The one time I tried to use it at the airport there was a lot of confusion. Might be better now but I just use license or passport.
@ET:
Most airports use a nationally recognized security system dedicated to airport security to monitor people in controlled areas. In some ways it's more difficult and time consuming to get than a TWIC card.
The TWIC was started to control background checks on people having access to waterways that had access to open waters (Pacific and Atlantic oceans, Gulf of Mexico and Great Lakes. It was rapidly converted to use by our refinery system to monitor contractor access to work areas within the refinery. Never really caught on in the gas plant industry.
It is a good form of ID and accepted without question where it's recognized. Keep in mind that it's a government program so obtaining the card may take some effort and rework. The system does contain numerous glitches that may result in reapplication.
If you have one, renew it on time. Expiration lengthens to renewal process. 4951