What does "additional people" mean?

[Davy07]

Shuttle Bus is approximately $15 (one person), additional people $2.

So what does "additional people" mean?

TY
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Only the Paranoid Survive

[Harry_Ph]

Shuttle Bus is approximately $15 (one person), additional people $2 。
So what does "additional people" mean?

It seems to me that it costs $15 per person to ride a shuttle bus for a certain number of people in a group (for example, 20 people). The rest of the people in the group will have to pay $2 only.
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The more we learn, the less we seem to know.