This is wrong. Lower frequencies contain more energy (much more!), and the "screechy" noises from buses and trains are instantaneous and not likely to cause any long-term damage unless your exposure levels are absurd (like working at a bus garage). That "painful" spectrum is a lot lower than you're thinking it is. Try 18khz out on a tone generator some time; IF you can even hear it, it's a lot different than the noise of a brake squealer or hydraulic pump. It also really doesn't matter what kind of noise you're being exposed to; noise is noise, and if it's too intense it can damage your hearing (doesn't matter if it's a rock concert or a machine gun). What kills your hearing is exposure level over time; not frequency (and yes, noise-induced loss can be narrow-band depending on what you're doing). Finally, listening to music on the street and so-on only works if you have isolating IEMs, otherwise you're doing something known as "blocking" where you're cranking the music up to drown out the background noise - this is the worst possible thing you can do, and is one of the biggest reasons that modern research supports noise-induced hearing-loss being very prevalent in younger listeners; all those crazy kids blasting their iBuds at 150% just to hear the lyrics. Using high-isolation IEMs or headphones while walking around on a busy street is not advisable, as it decreases your awareness, and makes you a better target for things like cars.
As far as what I do: I picked up a pair of Etyplugs this last winter for use with some yard equipment, and ended up just taking them with me everywhere I go (They even included a little pouch). I've found them nice for traveling around mostly to cut down annoying noises (rattles and clicks from riding on the train), but I'm skeptical that I'm really "saving" my hearing or anything (because again, the exposure level/time that I'm dealing with is so minimal). Since all they do is provide ~12 dB of broadband attenuation, but add no music, I can still pay attention everything around me, it's just about half as loud. I would never take something like my Leight L3's out on the street though (NPR of 30 - you can put them on and have your buddy shout their lungs out and hear almost none of it; good luck hearing the train/bus/car/motorcycle/helicopter/transformer/gundam/samurai coming up behind you - great for when you're running a snow thrower or shooting though).
For those interested:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735
http://www.ccohs.ca/oshanswers/phys_agents/exposure_can.html
The simple answer to avoiding hearing loss is to reduce exposure. Think about it like radiation. The quantities needed to kill you instantly are extremely high, and not generally found outside of specialized industrial environments. However, if you are exposed to a lesser but "accessible" amount over time, it can do the same damage. In other words, sure - standing right behind a 747 or F14 as it takes off will probably destroy your hearing in a single pass (assuming it doesn't kill you in the process), but you probably aren't going to be able to do that. However, listening to your music at 90-100 dB for a few hours every day, over a few months or years, will have the same effect. You will naturally lose HF as you age, and many older people (say, late 20s or more) usually cannot hear up there at 18k or 16k or whatever else at the same level - that's natural (the 20-20k average is a very generalized statement; the bottom end is just as inexact).
Also remember when selecting hearing protection, it may not be broadband. It probably isn't (LF is very hard to attenuate because it contains so much energy; the only real way to kill LF is with mass, LOTS of mass - that's hard to do with a hearing protector).
I'd still like to see some proof of this. Then you go on to say what damages your hearing is noise, not frequency... you just said a lower frequency wave carries more energy (not right, but let's think so). More energy means more pressure, thus more damage, so frequency makes the damage be more or less effective. And because I can't hear a 18kHz it won't harm me? I guess I can go to Chernobyl and not die of cancer because I can't see the radiation. Kids, if you're reading this, do not play with high frequencies.
