Don't walk,take an uber. Or 🚕 perhaps. You can walk But it will take 20 minutes or so. And there are not anymore sidewalks between these terminals and the observation deck.
You could walk, it would be a long walk and you wouldn't have a sidewalk.
It is drivable front either terminal, therefore I assume you could walk on the side of the road, etc. I don't recall one way or another if there was a sidewalk, etc. A park-and-ride bus may go between the terminal & a parking lot near the observation deck. Sorry I can't be of more help with your question.
I wouldn't recommend it. Maybe catch a shuttle if it will stop but no, walking
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