How Loud Is That Bus Outside My Window?

How loud is that diesel (or natural gas) city bus?  Too loud: about 93 decibels (peak volume) measured from a bus stop when the bus is pulling away from the curb.  On the sound scale, that is more than four times louder than a vacuum cleaner (70dB) and more than twice as loud as an alarm clock (80dB).    That makes the MBTA’s city bus Boston’s noisiest neighbor.  No wonder why people have a hard time adapting to living near a bus stop.  Just don’t open the windows.

The only thing louder?  Interestingly, riding in the back seat of the bus is as much as four times louder than staying at the stop.  My handy Radio Shack meter clocked a very impressive 112dB (peak volume) when the bus was accelerating at moderate to high speeds.  That puts riding on the back seat of the bus on par with … sandblasting or attending a loud rock concert!  Better change seats after 15 to 30 minutes; sitting in that back seat much longer could exceed OSHA’s daily permissible noise level exposure.  Incredibly, standing ten feet away from an MBCR locomotive accelerating through an underpass did not beat that peak from the interior of the bus, although the locomotive may have sustained a higher average noise level.

It probably would not exaggerate much to guess that the MBTA’s diesel and natural gas bus fleet has become Boston’s de facto alarm clock.   Of course, it didn’t have to be that way.  Years ago, the diesels replaced whisper-soft trackless trolleys.  Trolleys of the trackless variety still operate through Harvard Square on overhead lines, and still barely make a sound over the background traffic.  Sure beats having a double-volume alarm clock for a neighbor.

5 thoughts on “How Loud Is That Bus Outside My Window?

  1. Yes, the MBTA’s buses and MBCR’s diesel operations are both loud and polluting. I recently moved to Boston from New York after having lived on various parts of Long Island for most of my life until I moved up to Troy for college.

    With that, it became glaringly apparent how noisy, slow, and unreliable commuter rail operations are in the area, having come from an area served by one of the original commuter railroads who electrified their lines in the early 1900s and have benefited from those investments in terms of operational reliability, air quality, and noise pollution.

    Something I never got to see in the City during my residency there was the recent introduction of a set of turbine hybrid-electric buses to the MTA Buses fleet ( These buses literally run silent (as silent as the electric trolley buses that still run between Watertown, Somerville, and Cambridge) when its batteries are charged. When the charge becomes low, the turbine engine kicks in and merely serves as an electric generator, so the engine doesn’t rev up when the bus accelerates. I commented on the use of these in the system to MassDOT in regard to the recently acquired hybrid bendy buses, funded by an ARRA grant:

    As Ben mentions over at the SAS blog, NYCTA is still in the process of doing structural testing, but there’s a wealth of HD YouTube videos available by people who have gone bus fanning for these buses. I’ll probably get one of those nifty meters and bus fan myself next time I’m in the City and post my results on my blog.

  2. I must say, the trackless trolleys are far from silent — especially inside. At least they don’t sound like a fighter jet taking off.

    I remember the old ones (eliminated about 6 years ago) made this wailing noise that could be heard for a mile. Loved those.

  3. I work on Huron Ave and while I love the quiet electric trolleys I’m floored by how loud buses are – trucks too for that matter. It really makes it unpleasant to be anywhere near the street. Even inside, with windows closed, the roar can be overpowering. Do our ears get more sensitive as we get older or are vehicles much louder nowadays?

  4. Which model of bus are your measurements for? The sounds coming from each model of T bus are very different.

    I love the New Flyers, since they have great acceleration. But they are rather loud, especially in the lower frequencies.

    The NABI CNGs make a lot of noise as well. A few of them make unusual noises that could indicate problems, like a high-pitched whistle coming from the exhaust.

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