The actor, who plays unpopular marketing man Pete Campbell in the hit TV drama, gave up his own car four years ago after a major malfunction and he hasn't bought a replacement.
And now he has pledged not to get into another motor - and take the bus and train to work instead.
He says, "I found that it enriched my life... to slow down a little bit and walk through this city (Los Angeles) and interact with people that I usually kind of speed by on the freeway.
"It does a lot for me, other than just save me money."
And that's not all Kartheiser is doing in a bid to save the planet: "I've been a vegetarian for four years and I've chosen not to have children... which are both green choices in my life. I also xeriscaped my lawn (planted drought resistant shrubs).
"What I've done isn't miraculous; it's nothing that anyone out there couldn't do."