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Rocket Talk: How Come Some Streetcars and Subway Cars Squeal?

By Torontoist

Have questions about the TTC? Rocket Talk is a regular Torontoist column, featuring TTC Chair Adam Giambrone and Director of Communications Brad Ross’s answers to Torontoist readers’ questions. Submit your questions to rockettalk@torontoist.com!

20090217rockettalk.jpg
Photo by spotmaticfanatic from the Torontoist Flickr Pool.

Reader David Wright asks:

I’m sure I’m not the only one to notice, but there’s a very (often painfully) loud squealing noise while subways come to a halt and streetcars turn, but it doesn’t appear to happen to all streetcars/subways. What’s the cause of the noise and is there any plan to fix it?

TTC Director of Communications Brad Ross says:

Good question. And a frequent one, too. Of course, nothing is simple, so bear with me (I’m no engineer as you’ll soon discover) as I do my best to explain both the causes and the solutions to this aural assault.
Let me start with brakes. Streetcars and newer subway cars (H6s and T1s for the geeks) use an electric, regenerating braking system. Disk brakes are deployed only when there are heavy loads, and then only to assist a vehicle stopping. Disk brake deployment is automatic and blends into the electric brake towards the end of the braking cycle; it isn’t something the operator has to trigger. The squealing occurs sometimes when light braking is applied—coming to a slow stop or inching through traffic in the case of streetcars.
Various other factors also contribute to brake squeal, such as moisture in the air and the condition of the disk brakes themselves. TTC vehicle engineers and maintenance staff are very much aware of the noise and its impact on passengers, pedestrians, and residents, and continually work to limit—or eliminate—brake squeal over the widest range of operating and environmental conditions possible.
The new LRVs that will begin to arrive in 2011 and the Toronto Rocket subway trains that will roll-out in a few months time will be much quieter, on a number of fronts, including brake and rail squealing, which allows me to segue nicely into a much more common complaint: rail squealing.
I won’t bore you with a physics lesson (I couldn’t if I tried), but essentially what happens on curves in the subway and on loops on streetcar lines, is a function of metal on metal friction. Fans of 80s rockers Anvil—and they are legion—will know what I’m taking about.
A fixed axle forces steel wheels on the ends of the same axle, to travel at different speeds on a curve. The outside wheel, in effect, is playing catch-up with the inner wheel on the curve. As a result, the outer wheel attempts to spin faster, thereby skipping, sliding sideways along the rail and rubbing on the corner of the rail head—generating friction, hence the unbearable squealing you sometimes hear on a curve.
And, no, there is no fear of derailment. This is a perfectly normal rail operation, albeit a potentially noisy one. So, what do we do about it?
In short: lubrication.
The TTC uses environmentally friendly grease that is automatically dispensed at strategic points along the tracks—both subway and streetcar. As a vehicle approaches a curve, it triggers an automatic dispenser that applies a sufficient amount of lubrication to the rails to lessen or eliminate, entirely, this metal on metal friction. Reservoirs embedded in the road and along tracks in tunnels, do need to be topped up and, occasionally, do run dry.
Okay, but why, you might ask, does one train run through a curve in relative silence, while the next causes even the most hardened Anvil fan to reach for their ears?
Simply put, each train and streetcar is different. Variables like speed and passenger load means the application of grease can never be precise. Dispensers are in fixed locations, and while the TTC looks for optimal placement, these variables will always be a factor in eliminating rail squeal.
The good news looking forward is the new subway trains will have a lubrication system built into each undercarriage, ensuring greater precision based on those variables as the train hits a curve. That level of detail has yet to be worked out for the new LRVs, but it is something we’re actively looking at.
Finally, steel wheels can “flatten,” which can also cause a thumping or vibration. There is a rigorous maintenance program in place at the TTC to machine rail car wheels to ensure any “flats” are eliminated, thereby lessening noise issues for both our passengers, as well as operators who ride the system day and night.

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Comments

  • http://undefined EricSmith

    The squealing occurs sometimes when light braking is applied…

    Sometimes? Subway brakes shriek more often than not. I assume that the reason comes down to money, one way or another: either the brakes sacrifice quietness for mechanical simplicity, making them cheaper, or there’s no interest in keeping the brakes sufficiently in tune to prevent noise, since that would increase maintenance cost.

    Say what you like about cars, but they sure do stop quietly compared to subways and buses.

