Most of the trains most people see every day roll on metal wheels guided by metal rails. Everything from majestic freight trains and regional commuter rail to New York City’s iconic subways are like this. Yet, sometimes you’ll find a different kind of passenger train, one that has pneumatic tires and rides on concrete rather than real rails. They look like guided buses, but why do they exist and why are you going to find a lot of them at airports? Once you learn about these trains you’ll see they make a lot of sense.
Our fearless leaders have been traveling across Europe and one thing has caught David Tracy’s eye. Deep in the Paris Métro, he spotted rolling stock known as MP 73 and MP 89 CC. Apparently, those alphanumeric names mean something and MP 73 is Métro Pneu appel d’offres de 1973, or a rubber-tire metro ordered in 1973. The MP 89 is the same thing but was ordered in 1989. But as their name implies, these aren’t any normal metro trains. As David observed, these things are rolling down flat surfaces using inflated rubber tires!
You don’t have to go to Paris to find other trains like these. Rubber-tire metro trains can be found in the Montreal Metro as well as so many airports from Germany to Taiwan and at nine additional airports here in the United States. If you’ve been to Denver International Airport or the Phoenix Sky Harbor International Airport, you’ve probably taken a ride on one of these trains. But why?
From The Dawn Of The Pneumatic Tire
As the National Museums Scotland writes, Scotsman Robert William Thomson invented the pneumatic tire and patented it in 1846 after utilizing the then-new process of vulcanization to produce rubber that was pliable, but not sticky. John Boyd Dunlop would later invent his own pneumatic tire in 1888, turning it into a revolutionary product for bicycles and later cars.
According to the book History Of The Pneumatic Tyre, Thomson saw his tire, named the Aerial Wheel, as being a perfect solution for horse-drawn carriages but also for rail. Thomson was a railway engineer and immediately saw advantages in having carriages ride on rubber. For horse-drawn carriages, Thomson felt his Aerial Wheel would lessen the power required to move carriages while also cutting down on noise. When used on the rails, the Aerial Wheel reduced noise and increased ride comfort.
Thomson’s vision for a railway version of the Aerial Wheel saw a train running on Aerial Wheels, which rolled down a board track. Steel wheels stuck around, but they were flipped on their sides and rolled down a central rail to guide the train down the tracks. Spanish engineer Alejandro Goicoechea, the founder of train manufacturer Talgo, patented his own version of the rubber-tire train in 1936.
Despite these early efforts, it was France and Michelin to make the rubber-tire metro train mainstream, from Michelin:
In the 1930s, the RATP (Régie Autonome des Transports Parisien) raised the question of equipping its subway trains with tires to improve transport conditions and facilitate the operation of these lines. It then naturally turned to the railcar imagined by Michelin who had just broken the record of the Paris-Deauville link in January 1931: the famous Micheline. Our collaboration with the RATP ended twenty years later, in 1951, with the circulation of the first metro on tires in the world, on an experimental line intended to test the innovations developed by the RATP: line 11 (Châtelet – Mairie des Lilas).
The benefits of this technical solution are quickly apparent: acceleration and braking are improved, which increases the speed on the lines offering short inter-stations. The trains run better on the slopes and are better at cornering, limiting the constraints. Tires also reduce vibrations and noise, for better comfort for travelers and residents! Vibration reduction also extends the life of the equipment, whether it is the rails or the bogies that make up the train.
So many qualities that will make the success of the metro on tires in France, then in the world. The same technology is adopted for rail shuttles serving most airports and is well suited for automated lines, which have been booming in recent years. When a public transport operator launches a “pneumatic” line, it commits itself for several decades. He therefore needs a reliable partner. Our 70 years of experience is a real asset, which explains why Michelin equips 8 out of 10 trains in the world.
Still Relevant Today
That middle paragraph is the important bit. Have you noticed how quickly airport metro trains can get you around?
As Michelin explains up there, trains running on rubber tires can get moving and stop quickly thanks to the much higher friction of rubber against metal or concrete compared lines to smooth steel wheels against smooth steel tracks. This helps to increase line speeds between stations. The tires also add track flexibility as they climb grades like cars do. I’ve seen airport systems climb hills and take the kinds of sharp turns a traditional subway train wouldn’t be so happy with.
As Railway News, the publication of French equipment manufacturer Texelis writes, the first generation of rubber-tire metro trains was the MP 55, which was built in a collaboration between Renault, Brissonneau et Lotz, and Alstom. In keeping with the theme I told you about early on, these trains were rubber-tire metro trains ordered in 1955 with deliveries beginning in 1956. One of the big advantages offered by the MP 55 was its ability to achieve higher speeds than the previous Sprague-Thomson steel wheel trains. A Sprague-Thomson achieved speeds of just 28 mph while the trains on rubber tires hit up to about 43 mph.
