Subway noise and vibration
Facts about some of the causes and how we are working to manage it
We recognize that transit activities from our existing operations produce noise and vibration, which may affect our neighbours.
The TTC understands the importance of being a good neighbour. We also recognize that as the city continues to grow and evolve, new development continues to encroach upon our facilities and right-of-ways. Although growth in the city is facilitated by the availability of high-quality transit, it also exposes a greater number of people to transit-related noise and vibration.
TTC operational practices and maintenance procedures have been developed, that aim to reduce operational noise and vibration. Whenever possible, technologies are employed to reduce noise and vibration when new vehicles are purchased and extensions are built to the subway system.
Discussed below are some of the transit-related noise and vibration issues that are particularly difficult for the TTC, and all transit agencies around the world, to completely eliminate.
Wheel squeal from rail transit operations is a common occurrence on rail lines around the world. TTC subway operations also produce wheel squeal. The frequency of this squeal noise can be a source of annoyance to our customers and to residents who live adjacent to our rail operations. The sensation of a frequency is commonly referred to as the pitch of a sound. People generally refer to the “high pitch” of the squeal.
Wheel squeal is caused by the steel wheel interacting with the top of steel rail and also by the interaction of the wheel’s flange with the side of the running and restraining rails. Most commonly, this squeal/screech occurs on curved sections of subway track. On some portions of the subway system, such as the curved tracks approaching Union Station, automatic wayside lubricators are used, and a specially formulated lubricant is applied to the side of the rails. The lubricators help to reduce noise levels but do not entirely eliminate the squealing sound. The lubricators are inspected regularly by track maintenance staff to ensure they are operating properly. However, from time to time, humidity levels and sudden temperature changes can reduce the effectiveness of the wayside lubricators.
Ground-borne vibration can be a concern for residents adjacent to the older portions of the TTC subway system, such as Line 2 (Bloor-Danforth). Annoyance from vibration often occurs when the vibration exceeds the threshold of perception by only a small margin. The effects of ground-borne vibration include perceivable movement of the building floors, rattling of windows, shaking of items on shelves, and rumbling sounds.
The TTC uses technologies similar to the ones used by other transit systems around the world to minimize vibration. These measures include: continuously welded rail, resilient rail fasteners, floating slabs and ballast mats.
The low-frequency rumbling noise that some people may hear if they live adjacent to the older portion of the subway system is created by ground-borne vibration. The vibration results in noise being radiated from the motion of the room surfaces. In essence, the room surfaces act like a giant loudspeaker causing what is called ground-borne noise. The level of these rumble noises varies widely from house to house and is very dependent on the size and design of the home, and also on the type of soil that the home was built on.
In 1978, the TTC introduced a double-tie discontinuous floating slab design for the Spadina Subway Extension. The design involves fastening rails to concrete slabs, which float on large rubber disks. The design has been very successful in reducing rumbling noise. Converting the older portions of the subway to a floating slab configuration is not feasible, practically or economically and would require the subway system to be shut down while reconstruction takes place.
The TTC’s steel rails act as electrical circuits that form part of the existing train signalling system. These circuits allow our signal system to know where a train is at any given time. The boundary between two circuits in the track is called the insulated joint and when a train passes over the joint it produces what many people refer to as a “clickety-clack” noise. Over time, this joint tends to wear and the clickety-clack noise increases. Although the noise cannot be completely eliminated, the TTC maintains the joints in a state-of-good repair on an on-going basis.
The TTC is currently replacing its aging signal system with a modern system that does not rely on insulated joints. However, the existing signalling system will be maintained for some time to come. For this reason, the insulated joints will be in place for many years.
The clickety-clack noise can also be heard at special track sections, such as switches and cross-overs where gaps in the rail exist to allow switches and rail to move. Unfortunately, due to the severe temperature fluctuations that occur in summer and winter, the gaps are designed to allow for thermal expansion of the metal rail. These rail gaps cannot be eliminated.
In order to prevent injuries and fatalities, the TTC’s strict operational safety rules require that subway train operators use their train horns under several safety-critical conditions. As one example, when maintenance crews are working at track level, a train operator is required to use the train horn to acknowledge the crew’s hand signal, such as a signal to the train operator to reduce speed. The train operator will acknowledge the signal through one short blast of the train horn. Given their safety-critical nature, there are no time restrictions on the use of the train horns. The safety rules must be followed at all times.
Noise Abatement – Subway Car Equipment
Wheel Flats and Wheel Roughness
A wheel flat is a flat on the surface of a steel wheel. Flat spots create levels of noise and vibration that can be annoying to neighbouring residents. People often refer to the sound as a “thumping noise”.
Flat spots are more common in the autumn and winter when wet leaves fall on the rails or when it rains and/or snows. The rain and/or wet leaves can make the top of the rail “slippery” and when the subway train brakes, it can cause the subway car wheel to slide along the rail after the wheel/axle has stopped rotating. This sliding can grind a flat spot on the wheel.
Flat spots can also be caused by the activation of the train’s emergency brake which, in some instances, can cause the wheel(s) to lock up and slide along the rail causing a wheel flat.
The TTC has installed remote monitors on the subway line to measure the condition of wheels of in-service trains. These monitors allow us to identify and measure the severity of the wheel conditions of subway cars as they travel past the monitoring station. TTC crews schedule wheels for wheel truing as soon as practically possible to keep wheel flats to a minimum.
Subway car wheels and rail can also develop irregularities (“roughness”) over their service life. Rail grinding equipment is used to smooth rough sections of track and wheel truing is used to smooth a subway car’s steel wheels.
In order to remove a wheel flat, a subway car must be placed on a special machine called a wheel lathe (or wheel truing machine). The machine cuts out the flat defect and makes the wheel round again. The TTC has three wheel truing machines and operates them at full capacity.
Over time, irregularities develop in the surface of subway rails. This normal “wear and tear” increases noise and vibration levels, both for our customers and also for the adjacent community. Rail corrugation is one such defect. To return the rail to its standard operating condition, an operation called rail grinding takes place. This activity involves dragging large heavy stones along the rail. The procedure is noisy – and by necessity for safety – must be carried out in the early hours of the morning after regular passenger service has ended. Whenever possible, the TTC provides the community advance notice when rail grinding has been scheduled for a specific section of the subway system.
New Development Adjacent TTC Operations
When a new development is proposed within 60 metres of our rail right-of-way, the TTC requires that developers incorporate noise and vibration mitigation into their designs. The TTC also requires that developers advise prospective purchasers and lessees, through a clause in the purchase/rental agreements and in condominium documentation, of the potential for noise and vibration and that the TTC accepts no responsibility for any such effects.
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