Mathematically, How Does This Work?

Here is the headline from today's Washingtonian:

DC Will Lower Its Default Speed Limit to 20 MPH

Some streets, where more space is needed for social distancing, will be lowered to 15 MPH

Faster speeds require more distance between cars for safety.  Slower speeds allow cars to be closer together.  How does so-called social distancing even work with cars?

Coronavirus foolishness.