The French version of the electric rubber-tire metro uses both flat platforms for the tires to run on but also steel wheels and tracks directly next to the rubber tires. Here’s an example of a bogie for the MP 89 series:
Railway News reports that trains like these are still relevant today. These trains’ abilities to stop and go quickly, combined with modern signaling and control systems, allow a crowded metro like the one in Paris to operate trains with high frequency and closer together. Passengers also enjoy reduced noise since they’re riding on inflated tires rather than metal wheels.
Railway News continues its list of benefits by pointing out a rubber-tire train’s excellent climbing abilities but also reduced vibrations against the bogies, allowing a train manufacturer like Texelis to use cheaper, lighter materials. Finally, Texelis believes the rubber tire system is cheaper to maintain. Keeping the steel wheels around also offers redundancy in case a rubber tire blows.
Why Aren’t These Everywhere?
So, if rubber tires are so great for trains, why aren’t the primary form of passenger rail? You’ll also find trains running on rubber tires when you ride a Disney Monorail. Still, what gives?
A technical paper written by Matthew C. Harrison and published to SAE International gives us a good explanation. Let’s start with the downsides you’re probably already thinking about. Trains with rubber tires may not be proficient at their job when the path ahead is covered in ice. Tires can also blow out, which doesn’t happen with steel wheels.
Then the SAE paper digs deeper. Trains running on rubber tires require more energy to move than their steel-wheel counterparts. There’s also the higher maintenance of needing to replace and servicing several tires. You’ve probably also noticed another problem and it’s the fact that these trains still use steel rails and wheels for guidance and redundancy, so railways don’t save money when it comes to trackage. To put this into perspective, one student paper from McGill University found that the Paris rubber tire metro runs 2,688,000 miles per $1 million in maintenance, but Toronto is able to go twice the distance for the same money on steel wheels.
(Correction: The original version of this story mixed Toronto with Montreal. Toronto is the one with steel wheels.)
Other noted downsides include the fact tires break down into particles which add to pollution and that while rubber-tire trains are smooth, steel wheel trains running on well-maintained tracks are still smoother. Our own Adrian Clarke also points out that tires aren’t great when you’re dealing with really high loads or intensity. Apparently, all the heat generated by the tires is also a problem. Putting all of that heat energy into underground tunnels means some of these trains cannot have air-conditioners, because AC would add even more heat into the mix.
These trains are relevant today, but they’re best for specific use cases like carting people around airports or providing lots of train intervals in a metro system. Otherwise, old-school steel wheels and rails still win out for operations.
So, the next time you’re at an airport or one of the many cities in the world with metro trains running on rubber tires, you now know why. You’re going to be whisked away to the next station quickly and quietly thanks to the same tech that allows your car to get you around.
(Images: David Tracy, unless otherwise noted.)
Steel wheels may not go flat like rubber tires do, but they are susceptible to flat spotting (when they lock up, for instance). The way they get fixed is to put them on a giant lathe and turn them down. https://www.youtube.com/watch?v=WcpKlMd5p8U
I just flew home from Paris. Love their metro – hate their ticketing.
My first question when starting to read was, what about cornering; steel train wheels are shaped so that the effective diameter changes as they shift sideways on the rail so that the outer wheel of a pair on a solidly-connected axle accommodates the larger arc and vice-versa, but that’s not going to happen with tires running on a flat surface. Question answered with the photo of the bogie, they use geared differentials same as a truck or car. An important difference which also would add to cost.
“The tires also add track flexibility as they climb grades like cars do.”
Nuremberg, Germany came up with better solution that helps its U-Bahn subway trains accelerate faster from one station with less electricity and brake with less effort before arriving at the next station. The tunnels between the stations were constructed like a rope tied at both end with lot of slack in the middle.
The Nuremberg’s U2/U3 line was Germany’s first fully automated subway system (excluding the people movers shuttling between the aeroport terminals) and world’s first system to allow both automated and manual control (with human operators) on same lines. The automated trains have no operator compartment so passengers have the unobscured front view that give them the awesome view of tunnel going down from one station then going up before the next station.
I understood that the reason was because of the difficulty of having access to steel after the Second World War. The construction of the subway with tires required much less steel than a normal subway.
When visiting Paris, I was told that the reason for making metro line running on pneumatic tires, was to minimise vibrations transferred to surrounding ground and buildings. Its seems plausible that there was need to preserve historical buildings, and tunnels were planned not as deep underground as other lines. Rubber wheeled trains mostly have downsaides of added complexity, and not beilng compatible to the rest of railway system, but trasnfer a lot less vibrations to the ground.
can they do a burnout?
I can confirm two of the downsides. The Montreal Metro is one big underground oven. I don’t know if they even have ventilation shafts, which might help. Being underground in mostly solid rock is hot.