  • http://undefined nib

    interesting. this is one of those things you come to accept but rarely question on a nuts-and-bolts level. i just always thought “metal on metal,” and didn’t realize it had so much to do with the brakes too.
    but boy, he sure, uses, a lot, of commas.

  • http://undefined Dipp

    Agreed. We should eliminate all public transit because cars are quieter.

  • http://undefined ReluctantTorontonian

    Mr. Ross handled the question with a good deal of humour and some genuine insight; I’m actually a little charmed by his writing. If all of the TTC’s riders and passengers had this sort of light hearted sincerity, then maybe squeaky wheels would be the only thing anybody would bother complaining about.

  • http://www.pragmatic.ca Greg Smith

    “A fixed axle forces steel wheels on the ends of the same axle, to travel at different speeds on a curve. The outside wheel, in effect, is playing catch-up with the inner wheel on the curve. As a result, the outer wheel attempts to spin faster, thereby skipping, sliding sideways along the rail and rubbing on the corner of the rail head—generating friction, hence the unbearable squealing you sometimes hear on a curve.”

    Allow Mr. Feynman elucidate this phenomenon:
    http://www.youtube.com/watch?v=y7h4OtFDnYE

  • http://undefined Lands Down

    If the TTC’s biggest problem was squeaky wheels maybe passengers could be able to muster up some sincere light-heartedness.
    Instead, because the TTC seems to be perpetually just managing to keep its head above water, we have this instead:
    http://www.blogto.com/city/2009/09/morning_brew_ttc_metropass_too_popular_newstalk_1010_lineup_shakeup_guns_tracked_down_teens_gang_assaulting_and_smoking_blackmarket_butts/
    http://www.blogto.com/city/2009/09/is_the_york_brt_a_waste_of_money/
    This isn’t Mr. Ross’s fault, though it is partly Mr. Giambrone’s.

  • http://undefined jcrow

    Yes, his command of basic grammar, capitalization and punctuation is quite disturbing, isn’t it?
    I think the other thing that makes the subway squealing so unpleasant is that it’s happening in a echo chamber. You’ll notice it’s not nearly as painful at above-ground stops like Old Mill.

  • http://undefined jcrow

    Your sarcasm contains a truth. I’m sure this incredibly loud squealing helps convince a lot of Torontonians that taking the TTC is unpleasant, and that driving is better.
    Anything that can be done to fix this problem would contribute immediately to a better experience, and help make the TTC more popular. Hopefully that inadvertently doesn’t help put it out of business since the TTC doesn’t seem to do so well when more people ride.

  • http://undefined bigdaddyhame

    When I was a kid we still had the PCC streetcars and Gloucester subway cars, both of which squealed long and loud when rounding corners. I miss the sound – it was a lower, rounder note than today’s vehicles produce. Still painful to the ears but less grating. Then again we also had the trolley buses which hummed and made pleasant twing-twing sounds as their trolleys hit junctions in the overhead wires. Sigh. Times (and sounds) change.
    Thank you for the Anvil reference, Brad. I enjoy this series.

  • http://www.bitpicture.com Marc Lostracco

    I’m not a fan of the screeching, but I absolutely love the low whoooooh sound of a streetcar gliding by. It’s such a signature “Toronto” sound. I kinda hope the new streetcars sound the same.

  • TokyoTuds

    Surely some of the noise on subways must be a function of the trains stopping so fast that it seems like a freakin’ emergency stop at every station. I warned my wife when we moved here from Tokyo that she should hold on tight when standing, or remain seated, until the subway comes to a full stop. The drivers in Japan are capable of coming to a gentle stop every time, so could we benefit here in Toronto from driver training to achieve this for passenger comfort?

  • http://undefined cprincipe

    Speaking of Gloucesters, I’m nostalgic for the sigh of the pneumatics just before the doors shut and the train got underway.

  • http://piorkowski.ca/ qviri

    In the next Rocket Talk: why are wheels round?

  • http://undefined EricSmith

    Everybody knows that square wheels are significantly cheaper than round ones. The TTC chooses the gold-plated circular ones because of the damned unions, Mayor Miller, and the Red Chinese.

  • http://undefined Solex

    That article, and the people who responded to it, are full of shit.

  • Scott Hazelton

    “A fixed axle forces steel wheels on the ends of the same axle, to travel at different speeds on a curve.” This question seems stupidly obvious to me, but why not add differentials on each axle rather than elaborate grease dispersing systems and a machine lathing staff to round off wheels?