You are not late if they know you are late.
Think about that the next time you are going to be late at a meeting. Most of the times you are late you actually know you are going to be late way in advance. But you deny it, try to avoid it and then do it anyway.
But you will find out that if you call, even if it is only 10 minutes in advance, that you might not make it people will hugely appreciate that.
So, the next time you have a meeting and you think you might not make it in time pick...