Also, the tire dust is prevalent. You’d almost think these were diesel powered trains.
“The Montreal Metro is one big underground oven. I don’t know if they even have ventilation shafts, which might help. Being underground in mostly solid rock is hot.”
Also humid, at least it was when I rode it.
It’s especially awful in the winter when you come in from the cold wearing a heavy coat and then you absolutely swelter down there and then you go back out in the cold all sweaty.
Same with Paris Métro during the hot days, especially the older ones that were built with cut-and-cover method so close to the streets. The asphalt surface on the street retains lot of heat and transfer it to the subway tunnels and stations.
Over here in Ottawa, I’d gladly take rubber tire trains over the fustercluck that is our current LRT. The boondoggle to end all boondoggles.
At least you got an LRT. In Toronto we just got a permanent construction site.
…with rail alignment issues. LOL
Weren’t PPPs supposed to be a panacea to getting things done faster, cheaper and more efficiently?
Mercedes, you have the McGill report overview misquoted. The Montreal metro is rubber wheels and the paper is comparing it to Toronto’s steel wheeled subway.
Great article!
D’oh!! I’ll fix that, thank you!
This is a heck of a piece of work, Mercedes, thanks!
I’m not sure the Montréal Metro is the control for steel wheels. My recollection is that Montréal is all rubber tired. Paris has a mix of rubber tired and steel wheeled lines plus some lines are driverless. Rubber tires are a good option for some passenger applications because of MVH and traction. For freight, long distance passenger traffic and very heavily utilized metros steel is real
The Montreal Métro is rubber-tired, as it is only underground and “indoors.” The new REM (Réseau Express Métropolitain) is a new steel-wheeled light rail system that runs outdoors into the suburbs, though only part is completed. There’s also the “Train de banlieue de Montréal,” the heavy rail commuter rail that runs further out from Montréal.
The Montréal metro is indeed all pneumatic. That is actually one of its perks, as well as the individually unique stations (architecturally / artistically speaking). I’m also pretty sure Montréal’s use of a rubber-riding system was indeed inspired by Paris’ use of such a system.
Considering that the Montreal metro was designed by Alstom, a French company.
Yes, Alstom indeed. And the newer (still pneumatic) ‘Azur’ cars are Bombardier.. Which ironically was bought out by… Alstom. (Of which the provincial pension fund has like 30% of shares? I might be wrong on the number). Bombardier would still have its trains division if it wasn’t for the crippling development costs of the c-series airplane program, an excellent aircraft that got F’ed over by Boeing and Trump 300% tariffs… So Bombardier sold its trains division, GAVE the c-series to Airbus (it’s now the A220) and now only makes private jets.. The fall of a giant.
That sucks. As a Canadian, I funded most of that failure.
The steel wheels are the “negative connection” for the electricity. Maybe backup control if the direction rubber wheels.
I dunno, are airport people-movers technically trains? I guess when you have a couple of them hooked up together, but if it’s a single unit that’s just a bus that runs on a guideway.
https://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/PHX_SKY_TRAIN.jpg/1920px-PHX_SKY_TRAIN.jpg
That said, the line between buses and trains has always been fuzzy, so I shouldn’t be getting all pedantic about this. I mean, Adelaide does still have an O-Bahn after all.
“I dunno, are airport people-movers technically trains?”
Yes since a train is really just a series of connected vehicles.
Are semi trucks(or anything else towing a trailer) trains? They are a series of connected vehicles.
If they have more than one trailer, then yes. They’re known as Road Trains.
https://en.wikipedia.org/wiki/Road_train
Don’t see any connections on this one.
https://upload.wikimedia.org/wikipedia/commons/7/77/Bombardier_CX-100_exterior.JPG
Well that’s just an individual train car waiting to be hooked up to other cars to make a train set. You can see in the picture in front that it has the provision for it.
I mean, I fully acknowledged my pedantry in the original comment so I’m not really trying to achieve anything meaningful here. That said, is this a train, too?
https://live.staticflickr.com/65535/8895923330_62a0b57d86_h.jpg
No. That is an articulated bus. it’s “not a train” in the same way this is not a train:
https://stevemunro.ca/wp-content/uploads/2023/08/4604_20230809_hillcrest.jpg
That is an “Articulated Tram” or “Articulated Streetcar”
Feel free to carry on with the pedantry… I don’t mind.
But then are trams trains because they ride on rails!? I guess they’d be ‘railcars’ to be extra specific about it. And what about an RV towing a car?
https://media.ed.edmunds-media.com/non-make/fe/fe_919171_1600.jpg
If you go by the dictionary definition, a set of vehicles (rolling stock) going down a track is a train. These rubber tire metros follow tracks, so they’re trains. I guess trams are also technically trains. But RVs and articulated buses are not trains.
