My work earplugs aren't rated for super high decibels, but they're a step up from the disposable ones most folks I work with use. They're definitely a solid step up from what most folks are going to buy from the hardware store. I've got coworkers who can converse loudly enough that I can make out the entire conversation over the normal shop noise the earplugs are supposed to be for while 200 feet away and within an enclosed (but not particularly thick-walled) office.
Earplugs will dull the noise, but if I can't take a nap over two guys having a conversation at that distance, I really doubt most folks' ability to get a good night's sleep over truck horns. The earplugs will probably mitigate the physical damage done by the noise, but I highly doubt they do much for the psychological stress. People lose their ability to focus and sometimes their sanity due to injuries that cause a constant ringing in their ears. Even if you can reduce the volume, the constant noise is a type of torture.
Edit: Found the Noise Reduction Rating for a number of different types of hearing pro that I've used in the past. The best one was rated at 33, meaning it roughly reduces the noise by something like 33 decibels. That pair, of course, being the ubiquitous neon yellow 3M product with flames on the sides for enhanced performance. I don't wear them myself because while they're fashionable, they're incredibly uncomfortable for me. This also appears to be among the best non-powered hearing pro that's available on the market. They will take an uncomfortably loud worksite at 105 dB down to effectively under 80 dB and more-or-less within a safe range for hearing. Not a pleasant level for sleeping though, by any means, although I can pull it off myself if I'm tired enough. When you start talking about a truck horn which those earplugs might or might not be able to quiet down close to the level of that 105 dB you'd experience with no hearing pro on a worksite, you're past potential hearing damage and well into a range where there is no reasonable escape from the barrage of sound.
Edit 2: Most of these earplugs in the 25-33 NRR range are definitely available at the hardware store if anyone needs to know that. They're more expensive per pair and seem to come in higher count containers, but they're there and much cheaper than the doctor's visits and hearing aids will be in the future. If you find yourself in a situation where the background noise is uncomfortable at all, please, please, get yourself some if at all feasible. Half the old dudes I've worked with in my life did not think it was worth the hassle and I'm tired of having to scream in people's ears to communicate. Also all the near misses because you have to either throw something at them or close the distance if you see a dangerous situation they don't and need to warn them.