Easy, if your iPod Shuffle doesn't have a sound level indicator, you simple can't use it. Again, everything has rules, and you would need to be required to have a MP3 player to have sound levels. Another idea is a specific brand of MP3 set by company standards that is the only thing you can use.
Driving a go-cart, golf shuttle, a large truck, boat, any of these things that have wheels or riding on water, including forklifts, ARE the same. They all come with the same hazards.. its just forklifts have FEWER hazards than most. Outside you have weather to deal with as well.
Yet another case in point. Do you honestly think deaf people aren't allowed to drive cars? Or get on a forklift? (Not all night, he would have to hear the calls on the overhead to actually work the job in our facility haha.) And I would NOT want a stereo on any of the machines at our facility. Not only would that be annoying to people around that person... although playing something funny while driving around would be comical... but it would be a distraction when everyone has their stereo on listening to different things at once. That is why you don't see a forklift with stereo's, there's no way to seal in the sound.
So in a nutshell, you agree people in cars listening to their radio are not distracted, but.. you think just because you're on a forklift listening to music changes that? That safetydan, is being a hypocrite. =\
Myself, having drove/driving a forklift, is just like driving a car, except I can do cool things like move other machines out of my way if they block my way, traffic-no-more machine go!! =)
Sorry to hear you can't chew gum and work at the sametime...