Back in the 1970s, America’s cities weren’t as cozy as they are today. Dense smog clouded the views of the beautiful skylines of Los Angeles, New York City, Chicago, San Francisco, and more. This pollution wasn’t good for the millions of people who had to breathe it. Since 1959, the California state government has been working to reduce pollution from vehicle emissions, and in 1972, the state embarked on an ambitious project. The steam engine was believed to be a possible replacement for the dirty diesel engines of the 1970s, and to test it out, multiple cities converted city buses to steam power.
Back in 1943, the South Coast Air Quality Management District writes, Los Angelenos were forced to deal with an enemy they could not fight. Plumes of smoke and fumes blanketed Los Angeles right in the middle of a heatwave. According to the Los Angeles Times, visibility was as low as three blocks. Meanwhile, residents complained about having stinging eyes and “scraping” throats.
What the city experienced was nothing new. For 40 years by that point, Los Angeles found itself draped in so much smog that, in one case, residents mistook a giant cloud of pollution for a solar eclipse. What happened in 1943 was in part a result of the rapid industrialization of American cities during World War II. As plants roared with the sounds of machinery, all kinds of toxins were released into the air. Meanwhile, car ownership was also hitting all-time highs, and what came out of their tailpipes only contributed to the mess.
Scientists conducted research into the causes of the smog, finding that the causes were vast, ranging from toxins released by factories and car exhaust to burning trash, diesel engines, and locomotives. The mountains surrounding Los Angeles and the city’s largely stagnant winds made the situation even worse. Reportedly, there were so many awful chemicals in the air that car tires in California degraded faster than they did in other places.
In 1947, the Los Angeles County Board of Supervisors established America’s first air pollution control program. By December 1959, the state of California became the first in the nation to enact vehicle emissions standards. The standards set by the California State Department of Public Health targeted hydrocarbon (HC) and carbon monoxide (CO) tailpipe emissions and helped lay the groundwork for the landmark Clean Air Act of 1963, which was the first federal legislation that permitted the government to combat pollution.
At first, California’s emission controls did not include diesel vehicles, which were seen belching out black smoke on the state’s roads. In the late 1960s, as California sought to lower tailpipe emissions even further, the diesel engine was also targeted. One of the solutions pitched to lower diesel was to get rid of the diesel engine entirely, and going back to an old friend of locomotion: Steam power.
The Idea Of Steam-Powered Buses Wasn’t That Crazy
According to the Assembly Office of Research of the California Legislature, the idea to make buses run on steam did not materialize out of nowhere:
During 1967-68, studies and hearings by both state and federal agencies revealed that certain alternatives to the internal combustion engine (ICE) might be feasible as low-emission automotive powerplants. One alternative is the external combustion engine (ECE), in which fuel is burned continuously and completely to generate power. There are several types of ECE, but the most familiar is the steam engine, technically known as a Rankine cycle engine. The studies and hearings suggested that the ECE, far from being an outmoded concept, could become a workable alternative to the ICE, with the aid of modern technology. With this in mind, the California State Assembly decided to sponsor the demonstration and evaluation of ECE propulsion systems. This work was supported in part by a grant of funds from the Urban Mass Transportation Administration of the U.S. Department of Transportation.
The purpose of the California Steam Bus Project was to evaluate the technical feasibility and public acceptance of the ECE as a low-emission, quiet propulsion system, using city buses as demonstration vehicles. Emphasis was to be placed on the early demonstration of potential, rather than extensive development or technical perfection. The title “Steam Bus” was adopted after the project’s engineering contractors chose Rankine cycle systems to exemplify the ECE.
As Roy A. Renner, an engineer with International Research and Technology Corp., wrote in a paper published in SAE Transactions, there was precedent to go with steam power:
Steam-propelled road vehicles have existed for over 200 years. The French engineer Cugnot demonstrated a 3-wheeled artillery tractor during the 1760s. Steam-powered stage coaches (the first steam buses) were operated commercially in England in the first half of the nineteenth century, although they were rapidly superseded by faster and more efficient rail conveyances. The birth of the true automobile occurred during the 1890s. Until around 1910, many observers regarded steam power as superior for road transport. Lightweight, high-torque, and silent steam engines were invented and manufactured by the thousands. Steam cars were displaced by the gasoline-fueled internal combustion engines (ICE) when the latter evolved into forms that were cheaper, simpler, and more convenient to use.
Interest in the latent possibilities of steam was not totally forgotten, however. The work of Doble, Besler, Williams, and others in the interim years may yet prove to be forecasts rather than of historical interest only. Returning to bus applications, the London public transit system operated some hundreds of Clarkson steam buses until 1919. These vehicles were fueled by kerosene, and employed condensers for the recycling of the water.
