Nearly all the freeways in Phoenix now have rubberized asphalt overlays, but years ago, the grooves in the concrete were perpendicular to the direction of travel and they made a whistling sound that was quite a bit louder than the "clunk-clunk-clunk" of L.A. freeways.
I remember when the freeways in phoenix made that wonderful whistling noise. Although rubberized asphalt is nice, I really miss that sound. It always sounded so cool when getting on or off the freeway, hearing the changing pitch.
It's too bad that it's almost nonexistent now in Phoenix.
I've noticed that some freeways are starting to get the "clunk-clunk-clunk" sound. For example the northwest corner of Loop 101 around union hills.
When I was a kid, I loved going with my parents or grandparents and driving on the freeways. That high pitched whistle was an awesome sound. For my younger sister, however, it was instantaneous in making her fall asleep. If she was fussy and wouldn't take her nap, just jump on the Superstition for a couple miles and come back. Bam, she was out.