Why not contoured more like a sound testing room What exactly to you mean by "contoured"? If you're referring to the large wedges you see in anechoic chambers

Why not contoured more like a sound testing room What exactly to you mean by "contoured"? If you're referring to the large wedges you see in anechoic chambers or foam panels you might see in recording studios, those are absorption panels using soft porous materials that absorption high frequency (small wavelength) acoustical waves that cause problems in those environments. For outdoor barriers, most of the sound attenuation is achieved by blocking the line-of-sight between the source and receiver, and forcing sound waves to take a longer path around the obstacles. You do occasionally see absorption used in outdoor barriers to absorb mid and high frequencies, but generally those in the form of perforated metal panel absorbers or porous spray-on materials like Pyrok. Soft absorbers can;t be used since the wouldn't hold up to the outdoor elements for very long. There have been experimental walls constructed with various horizontal and vertical geometries to try to achieve better reduces for a given wall height. What they found is that they are able to get slightly better performance (and by slightly I mean 0.1 dB to maybe 1 dB) with things like non-linear walls and rounded caps, but the extra cost involved didn't justify the performance increase. I've often wondered if you could efficiently capture usable energy from motorway noise. Going from electricity to sound (like a loudspeaker) or vice-versa (like a microphone) is extremely inefficient. The impedance mismatch between the moving air and the transducer is too much to overcome with current tech.