For a few years, London had an experimental fleet of buses that dragged a trailer behind them burning a unique type of gas, made from burning coal.

It was wartime and imported liquid fuel was expected to be in short supply, so London’s buses looked to something the UK wasn’t short of at the time, and that was coal. Specifically, London’s buses were powered by the gas that was produced from burning coal — known as producer gas.

In the days before North Sea gas was discovered in the 1960s, most gas supplies in the UK were manufactured by burning coal in a low-oxygen furnace, which incidentally is why cities have old gasometers in them, as the coal gas was usually manufactured in towns close to the point of use in the days before a national grid of gas pipes existed, so had to be stored locally. Hence our cities are littered with historic gasometers.

But back to the buses.

In 1937, at the British International Motor Show, the Minister of Transport, Leslie Hore-Belisha, asked motor companies to investigate alternatives to petrol, and not long afterwards, the Duke of Montrose announced[1] that the Highland Bus Company had carried out successful trials of a bus fueled by coal gas instead of oil-based fuels.

The principle was that a controlled supply of air is passed over a hot carbon bed, and the oxygen in the air unites with the carbon to form carbon dioxide, which is then broken down into carbon monoxide, which can be used to power the bus engines. The main problem is that the energy is considerably less potent than liquid fuels, having a much lower calorific value for the same mass.

Although any carbon-based fuel was usable, such as wood or charcoal, coal was far and away the best (well, the least bad) option for gas producer engines.

The initial trials between Inverness to Dornock used a 32-seater bus with the coal carried on board and was declared to be a success. They then followed this up[2] with a run to London and back. The cost of the coal-based transport worked out much cheaper than imported petrol (that may have been partly due to petrol taxes). The downside was the three refuelling stops and slower journey time. Not much seemed to happen though. A proposal to expand the service to run in Glasgow was made in August 1938[3], “in the interest of national economy”, but the buses were later reported[4] to be sluggish and difficult to drive, and while cheaper to run, were more expensive to maintain[5].

Another trial took place in Plymouth in August 1939[6], with the aim to convert 5 local buses to producer gas as a “war emergency”. The Fuel Research Board issued a tender[7] later that year for companies to start manufacturing producer gas trainers for use behind buses.

The first such bus appeared on London’s streets on the 1st November 1939.

Running on Route 406 between Kingston and Epsom Downs[8], the bus was hooked up to a 10 feet long trailer which carried the fuel generator, which was said to be able to burn anthracite, charcoal or even peat, and the gas was pumped through a hose to the bus engine to power the vehicle.

London’s first producer gas bus was in public service on November 1, for the first time, running between Kingston and Epsom Downs.

The way the engine worked is that gas is produced by burning the coal in the trailer, where it was cooled and filtered, then sucked into the bus engine, where it’s mixed with air and fired by spark-plugs in the same way as a conventional engine works. It was noted that a gas-powered engine could generate only about 60% of the power that a petrol engine could muster up, and this proved to be a problem when going up hills. Going down the hills was not a problem.

Illustrated London News – Saturday 17 February 1940
Image (c) Illustrated London News Group

A trip to show off the bus to journalists took place the following week[9], with a trip through central London and along the Embankment. Although the bus driver confirmed there was a loss of power, the journalists and passengers didn’t seem to notice any problems.

In November 1940, a number of trials were carried out in Nottingham and London with a trailer attached to the back of a double-decker bus.

The Nottingham trial[10] used an engine supplied by Enness-Sentinel, and was supplanted by a petrol engine to get started and for when the producer gas engine wasn’t powerful enough. The Nottingham trial reported that a test run along 9-miles of local roads consumed just 2 pints of petrol

It was expected that a full day would see the bus consume 3.5 gallons of petrol compared to the average of 34 gallons of petrol per day the bus normally needed. However, it wasn’t until 1943[11] that Nottingham saw its first public service fueled by producer gas though.

Back in London…

In early 1942, a fleet of adapted buses based at Grays[12] were converted to producer gas power by the London Passenger Transport Board (LPTB), using different types of gas engines. With lower power outputs, it was less a case of which engine performed the best, than which performed the less badly.

One of the other advantages of producer gas was that, unlike petrol and oil, it was unrationed. Well, until August 1942[13], when the government changed the rules so that all motor vehicles, regardless of the fuel used would be regulated to conserve supplies.

By January 1943 though, it was confirmed[14] that nearly 40 London buses were running on producer gas, and over 200 were doing so across the UK, and by the end of the war, 151 London buses had been converted[15]. By then, 14 bus depots were running buses on coal gas.

To help the drivers get used to these new buses, in February 1944, a booket[16] was produced by London Transport as a small training manual, with a very candid admission about what people thought of the buses.

“You know that oil fuel in large quantities has to be used for the purpose of winning the war quickly, and gas-producer buses are being run not because we like them but because they do enable us to make a substantial contribution towards the great effort in which we are all engaged”

The impact of the buses was significant though, with an estimated saving of 6,000 gallons of petrol for each bus per year. It wasn’t that they could eliminate petrol entirely though, as many of the buses needed to be started with petrol to get them going, while the gas engine warmed up and started producing coal gas.

