The expression, “safe travels” is used when someone you know, such as a friend or relative is going on a trip. It might be used when they are going on vacation or traveling for work. But it can also be used when someone is traveling for a shorter distance, such as driving home from a party. In short, it can be correctly used at any time that someone will be traveling, by whatever means.
“Safe travels” is used as a way to express your wish for someone to have good fortune during a trip. When you say, “safe travels,” you are expressing that you hope someone’s journey goes well. It is used in a similar fashion to another commonly used expression, “good luck.” It can serve as a reminder to drive carefully as much as anything else. But it is also used to express your hope that nothing goes wrong while they are on the road or in the air.
As an example, imagine that your sister is flying to California to visit her boyfriend. She says goodbye to you, and as you help her load her suitcases into the taxi she will take to the airport, you might then say, “Safe travels.”
Imagine another scenario in which the phrase may be used. You are driving from Nashville to Chicago for a work conference. Your spouse kisses you goodbye, and then says, “Safe travels.”
Some other ways of expressing the same sentiment include: “be safe,” “stay safe,” and “drive carefully.”