A lot of cyclists have a sticker on their bikes that says “One Less Car.” I fully support the sentiment, but the grammar sucks. It should say “One Fewer Car” or “One Car Fewer.” Why?
You use “fewer” when talking about things you can count, like bicycles or people or cars or traffic accidents.
You use “less” when talking about a quantity of something that cannot be counted, like sugar or happiness or guilt or rain.
“Less” is more commonly misused than “fewer.” These are incorrect:
More bicycles means less cars.
There have been a lot less accidents since they put in speed bumps.
There’s been a lot less people coming by the store today.
You can sometimes use “less” with countable items if those items together form a unit, like “less than ten feet”– the ten feet are not ten separate countable items, but one unit. Similarly, you would say something cost “less than five dollars.”
If you see someone hovering around a bike rack with a Sharpie, that’s me.