The Doble technology found its way into city buses, presaging the present California experiment. During the early 1920s, the Detroit Motor Bus Co. operated two Doble-powered buses for over 30,000 miles. These vehicles had an acceleration rate which was greater than that of contemporary gasoline buses, and with a fuel consumption which was competitive. In 1929, the Doble Co. installed a steam system in a General Motors Yellow Coach. During the mid-1930s, high-grade motor fuels were in short supply in the German Third Reich. Warren Doble worked closely with the Henschel works at Kassel to introduce “Dampfomnibusse,” which could burn fuel oils derived from coal. One such bus prototype is shown in Fig. 2. The direct-drive and reversible steam engine developed a rear-wheel torque which was greater at all road speeds than the competing ICE with 4-speed transmission.
With the stage set, it was time to make modern steam-powered buses a reality.
Converting Diesels To Steam
According to the California State Legislature’s Assembly Office of Research, development began in earnest in 1970. To provide researchers and evaluators with a broad set of choices, three contractors were selected to partner up with a transit organization, and each contractor was encouraged to explore different designs to achieve the same result.
William M. Brobeck and Associates of Berkeley, California, teamed up with the Alameda-Contra Costa Transit District in Oakland. Bill Lear’s Lear Motors Corporation of Reno, Nevada, partnered with the San Francisco Municipal Railway (MUNI). Finally, Steam Power Systems of San Diego, California, hooked up with the Southern California Rapid Transit District (SCRTD) of Los Angeles.
All three contractors were given a mission to remove diesel engines from standard General Motors and Flxible 40-foot transit buses and replace them with steam external combustion engines. Renner’s paper describes what sounds like chaos as engineers tried to figure out the best way to build a steam bus:
Reciprocating, rotary, and turbine expanders all reached the preliminary bench test stage. A number of working fluids other than water were examined and some were used in bench-test powerplants. Several variations of control systems, auxiliary drives, feed pumps, and burners, went on to the expensive junk pile. The present systems have some features in common. All use water as the working fluid. All generate the steam in forced-circulation, continuous-coil tubular steam generators. Final control of the steam temperature is by the “normalizer” principle, in which supplemental feed water is injected into the superheater as required. Condensing is by fan-cooled, finned tubular radiators. As an expedient in this short-term endeavor, all three buses use commercially available multi-ratio automatic torque converter transmissions. In each case, the main expander (engine or turbine) drives auxiliaries and accessories at idle. While a variety of liquid fuels may be used, most testing was conducted with No. 1 diesel.
Renner then detailed the design each contractor landed on:
The Brobeck system is an outgrowth of the automatic monotube steam generators and compound-expansion piston engines developed earlier by Doble and Besler (10). The steam generator and its automatic controls are mounted in the original engine compartment at the rear of the bus. As shown in Fig. 3, the other systems elements are located amidships under the floor. All accessory and auxiliary units are belt driven from pulleys on the forward end of the engine crankshaft. Condenser fans are remotely driven by hydraulic motors. The transmission is a Dana- Spicer model 184 2-speed torque converter unit, locking up into direct drive at 29 mph.
Approximately one-quarter mile of tubing is used in the steam generator, varying from 0.50 in OD in the economizer section, to 1.0 in OD in the superheater. In order to reduce pressure drop through the generator, two parallel tube paths are used in the economizer and most of the evaporation zone. These are merged into a single monotube coil in the final evaporation and superheating regions. Both tangential and axial burner firing were tried, with the former yielding better results in this generator configuration. The burner uses a single air-atomizing nozzle, with automatic switching among four steady-states: off, idle, low fire, and high fire. The engine (expander) has three double-acting cylinders (Fig. 4). Compound expansion is utilized, with one high-pressure cylinder exhausting into two low-pressure cylinders. As an expedient for this early demonstration, a nonreversible fixed cutoff valve gear is used. By locating the system components in existing spaces, the original seating capacity (51 passengers) was retained.
The [Steam Power Systems] powerplant (11) features a 6-cyl double-acting compound-expansion engine. The steam is reheated between the two expansion stages. Steam generation is by a series-parallel tubular boiler, with an additional section for the interstage resuperheating. The steam generator, expander, auxiliaries, and one of the condensers, are located in an enlarged rear-engine compartment. Three additional condenser cores are located under the bus, just behind the front axle. Fig. 7 shows the system installation. Of the three buses, this is the only one to retain the original transmission (GM-Allison Super V) and angle drive rear axle. It is also the only bus equipped with air conditioning. Two significant innovations were carried to the bench test phase, but were laid aside temporarily when time did not permit sufficient development to allow installation into the bus. One of these was the use of infinitely variable cutoff valve gear, and the other was the elimination of oil lubricants in the steam cylinder. The firstof these allowed engine speed control without a throttling valve and would be conducive to high-thermal efficiency. The second would avoid the old problem of oil carry-over into the condenser and boiler.
