Hood traffic speed
I've also had a look in objectscripts, overrides, effects - and they're not mentioned. Actually - the package in effects looked to me totally unreadable.
If you could either link me to the default replacement, or send it to me - it may have enough info in it for me to track down the other infos.
My gut feel (which is often wrong) is that it is either linked to a script/bhav/str/anim or it is hard-coded. Unfortunately I don't know much about hood deco, so it will require some research.
Apart from from the tracks in the neighborhood.ini and stuff in effects.package which baffles me.
Which is not surprising because I'm not familiar with a lot of what goes on in the game outside of objects.