When approaching a tollbooth, look for signs and signals that indicate which lane you need to be in - a green light indicates which lanes are

A green light indicates which lines are open.

Explanation:

When approaching a tollbooth on a freeway one should always look ahead for signs. The driver should also slow down in advance because he might need to change lanes rapidly. The lane one uses should always be the one designated for the specific types of vehicles ( some lanes are for buses or trucks only).

One should only use lanes with green lights or signs above them as they are marked as open. Closed lanes are marked as red.

b) to encourage free trade

the answer to your question is,

old stone age.

-mabel < 3