary, Heather says: “It’s a more sophisticated version of running on a rail. It’s not physically fixed to something, but it’s very much following and responding to the input from the cable.”

The electro-hydraulic servo valves were a wartime invention designed to control the flow of hydraulic fluid to an actuator (in this case, a device which converts fluid pressure into movement).

Later Citroën DS models were fitted with directional lights, but this DS19 packs even more exciting technology

Early EHSVs were slow and inaccurate, but the technology was more refined by the 1950s.

Throughout the ’60s, the RRL continued to update and upgrade YXU 845.

Initially, improvements involved fine-tuning the EHSVs to smooth out sharp steering inputs.

The team found the car was ‘hunting’ over the cable (moving from side to side in a simple harmonic motion), so stabilising circuits and a lateral accelerometer were integrated to help regulate the vehicle’s behaviour.

An autographic chart recorder, which scribbles data on paper graphs, was installed.

The self-steering Citroën DS19 was put through its paces in all conditions

Results showed that the DS19 was much more stable in a straight line with the accelerometer fitted, but it tended to stray further from the underground cable in corners – sometimes by up to 50mm more than in experiments without it.

Results were largely positive, though. The bravest scientists and engineers accelerated up to 80mph on the Crowthorne track, depressed the pedal that engaged YXU 845’s self-steering system and handed over control to the onboard computer.

Researchers even evaluated the Citroën in the snow, at 60mph.

In a straight line, the car stayed within 20mm of the underground cable, but it drifted by up to 130mm in corners.

The Citroën DS19’s hydraulic systems made it ideal for self-driving tests

Engineers reckoned that they could have gone faster, but 80mph was all the loaded-up Citroën could muster.

The DS19’s tendency to understeer was also an issue.

Cardew concluded: ‘It is not possible for the vehicle to negotiate a curve without displacement from the cable, and the greater the forward speed the greater the displacement.’

As the M4 motorway took shape between 1961-’71, the team jumped at the opportunity to study YXU 845 on a real road.

‘The bravest engineers accelerated up to 80mph on the test track and handed over control to the on-board computer’

A nine-mile cable, similar to the one embedded in the Crowthorne facility, was installed beneath a stretch between Reading and Slough.

Trials were abandoned when the M4 opened to the public in the mid-’60s, but the cable remains to this day.

Across the Atlantic, a team in the USA was also toying with the idea of autonomous cars: the 1964 GM Firebird IV, a rolling concept created for that year’s New York World’s Fair, envisioned a future in which vehicles would travel on ‘electric highways’.

Unlike the RRL’s Citroën, GM’s jet-age four-seater was a flight of fancy rather than a practical test rig.

Sensor coils process inputs, then that data is used to calculate an appropriate servo valve output

Back in Berkshire, the technology looked promising and some believed that it could be commonplace by the 2000s.

“Researchers estimated it could reduce motorway accidents by up to 40%,” says Heather.

“They also thought it might help to make driving more accessible for those with disabilities. It would be a good model for public transport, too.”

What’s more, motorways could be made more efficient by narrowing existing lanes and adding new ones, while vehicles automatically maintained safe stopping distances.

It was found that, in many instances, the self-steering Citroën’s reaction times were quicker than a human’s.

YXU 845 was based on a standard Citroën DS19; apparently Road Research Laboratory staff liked to get their hands on the latest cars

The solution was far from perfect. The car still lurched from side to side, it needed to be assessed on tighter bends, there was no way to prevent a head-on collision on a two-way road, and a system of changing lanes would have to be devised, but it set the ball rolling.

“It was automatic rather than intelligent,” Heather says. “Today’s automation works in a different way.

“The focus is now on inner-city and urban driving, which requires the vehicle to make decisions in response to external stimuli, such as pedestrians crossing the road.

“The RRL team’s work was divided into two categories: lateral, which was the steering, and longitudinal, for speed and stopping distances.” Apparently, the former was much easier to automate.

The self-steering Citroën DS19 automatically followed a buried cable, but the driver could always grab the wheel to regain control

By 1969, RRL scientists were experimenting with ways to control the Citroën’s speed relative to other road users.

A 1969 report said: ‘The longitudinal law will be tested using a taut wire ‘yo-yo’ device to supply range and closing speed measurements to the control computer.

‘The difference between the output of this computer (ie, the vehicle’s required acceleration) and the measured actual acceleration will be used to control the brakes and throttle.’

Alongside these trials, the RRL was also working with the Royal Radar Establishment in Malvern to ‘decide whether lasers, radar, ultrasonics, or some other method’ could be used.

The Citroën’s modified engine bay includes rubber steering-control cords and a force-correction pulley, mounted behind the numberplate

In a few years, the RRL’s work progressed from a rudimentary version of today’s lane-keeping assistance to a concept that sounds like a precursor to the autonomous technologies that Tesla, Google, Waymo and others tried to crack five decades later.

It appears that the researchers knew they were on to something, too, because rather than scrap the Citroën or repurpose it for another project, it was donated to the Science Museum in 1973.

“We have a few other items from them,” says Heather, “mainly measuring equipment from different tests.”

But why get rid of YXU 845? “It was to do with funding,” she says. “They proved the system was effective with one car, but being able to scale it up and ensure it was reliable and safe would be very costly; putting the infrastructure in place would be even more. I think it just wasn’t a priority at the time.”

