I fall into the "cheapskate" category, plus I don't necessarily trust the GPS systems.  I've heard of too many folks getting routed the wrong way and into questionable places.  I am old school in that we have a Trucker's Atlas that lists the overpass heights.  Since we don't travel much and spend longer periods of time in one place, I've not seen a need for an expensive GPS.

Terry

We don't rely on GPS information for low clearances. My common quote is "They only have to be wrong once" and we don't trust that the GPS databases are 100% accurate.

Instead, when planning a route where I think this may be an issue, I refer to the America's Independent Trucker's Association (AITA) website aitaonline.com. Under the "Information" tab, you can click on each state and then click on Low Clearance/Bridge Height information. Though they have a disclaimer that they can't guarantee accuracy, I feel much more confident in the information being provided to and being supplied by truckers that have important commercial interests in this data.

Coach-Net has an easier-to-use PDF file - Low Clearance & Bridge Information - that appears to mirror the AITA data. The Truckers Atlas (or more specifically "Motor Carriers' Road Atlas) as Terry mentioned, is also a good source. Still, I prefer to use the online database because it is more likely to be updated more quickly if there are changes.

State statutory standards require heights to be 13'6" to 14', but many overpasses that are lower have been grandfathered or exempted. The federal requirement on interstate overpasses is now 16', but again, some older overpasses are not that high and have been exempted.

Of course, we plan our routes before we travel and check this information before getting on the road. However, sometimes there are detours we were unaware of, and then we just pay very, very close attention to clearance signs.

This probably goes without saying, but it's extremely important to know your exact height. We measure from the ground to the top of our highest accessory on the roof (vent cover, air conditioner, or whatever it may be) and then add a few inches for safety margin. I then have that number taped to my dashboard for quick reference when we come upon a low clearance sign.

This is just the way we do it, and in over twelve years of living and traveling in our RV, we haven't hit an overpass nor have we had to turn around to avoid a low clearance.

I use a Garmin Dezel 770 (which is a trucker GPS) ... I believe they also sell an RV 770 ... which is basically the same unit. It allows you to set your weights and length and height and will route you either like the big vehicle you program or like a car. You can also chose to avoid tunnels, toll roads hazardous cargo restrictions (LP tanks), etc. pretty good unit. I also subscribe to a Low Clearances website which downloads a database of bridge clearances that is an "add on" to the GPS's data. With this, I can set my personal clearance alarms. I'm 13' tall, my personal comfort level is nothing lower than 13'6". I have my GPS set to alert on anything 14'6" or less.