What do people do when they have really important jobs and must get in but the weather is bad?

I work for the government, in a mid-level job, and when the weather is bad, I just call in and use a day (vacation day, personal day, whatever). My coworkers do the same. Today it’s below freezing and there’s an ice storm, so a lot of us are home again (after a few snowstorms in the past few weeks). However, I know there are people in the private sector who have jobs where they are expected in to work unless it’s really terrible out.

How do these people do it? How do you get to work if it’s bad out and you are obligated to show up?