The Road Research Laboratory’s Citroën DS was a self-driving car built in Britain a decade before Elon Musk was born

Similar projects continued in the ’70s with a modified Ford Cortina and a Mini, but progress petered out as the RRL focused on other projects (see below).

Perhaps the road to automation was not as straightforward as it first seemed?

Public acceptance, legislation and moral conundrums about the decisions a car should be allowed to make are some of the barriers facing self-driving technology companies today.

The RRL, now the Transport Research Laboratory, didn’t return to self-driving vehicle trials until its GATEway Project in 2015, when four autonomous pods were let loose in the capital.

“They proved the system was effective with one car, but being able to scale it up and ensure it was reliable and safe would be very costly”

Are we asking too much of the tech? Maybe they don’t need to be in control 100% of the time.

The mind-boggling algorithms and game-changing Lidar sensors are impressive, but, in our quest for automation, perhaps we have overlooked the relatively simple solution developed by the RRL in the 1960s.

Either way, Silicon Valley rules the roost when it comes to self-driving technology in the 21st century, but it’s nice to know that much of the groundwork was laid by a team of scientists and engineers in Berkshire, England, some 60 years ago.

Images: Science Museum/Transport Research Laboratory

Thanks to: Science Museum; Transport Research Laboratory; Hannah Fry’s book, Hello World (ISBN 9780857525246)

More Road Research Laboratory experiments

Cars were once tested at up to 155mph on the banked circuit. Today, pedestrian traffic passes at a more sedate pace

The Road Research Laboratory was established in 1933, when the Department of Scientific and Industrial Research took over from the Road Experimental Station in Harmondsworth, London.

Initially, its main job was to advise the government on what materials and methods to use for its rapidly expanding network of highways.

After helping the Ministry of Aircraft Production and other departments during WW2 (investigating methods to speed up the construction of runways and testing the bouncing bomb for the Dambusters raid were among its wartime jobs), it was given the responsibility to study other areas of road safety in the 1940s and ’50s.

In 1966, the RRL moved its headquarters to the Crowthorne proving ground in Berkshire.

The fire tower doubled as a vantage point for experiments on The Pan

It conducted a huge variety of trials, from experiments with early sat-navs to creating an inhibitor that could be added to road de-icing salts to reduce vehicle corrosion.

The latter involved ordering a batch of seven ADO16 saloons from BMC and then driving them through shallow pools of water.

Some cars were driven into a pool of rainwater, others went through salty water, and the rest forded salted water mixed with the new inhibitor.

When signs of corrosion began to show, the cars were cut open and assessed.

Road Research Laboratory trials included this heated road, which was installed in Slough

The RRL helped pioneer vehicle safety innovations throughout the 20th century, analysing rear-view mirrors, anti-lock brakes, deformable front bumpers and more.

“Take your pick,” says Penny While, head of marketing and unofficial archivist at the Transport Research Laboratory (as the organisation was renamed when it became an executive agency of the Department of Transport in 1992, shortly before it was privatised in ’96).

“The TRL takes other people’s ideas and road tests them to find out if they are viable and helpful.

“Seatbelts were not an RRL invention, but it led the way in devising the test standards for their use and persuaded car makers to adopt the three-point system.

“Anything that helps keep the traffic flowing smoothly and safely, and reduces maintenance costs, is up for investigation.”

The Road Research Laboratory’s work led to the ‘give way to traffic from right’ rule when joining a roundabout

“The RRL also co-developed crash-test dummies when it became unethical to use cadavers,” she continues.

“Some of the stranger things the lab has tested include heated roads, electric snowploughs and asphalt made of recycled water bottles.”

It also created what became the European New Car Assessment Programme (Euro NCAP).

Today, the TRL still has its headquarters in Crowthorne, but it gave up the adjacent test facility in 2015.

Some of the old site has been used to build new houses, but part of it remains as Buckler’s Forest, a nature reserve that’s open to the public.

The Small Roads Test Track replicated urban routes

Wandering around the area, you can still find traces of the RRL’s projects.

The huge fire tower – now a home for birds and bats – is perhaps the most obvious; it once overlooked some of the large-scale trials conducted on The Pan.

In 1967, thousands of cones were laid out to create a makeshift road network on the concrete expanse.

Nearly 200 vehicles were involved in the test to find out how traffic lights impacted traffic jams.

Drivers were paid five shillings an hour to take part.

The Transport Research Laboratory’s Buckler’s Forest test facility closed in 2015

From the tower, you can follow the same track where the self-steering Citroën DS proved its mettle in the ’60s, before arriving at the banked curve that’s now being reclaimed by nature.

From there, you can venture deeper into the pine trees to find the Small Roads Test Track.

Designed to resemble side streets and urban areas, there’s a cluster of road markings, traffic signs, cat’s-eye reflectors and more.

The RRL wasn’t just concerned about a vehicle’s occupants: it investigated pedestrian safety, too.

In the late 1940s, it was tasked with finding the best way to make road crossings safer and more visible.

Hill Start Hill – now a picnic spot at Buckler’s Forest nature reserve

The researchers trialled various markings, but the black-and-white zebra pattern performed best.

Little surprise that the UK’s first-ever zebra crossing appeared in 1951 on Slough High Street, not too far from the RRL’s base.

Heading back towards The Pan, you can take a rest on Hill Start Hill.

The 1-in-6 gradient slope used to be a challenge for vehicle handbrakes, but now it’s a great picnic spot for when you’ve finished the 2.2-mile walk around Buckler’s Forest.

Images: Chris Gage/Transport Research Laboratory

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