The "big brother" concern is that it is possible to read the toll tags without causing them to beep; this is used (without charging any tolls) to give live traffic speed reports like on
http://www.sigalert.com . People worried about "big brother" type uses of such toll tag reading would want to put the toll tag in an RF-proof container at times other than when passing through a toll booth (FasTrak gives, or used to give, supposedly RF-proof bags with the toll tags to make such people more comfortable having it).
With the quality of image recognition cameras this happens in the UK without a pass. They just read the licence plate by camera. Track when you pass the next camera and discard it. Look at trafficmaster in the UK
http://www.trafficmaster.co.uk/home.php
and a link so you can see what they look like. They are not used for speed detection rather speed monitoring for traffic flow.
http://www.ukspeedcameras.co.uk/guid...affic%20Master