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

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 [email protected]!

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.