The staff booklet also warns of how the buses would handle differently and that the drivers need to learn to accommodate the gas producer bus’s unique foibles.

“Fill ‘er up please”

A large number of tests[17] were being carried out by LPTB’s Department of the Chief Mechanical Engineer to look at what could be done to improve the performance of the gas-powered buses, which were noticeably poorer than petrol and oil-based vehicles.

One of the more amusing solutions to keeping the heat sufficient in some of the gas trailers was that the driver should occasionally get out of the bus, go to the back, and poke the fire. A very domestic solution to the problem. There were also issues with keeping the pipes clear of soot, and with the coal hoppers catching fire and needing to be replaced.

Although the buses were considered unsuitable for urban areas, they could be used in the more rural edges of London with longer runs between bus stops and where speed was less important, so long as the geography was amenable – namely not too many hills.

There was also the issue of how much coal would be needed – on average about a ton per bus per week. While it was less of a problem to dig up coal from under the UK than to import oil from overseas during the war, that was still an awful lot of coal to keep London’s buses running.

On the upside, they found coal to be much cheaper, with costs averaging 1.42p per mile, compared to 1.44p per mile for fuel oil and 3p per mile for petrol, but that was offset by higher maintenance costs and the likelihood of needing more buses to cope with their slower speeds.

Producer gas wasn’t limited to buses but was used on small lorries and even some private cars. There was even a trade body set up to lobby for more producer gas vehicles, the Transport Producer Gas Vehicle Makers Association.

In fact, while more widely used outside London, the coal gas-powered buses seemed to be more of an interesting idea driven more by wartime needs than being a practical application that almost, but never quite, managed to get enough traction to become viable.

They faded into obscurity almost as fast as they had arrived. After the war, the trailers were sold off, often to have the generator scrapped and the trailer converted for use behind cars.

But that wasn’t the end of it.

In 1953, gas producer buses were back. Trials were carried out across Surrey and south London, but they came to the same conclusion as before, that while the engines could be made to work, they were hopelessly inefficient.

The days of buses burning coal were over.

But buses burning hydrogen? Now that’s just started.


1] Dundee Courier- Thursday 18 November 1937

2] Aberdeen Press and Journal- – Friday 19 November 1937

3] The Scotsman – Thursday 04 August 1938

4] Dundee Evening Telegraph – Wednesday 18 January 1939

5] Journal of the Royal Society of Arts Vol. 88, No. 4556 (MARCH 15th, 1940), pp. 418-445

6] Western Morning News – -Tuesday 22 August 1939

7] Yorkshire Post and Leeds Intelligencer – Friday 08 December 1939

8] Illustrated London News – Saturday 11 November 1939

9] Aberdeen Press and Journal – Friday 10 November 1939

10] Nottingham Journal – Friday 15 November 1940

11] Nottingham Journal – Thursday 26 August 1943

12] Gas Producers, London Passenger Transport Board, 3/1943 – LTM 2014/3922

13] Liverpool Echo – Saturday 01 August 1942

14] Automotive News – 11th January 1943

15] The moving metropolis : London’s transport since 1800

16] Manual; Gas Producer Buses Manual for Maintenance Staff and Drivers, London Passenger Transport Board, 02/1944 – LTM 2014/3925

17] Experiment no. S5832 Road tests with Activated Coke, London Passenger Transport Board, 9/1943 – LTM 2014/3906

(There were also attempts to store gas in the buses, using large balloons, but that’s for another article)


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  1. Andrew Jarman says:

    The Germans used 500,000 Woodgas powered vehicles in WW2 The WP page is a good place to start if you are interested in the history of these vehicles,with%20a%20wood%20gasification%20unit.

  2. JP says:

    Well how about that? I never knew that there is a silver lining to clouds of carbon monoxide. Whilst it happily kills anyone unlucky enough to get near it, even a tiny part-per-million value, it can be used to power engines. I’m off to look up similar uses for the dreaded CO2 now. Thanks for another of your spark-your-interest articles.

    One more thing: littered? Littered! Have you seen how intricate and detailed gasometers are up close?

  3. Ron Sampson says:

    Such buses also ran in Maldon in Essex during the 40’s and often came to rest on the hill up to the town!

  4. David Miller says:

    There is a record of a Brighton & Hove Bus co , of the gas trailer exploding & blew the back of the bus off. The conductress was slightly injured but badly shocked . The upper de k passengers were rescued by the fire brigade be sure the stairs were blow apart.

  5. James says:

    Great article! 2 typos: trainer, booket

  6. David T says:

    Saw some lorries with a small producer gas unit in the corner of the back platform in operation in North Korea 5 years ago. Maybe there still are?
    Producer gas plant was also used by some large (e.g. farm) houses well away from piped gas supplies. I saw one about 45 years ago as a (non-working) exhibit at the museum at Calbourne Mill, Isle of Wight.

  7. al says:

    Also Croydon council lorries were using “sewer gas” to efficiently run their fleet during the war and late 40’s source = practical mechanics mag 1946

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