One year ago after seeing a horrible bridge collision I decided to
investigate low clearance avoidance tools. After a great deal of
searching, by far the most cost effective solution was to
download a low clearance POI database for my GPS.
There were a few free ones out there to download but they were
very limited in size (around 300 - 500) which isn't much use so I
figured I would risk 20 bucks and get a professionally made one
which had over 3000 low clearance alerts.
I've been so impressed with it that I made several positive
comments on quite a few forums in the hope that other drivers
will follow suit and avoid these potentially fatal accidents.
If you're interested (and you really should be) you can get it from
http://www.lowclearances.com . I use a Garmin but you can also
install it on MS Streets & Trips, Delorme Street Atlas,
Google Earth, TomTom, and Navman.
Safe driving.