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.