Think the button is for “Traffic master”. The system monitors traffic flows to warn you of hold ups ahead. I only got this info by googling and have no experience of it myself.
Wow, there's a blast from the past, I'd forgotten all about Traffic Master. It used to come as standard on Vauxhalls in the 1990s. The system was apparently retired in June 2012, according to
Honest John, presumably superseded by newer technologies. I'd offer that button to a transport museum.
