Was in Boston a few weekends ago, and our (decent Garmin) GPS system would lose it's signal with about 200 feet to go in each tunnel, and then would take 1-2 minutes to reconfigure itself which was typically too late to help us make the right exit. It was frustrating to say the least to have to memorize the route 4-5 steps ahead each and every time we entered a tunnel just in case it got confused (which is did early and often)

Why can't the unit 'remember' the route in case signal is lost or have some sort of 'tunnel' recognition mode to account for this? It's not like the 'Big Dig' is an obscure set of tunnels (or Boston an uncommon city) that just 'popped up' without warning.

/rant