Bill Lear – famed for inventions like the Lear Jet and the automotive eight-track player – took a very different path than the other two contractors. The other two buses used reciprocating steam engines like old steam locomotives did. Lear’s design was a newer technology used in railroading that remains in use for power generation: the steam turbine.
Before we get into how Lear made its bus, let’s look into the basic function of a steam turbine. In a basic steam engine, a fuel like coal, wood, or oil is burned in a box. The heat from this fire is funneled through flues, which heat water in a boiler. The boiling water generates steam, which is under pressure since it’s in an enclosed vessel. This pressurized steam can then be directed to cylinders through slide valves. The piston can then be attached to other mechanical components to drive a locomotive, ship, or industrial machine.
In a steam turbine, the steam now drives a turbine instead of a piston and cylinder, resulting in rotary motion. An invention of the 19th century, steam turbines run faster, more efficiently, and quieter than steam engines while being smaller than equivalent steam engines.
Now, let’s look into how Renner explains the Lear turbine bus:
The Lear power system differs strikingly from the other two, in the use of a turbine as an expander. All major components are placed in the original rear compartment. It was necessary, however, to enlarge this compartment because of the shape of the steam generator and
to accommodate regenerators. Lear’s steam generator features a radial outflow of the hot gases through the tube bundle. During the development period, several types of burner were tried, including vaporizing mechanical atomizing, and air atomizing. An air-atomizing burner was finally adopted.So far as is known, this vehicle is the first in history to be successfully propelled by a steam turbine. Originally, this turbine was designed to operate on an alternate working fluid having antifreeze characteristics and a molecular weight greater than that of water. During bench testing, however, it was found that this fluid deteriorated chemically at the required operating temperatures. Steam was then substituted, with redesigned turbine nozzles. The single-stage impulse turbine is very small in size (wheel diameter 5.6 in) and rotates at high speeds (to 65,000 rpm). Reduction gearing of 24:1 ratio connects the turbine, via an Allison HT-740 D 4- speed automatic transmission, to the rear axle. Most of the auxiliaries are also driven from the speed-reducing gearbox, including the feed water pump, two condenser fans, and the burner blower.
Renner is technically incorrect with the assertion that the Lear turbine bus was the first vehicle in history to be successfully propelled by a steam turbine. There were steam turbine locomotives as far back as the 1930s.
Apparently, this wasn’t Bill Lear’s only steam project, either, as he would power a Chevrolet Monte Carlo using a steam turbine and built a steam turbine-powered racecar that entered the 1969 Indianapolis 500.
The Buses Were Promising
William M. Brobeck and Associates was the first to finish its bus, delivering a functional vehicle to AC Transit in fall 1971. Lear was next, and his bus was finished in January 1972. Finally, in March of that year, Steam Power Systems finished its bus. All three contractors had to work under tight parameters. No flammable, explosive, or toxic fluid could be used. The steam generators had to be designed to be inherently non-explosive, a variety of temperature and pressure safety switches and valves had to be installed, the turbines had to have overspeed governors, and driver controls had to be as similar to a diesel as possible. The contractors weren’t even able to use large pressure vessels out of safety concerns.
The results were promising. The steam buses made between 180 HP and 225 HP overall and were shown to have performance characteristics on par with diesels. The steam buses had slightly lower top speeds and took longer to accelerate, but were also much quieter and smoother than the Cummins and Detroit Diesel-powered buses they were compared with. The fastest steam bus, for example, came from SPS, and achieved a top speed of 58 mph. It took 71 seconds to reach 50 mph, or 14 seconds longer than a bus with a Detroit 6V-71. Overall, it was found that the steam buses were roughly comparable in performance to a bus with a six-cylinder diesel, but much slower than a bus with a V8 diesel.
Check out this promotional video:
In testing, it was found that the steam buses were 2.5 to 10 decibels quieter than the diesels when sitting still and up to 14 decibels quieter when on the move. Sadly, the quietness was largely limited to the exterior, as the steam buses were found to be as loud or even louder inside than diesel buses.
What really looked good was emissions performance.
Analysis had shown that the cleanest steam bus produced 30.5 percent less CO and 86 percent less HC and NO2 than the cleanest diesel bus. In other words, the program produced the result it was hoping for. Collectively, the buses would drive a total of 8,372 miles on public roads, with around 800 of those miles in passenger service. Each contractor even managed to ensure that the buses had regular diesel-like controls and that the steam turbines were ready to roll in six minutes or less. The bus drivers even fired them up entirely from their seats like they would diesels.
