I live on an artery/thoroughfare in SF. My street also has a 10-15' retaining wall along one side that faces a small valley on the other. The noise on my street is extremely loud and echoes throughout the whole neighborhood. My favorite days and nights are Sundays when streets are the quietest. Here's how I've ordered the worst offenders in my head.

1) Harley's with open pipes 2) cars without any exhaust (common) 3) after market exhaust on import cars (thanks Fast & Furious) 4) garbage trucks, gas powered gardening equipment, 4x4's/big trucks, new muscle cars 5) scooters, mopeds, gas powered bicycles, motocross motorcycles (I get sideshows/giant groups driving up/down my street to the next location), enduro & regular motorcycles

The thing is is that there are already laws in place to deal with most of those..