Here's the deal on fewer and less:
Use fewer when emphasizing individual items -- that is, when dealing with a number that creates a mental image.
Use less when talking about bulk quantities (e.g. wheat) or degree.
In the case above, you can wrap your mind around the number of people representing the reduction in travel, so go with fewer.
An easier test: "Less people" sounds wrong, doesn't it? Please tell Mr. Rewrite it does. If not, send a complaint to your English teachers and parents.
Follow these links to see how many more articles on Google News go with fewer people than less people. That's usually a good guide.
It's worth noting that the organization posting the tweet above later corrected it, just as Mr. Rewrite amended this post about 10,000 times to remove embarrassing errors.
Mr. Rewrite finds he has fewer hours in the day for blogging, but he's going to try to keep this up.