I accidentally tagged my Clipper card twice on Caltrain. Will I be charged twice?
It depends. If the second Clipper Card was tagged at the same Caltrain station within 15 minutes of the first tag, the second tag will cancel your ride.
The Clipper card reader will show a message that your initial Clipper Card tag was refunded. If you want to ride Caltrain, you will need to tag on again.
If your second tag was done after 15 minutes, you will be charged the maximum one-way fare.