In principal right.
It would be sufficient to tune to any radio station (not necessarily the strongest) which signals TA capabilities. Probably it could be done by auto-tuning one station up, wait for RDS and the TA signalisation (30sec or so), if not present tune up to the next station.

The TA signal is not to be mixed up with an Traffic Announcement. The TA signal just informs that the radio station gives frequent traffic announcements. So I would not wait for the announcement, but for the RDS flag that tells me that there will be an announcement.

Juergen