Tuesday, March 10, 2015

Killing Them (Not So) Softly: BART and Your Eardrums

For anyone who has taken the BART in San Francisco, and for anyone who takes it every day, you know that these trains are loud. Like, really loud. In fact, if I didn't have my in-ear headphones, I would have to cover my ears through some sections.
For my own sake, I needed to know whether taking the BART would affect my hearing over the long term.
(Image: Wikicommons)

But just how loud is it?

I decided to finally check with a decibel counter app. While it is not an officially calibrated decibel meter, in practice I've found it to be fairly accurate in terms of measuring ambient noise and relative loudness thresholds.

I took my measurements in one portion of my daily commute — the area between Balboa Park and Glen Park — representing one of the loud underground tunnel areas. While most of the SF/Peninsula BART is underground, speeds can vary. As you can guess, the faster the train goes, the louder it generally becomes.

Thanks to Sound Meter, I now know something I already knew. BART is freaking loud.
These are my results, in motion GIF form. You can see that the range extended from 48, which actually is rather quiet, all the way to 83. Also important is the fact that decibels are a logarithmic scale, which means that a change of 10 decibels reflects a change in the power of 10. So if my math is correct, the peak recorded value of 83dB is approximately 3,160 times louder than the ambient noise of 48dB

Here are some additional details:
I think the PA is extra loud to accommodate elderly or hearing-impaired riders. That might be most of us soon.

You can see the dip during a brief loss of acceleration, then a steady grind down to ambient levels.

That leads us to what my findings actually mean in terms of hearing. According to the National Institutes of Health:
Sounds of less than 75 decibels, even after long exposure, are unlikely to cause hearing loss. However, long or repeated exposure to sounds at or above 85 decibels can cause hearing loss.
So we're in this gray area of 75-85 dB where it might be dangerous. But remember, with 83dB, we got pretty darn close to that 85dB limit. And even though our BART rides don't really qualify as "prolonged" exposure, it does make more sensitive ears (like mine) hurt. And frankly, that's enough for me.

To be fair, humans need some level of ambient noise. It's actually very hard for a healthy human to suddenly be deprived of all noise. In fact, they tested it with the world's quietest room and the longest anyone lasted was apparently only 45 minutes. But we're not talking about too little noise. We're talking about too much of it.

According to NIH, up to 15% of adults 20-69 already have a measurable degree of hearing loss. So whether that's caused by occupational hazards, listening to loud music, or riding the BART, I'm really in no hurry to get my ears fitted at my local Costco for a set of hearing aids any time soon. If you ride the BART, it may be helpful to bring along some earplugs or noise-blocking earphones, just to be safe.


  1. Very nice field scientific work Andrew. Your analysis is sound !


  2. Thanks for reading, Randy! I'm going to run the same test the next time I'm on an airplane. Now THAT's definitely going to qualify as "prolonged exposure".

  3. Ear phones or ear plugs help but you can still hear a train with bad wheels loud and clear right on through the loudest of music. I don't know how BART's Train Operators put up with this on a daily basis. I applaud them because it is nasty coming from Colma, through the tube at certain spots, Oakland. It's a joke. BART works on these tracks supposedly non-stop and the tracks are still all screechy and noisey. They spent $19 million on a track grinder I have yet to see produce any noticeable results. What does improve the situation is new wheels on the train cars. In the old days, BART was never delayed over track maintenance for weeks and years at a time. Can the passenger ever expect a normal to and from San Francisco commute any more? Time for a new Board of Directors and new BART Management. The current Board has destroyed BART's infrastructure and have spent all the resources on unfinished projects and giving themselves 7.2% raises when they provide service to passengers that is TOTALLY DEPLORBABLE and inhumane, not to mention filthy and unhealthy. YEAH YOU GO BART; go to Satan's den where you belong. .

  4. You have to exceed 85 db to pose a health hazard. I base this on the astm 963 toy safety standard as that one has pretty strict standards for childrens products. Although, i've hit 94db "A" weighted on some parts of the system.