BUT! Then you apparently have other categories of trains like road trains. Look, I prefer not to think about this too much. 🙂
“If you go by the dictionary definition, a set of vehicles (rolling stock) going down a track is a train.”
It doesn’t need a track to be a train. Case in point… the ‘train’ you can take at the Canadian National Exhibition which is happening next month:
https://www.toronto2anywhere.ca/wp-content/uploads/2024/04/CNE-Train.jpeg
No… a train can have tires or be on rails. And you are correct… it being on rails makes it a ‘rail car’. And a tram is a form of rail car.
And remember on Top Gear how they modified cars to run on rail road tracks? All that mean was they were converted from being ‘road cars’ to ‘locomotives’. And they didn’t become ‘trains’ until the added the camping trailers/caravans converted to rail use
https://www.youtube.com/watch?v=mkpCzp0CmjY
And a car being towed by an RV would be a dinghy. And here are lists for vehicles suitable use as a dinghy behind an RV:
https://www.roadmasterinc.com/media/dinghy-guides/
And calling it a ‘dinghy’ comes from the boating world related to a small boat either carried or towed behind a much larger boat
https://en.wikipedia.org/wiki/Dinghy
Is a moving sidewalk a sidewalk if it is in the middle of the pathway? Wouldn’t it be a moving roadway? Oh yeah, people mover. Wide open category.
On a related note… if you have a tree in the forest and it is cut down and chopped up, at what point does the tree stop being a tree and is just ‘fire wood’?
Out of curiousity, does anybody know of an airport train system that is NOT on rubber tires? Every one I can think of like Chicago, Atlanta, Miami… use these.
Welcome aboard the Plane Train!
Or the rental car train: “Thank you for choosing Hartsfield-Jackson International Airport!” Look, If I had a choice… it would not be you. I loathe ATL but not enough to drive to ‘Nooga.
The heavy-rail MARTA trains are on steel. And you sure know it.
The New York JFK “AirTrain” uses standard gauge (1435 mm) track.
Michelin have an exhibit about this in their museum, and from tone you can tell that they are incredibly peeved that it didn’t take off.
Hey guys, what if we swapped these out for some BFG All-Terrain KO2s, add some lights and a roof rack? #MétroSafari
That would make for a killer overland train! Wait a minute……
https://en.wikipedia.org/wiki/Overland_train
Hartsfield-Jackson’s plane trains are this design! I only learned this because there is an awesome train/bus museum north of Atlanta that has a plane train on display. The Southeastern Railway Museum is so awesome! You get set loose to go poke around almost everything. MARTA buses from decades past? Open to you. Dozens of old Amtrak sleeper cars? Go wander through opening bunks, checking out seats. Plane train? If you can hoist yourself up you can enter!
There’s steam trains, diesel engines, a train of nothing but cabooses. It’s a brilliant playground with an alarming lack of supervision. Go see it if you’re in Atlanta and see one of these neat trains up close!
Wow, I have lived here for ten years and had no idea that this Southeastern Railway Museum even existed!
The big one in Green Bay WI is pretty great too.
Lots of hot train action here on Traintopian lately!
I saw the headline about a train with rubber tires and was, like, you mean a bus?
TLDR: Rubber Tire having trains exist for frequent stops, as rubber tires have more friction than steel wheels, allowing them to stop quicker. Said extra friction makes them inefficient for travel with infrequent stops.
Hmm. I never knew about this option. I don’t really see “regular” wheels as all that harsh. I mean, if we are supposed to go green, rubber wheels seem like a terrible trade-off.
It just seems so labor intensive. It’s cool and all that, but it’s not really a surprise that it’s a French innovation. It’s all very French, if you catch my drift.
I mean, at least it’s not a Canadian idea.
Rubber wheels on a train with 200 passengers are already a lot better than no train and rubber wheels on 100 cars.
Baby steps
Ok. Think about the logistics of having rubber wheels.
There are already plenty of procedures in place to detect flat spots on steel wheels. How fast do you think your train is going to go, when the conductor has to manually inspect and test the PSI of each wheel.
Not to mention when travelling in high-speed territory, going 75mph-ish, and some goofball throws tacks on the track.
I could go on for hours here. lol. It’s a dumb idea. It’s French. I am French. I know of what which I speak.
I’m pretty sure these trains can have TPMS installed and regular inspections can detect damage before failure.
They also aren’t regular car tires, they probably have like 4inches worth of rubber before you can pierce them.
These are mostly for subway and light rail, which definitely don’t hit speeds anywhere close to 75mph.
I remember being terrified of the NYC Subway at a young age because of the constant screeching sounds from the wheels. Then my dad moved to Washington DC, and I was surprised when their subways were significantly quieter.
If you want to hear some REAL screeching, take a trip on the MBTA Green Line in Boston. The underground sections are deafening.