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In the last few weeks, I've taken a lot more trams than I normally do, in a few different countries. Some of those trams have had low floors, allowing me to just step on / step on wheeling some luggage. Others have involved climbing up several steps to get in, often struggling with luggage.

The low floor accessible trams haven't only been handy for me when I've had luggage, they've also looked nice and easy for families with prams / pushchairs, wheelchair uses, old people with mobility problems etc. I've spotted very few people in those categories struggling their way onto the high floor trams, and the surprised looks I've tended to get hauling my suitcases up into them seems to indicate that most people don't even try...

I'm guessing that people buying trams don't just go "I know, let's buy a tram that isn't accessible just for fun", and there must be a good reason why many trams out there are high floored and non-accessible. What is it?

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    Speculation: 1: Cost. 2: In a high floor tram, the motor can go under the floor. In a low floor design, where do you put it? (See 1.) 3: Many trams run on routes that include developed stations with platforms that will be designed for an appropriate floor height. – Nate Eldredge Dec 9 '14 at 3:52
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    Isn't it simply a matter of technology and requirements? Most high-floor trams are old, designed at a time accessibility was not a priority and maybe pieces were bigger (and so harder to hide under a seat/too heavy to put on the roof) – Vince Dec 9 '14 at 4:10
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    It should be noted that high-floored does not always equal non-accessible, if all platforms are elevated. – O. R. Mapper Dec 9 '14 at 9:23
  • And another bit of speculation: In some German cities, tram systems provide service not only for downtowns, but also to nearby cities. That means that they are structured in a way that within the city, they act like true trams, using rails in the middle of the street between cars, while they go on normal railroad tracks outside of cities, together with other trains. While in general, the tracks are kept free of obstacles, it is possible that for safety reasons, those trams need to have the same distance between floor and tracks as all other trains. – O. R. Mapper Dec 9 '14 at 9:29
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    @O.R.Mapper, there usually is no restricting requirement as to the distance between floor and rails on the railway. Kassel's RegioTram, for example, uses low-floor trams. What may be of more importance, is the requirement that all rolling stock admitted to the general-use railroads must comply with very strict norms of resistance to collisions. It may be an extremely trying engineering task to design a low-floor vehicle that won't fold like a cardboard box after a collision with a hopper van full of coal. – ach Dec 9 '14 at 10:05
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From an engineering point of view, a tram is a vehicle that takes electricity from somewhere (overhead wires or third rail underneath), use motors to convert this into torque, and spins wheels to move the tram. The obvious solution is put all this machinery at ground level, right next to the wheels, and put the passengers on top. Ta-dah, a high-floor tram.

If, on the other hand, you want a low-floor tram, you've got to figure out some way to hide this machinery somewhere else, so passengers can use the space near the ground, but still feed the power to the wheels. This is tricky and expensive, plus the tram can get top-heavy and unstable if you stack everything on top. One mitigation is to fix some of the wheels in place, so they require less space, but then the turning radius of the tram also becomes larger, because the wheels can't turn sideways.

That said, this is largely considered a solved problem these days, so virtually all new trams are low-floor. However, trams are expensive and last decades, so replacing old rolling stock takes a good long time. And if you've attacked the problem from a different angle and built elevated stops to make high-floor trams accessible, the same high stop is no longer compatible with low-floor trams!

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    +1 on stability point. As an anecdote I worked for a company who tried to get into tram development (its main industry was different). As story was told to me their prototype kept flipping on turns because they couldn't get center of gravity low enough. And that was the end of it. :) – Rarst Dec 9 '14 at 10:08
  • With an entrance in the middle of the tramcar and the mechanicals hidden under the ends (where the bogeys would be anyway) you could easily have low-level access with a step or 2 up to a few seats at each end. The cost would be greater than a flat high floor but not massively so. You could even have doors at platform height and ground level. Double-decker trains do something similar. – Chris H Dec 9 '14 at 19:29
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    @ChrisН, Actually,that design is not unheard of. Some early examples of it may be traced back to 1920s. In 1990s and early 2000s some cities modernised their old trams in this fashion as a cheaper way to introduce low-floor services to their tram systems. You can still see cars like this in Prague or Helsinki. – ach Dec 9 '14 at 20:40
  • "trams are expensive and last decades, so replacing old rolling stock takes a good long time" pretty much nails it I guess. – Martin Ba Dec 10 '14 at 8:41
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Cost, and speed.

Some public transport companies report that low floor trams have 15% higher maintenance costs for the rolling stock, and 20% higher maintenance costs for the infrastructure on average (source in German).

The low-floor designs typically also decrease the speed at which a tram can drive through a curve (usually 4–15 km/h in 20 m radius curve)

There's also quite a good article on Wiki about Low-floor trams.

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The general answer is, because rail-borne rolling stock is expensive, it is only rational to expect trams to have a long life cycle. It is not unusual to see trams which are 30 years old, and in some places you can meet trams built in something like the 1930s and still in use.

Thus, because low-floor tram designs are relatively new (introduced in 1980s and only ripened in 2000s), the share of high-floor trams must necessarily be sufficiently high still, even in the most advanced cities.

However, some tramway systems have features that make it impossible to use low-floor cars. For example, San Francisco's Muni Metro or Düsseldorf's Stadbahn have underground stretches where stations have high platforms. Unless those stations are rebuilt (which may be prohibitively expensive), they are bound to use high-floor cars.

There may also be less obvious reasons to use high-floor trams.

We might go into further specific details if you tell us about which particular cities made you ask your question.

Update:

The particular cities named were Budapest and Melbourne.

Both cities have very extensive tram networks (Melbourne's is the largest in the world). Their fleets are numbered in hundreds of cars and can only be replaced gradually.

Budapest, as far as I know, has not been showing a quick progress in this matter because most of their money went into the construction of a new metro line.

There are no special features impeding the use of low-floor trams that I ever heard of.

  • Cities in which I have lugged suitcases up into high floor trams in the last month include Melbourne and Budapest – Gagravarr Dec 9 '14 at 9:31
  • There are large tram line (re)construction projects ongoing in Budapest, the new/renewed lines will be served by new low-floor CAF trams. – molnarm Dec 9 '14 at 10:30
  • I've seen both low and high floor trams in both cities, and been forced to carry luggage up steps in both, which in part inspired the question! – Gagravarr Dec 9 '14 at 11:43

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