They're not? Over here, periodic car inspections are mandatory. New car models can't be sold until they've been checked and found to be compliant with various regulations, presumably including loudness. I guess there will always be "car enthusiasts" who think that LoUD pIpEs sAvE LiVeS (they don't), but I don't see/hear heavily tuned cars anywhere near as often as in the early 2000s.
Many people just revert the modifications in order to pass the regular inspection. And enforcing is hard logistically because the Police should be able to detect and confirm such cases. Which means personnel, training, equipment, and a lot of time taken away from other duties. This won't deter anyone from tearing up the asphalt in an area that appears to have no police around.
Not if they are driven on european roads. Any car made after 2018 (??) can't have them. I know mercedes AMG plays an modified/amplified sound inside the car, but the new regulations in the EU forbids any new car from having this.
There has been talk about a labelling similar to environmental zones (which means older, dirty exhaust cars can't drive in cities) as well, meaning loud cars would not be allowed in cities.
Edit: oh, and everything louder than 72db, 0.5m from the exhaust at a 45degree offset, is already forbidden for cars iirc.
Pipes can give a car a cool sound. But most people like music too. But they sure don't like it blasted at all hours of the day and night at random intervals.
Even for cars, there's also the issue of how the noise measured, compared to the real-world use. And even for motorcycles, that are standards, and even if there's no mandatory regular inspection, police are allowed to control vehicles randomly. But they practically never do it for some reason.
I'm familiar with the measuring method for motorcycles, which basically means that a powerful enough motorcycle will be very quiet when tested because it will be running at very low RPMs (the standard is 3rd gear at 50 Km/h – on my bike that's around 1500-2000 RPM out of 10000).
The noise issue is with people flooring it just to stop at the next light 200 m down the road. And also badly tuned exhausts that pop like crazy.
I'm actually wondering if this hasn't become a fashion for some reason, since I hear more and more cars make that noise. And those cars look pretty expensive, so I don't think they have aftermarket exhausts, if only because changing it is a bit more involved than on motorcycles, and pretty much all newish-looking "fast" cars seem to make that noise.
But I agree, in Paris at least, loud motorcycles are more of a nuisance than cars, if only because there's more of them. Cars do tend to get on my nerves on weekends, though.
"Loud pipes save lives" was a popular slogan on bumper stickers on obnoxiously loud cars for a good while. It completely ignores the fact that loud pipes wake people up, which shortens lives, or that it increases stress in people and animals alike.
Probably just the fact that pedestrians and other cars can hear you coming if you have loud pipes.
Motorcycles in particular have the danger that if a driver in a vehicle doesn't see them, they can get ran over. Being smaller, they have a tendency to easily hide in blind spots or just not be noticed at all because the driver is expecting another large vehicle.
So many motorcycle riders use flashing headlights and loud pipes to announce their presence.