.... does anybody know what are the exact rules on salting roads in Vancouver?
I don't know if there are rules, but they'll dump the salt down when it's completely DRY out, as long as the dew point is within reach.
If you park on the street, even if you don't drive, your Bus will ROT out. The salt trucks will spray it. The best is to scope out an alley to park in, the salt trucks don't do the alleys.
At the first sight of grey roads, they've sprayed the roads. If you can walk to the grocery store, you can avoid driving. If there are transit busses, it's worth it to ride with the weirdos (entertaining too).
Last winter my car saw ZERO salt. We didn't have a lot of below freezing days, and I was able to avoid all the salty days. I give it a day or two of rain to wash away the salt, then I'll drive. The vast majority of the rain drains away and takes the salt with it. I believe it doesn't take much to completely clean away all the salt. Once it's disolved, it's down the drains.
If you live in an apt that has a car wash area, give it plenty of rinses if you get caught out in the salt.