So, what went wrong? If the worst trade-off is that the inside was a little louder, why aren’t there steam buses out there today?
Running Out Of Steam
As it turned out, the experimental steam buses were great on paper, but still needed a lot of work.
The first problem was fuel economy, or lack thereof. In testing, it was found that diesels got two to three times better fuel economy than the steam buses did. At 20 mph, the diesels did between 4.7 mpg and 7.7 mpg while the steamers did no higher than 2.2 mpg at the same speed. At 30 mph, the disparity grew, as the diesels got between 7.1 mpg and 11.8 mpg while the steam buses got no higher than 3.5 mpg. In fact, 3.5 mpg was the highest average reported by the steam buses, and most of the time, they got in the mid-2 mpg range, regardless of driving speed.
Idling was even worse. At idle, the steam buses consumed 4.7 gallons of fuel per hour compared to only 0.65 gallons per hour for the thirstiest diesel. The data also showed that Bill Lear’s novel steam turbine bus struggled pretty hard. His bus tended to be slower, louder, and thirstier than the other steam buses in the test.
If all of that wasn’t bad enough, two of the buses were also quite unreliable. The Alameda-Contra Costa Transit District bus suffered an engine failure on its very first day of service. Repairs took five months, then the bus was put back on the road in May, 1972. This time, the bus survived eight days of use, but generated complaints about control instability, a blower motor failure, a feedwater pump failure, a relief valve bellow failure, and unexpectedly high water consumption.
The bus went back to the shop for more improvements and returned to public service in September, 1972. It then ran for nine days without any mechanical failures. This bus traveled a total of 3,465 miles during the testing program.
The San Francisco Muni Railway steam bus was a beast, and enjoyed 11 days in revenue operation. During this time, the bus climbed 19 percent grades, ran down the highway in traffic, and carried loads of 98 passengers. The only operational issues with this bus were a boiler modification to reduce smoke and a fan belt that came off. This bus was even driven 230 miles across the Sierra Nevada to Reno without issue. Overall, it traveled 3,900 miles. As it turned out, Bill Lear’s bus was the slowest, thirstiest, and loudest, but it was by far the most reliable of the three.
Then there was the SCRTD unit, and this one was a disaster. It couldn’t even complete its first two attempted days of service due to an oil pump failure and a bolt shearing off the combustor fan. It finally completed only one successful trip of 7.3 miles in September 1972, just to get sidelined because a fan in the boiler failed. Just a day later, the SCRTD team discovered a boiler leak. They decided to use the bus for performance tests for a few more days before the leak got worse. The bus managed to get only one more day of revenue operation before the steam bus testing period ended on September 30, 1972.
They Needed More Time To Cook
It wasn’t all bad. When surveyed by researchers, most riders, fleet managers, and drivers all preferred the steam buses over diesels. Drivers and riders in particular loved the smoothness and quietness of the steam buses.
The Assembly Office of Research concluded that the $8 million experiment ($65,002,822 in 2026) was a success. The contractors really did make steam buses that drove like diesels, but were far cleaner. The researchers believed that, with more investment, the contractors could work out the kinks to get better reliability, better fuel economy, and better performance out of their steam buses. It was believed at least another $20 million ($159,785,645 today) was needed for further research over four years.
Ultimately, this did not happen, and the Steam Bus Project concluded on September 30, 1972. The oil shock of 1973 was the final nail in the coffin, as getting 2 mpg was now untenable in a world of fuel shortages, even if steam engines didn’t burn gasoline. Bill Lear had grand ideas for a futuristic steam-powered bus of his own, but even his research came to a halt in the aftermath of the oil crisis.
While the Steam Bus Project was ultimately a dead end, the San Francisco Municipal Transportation Agency says that it was one of the catalysts for the movement to improve diesel engine cleanliness and fuel economy. The program had proven that Californians desperately wanted better air and were willing to invest in clean air projects.
Honestly, it’s amazing that this project even happened in the first place. Three contractors took regular buses, tossed out their diesel engines, and then strapped steam engines to them. Steam engines were a bit of an anachronism even in the 1970s, so to see compact steam engines living in the back of sleek transit buses must have been a shocker to the few people who got to see it back then.
But the project also made sense. The mission was to reduce emissions, and that part was a smashing success. A part of me wonders what things could have been like had the fuel economy issue been figured out. Would steam have had a comeback?
Top graphic image: ACT268; Creative Commons Attribution 2.0 Generic
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