I just arrived at the airport and was taking a shuttle to my car.
Why did you take the shuttle? Can you explain that one to me?
Because of heavy traffic and of course I am too tired to walk all the way to my car.
From time to time everyone gets too tired to want to do something they can solve with convenience. It makes sense that you would take the shuttle to your car.
If I didn't take the shuttle I would definitely be late, I needed to find the fastest way to get to my car.
You don't have to keep explaining yourself, I understand completely now why you took the shuttle. It is valid to sometimes feel tired, and it is understandable that this would make you take the quicker and easier option.