It's good for any toll road in MD... and it worked for me on a drive from Baltimore to Philadelphia... even in Delaware and New Jersey... I think it's a transit region maybe.. but I would definitely double check that the signs are purple and say E-Z Pass before you drive through a toll area without stopping to pay.
You can use it anywhere the only thing is that you will not get the discount for the particular state. You will just pay the regular fee.
No. Only in certain states.
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