So I got one for about $200, cheap but not the cheapest.
When I try to get it to calculate long trips, it always takes some crazy detours, like exiting the freeway to travel on some two lane road for six miles to then rejoin the freeway.
I remember this was a problem with mapquest in its earlier days. Is there a setting I can change, or should I pony up more $$$ if I want accurate driving directions?
Why don’t say what kind you have in case someone with experience with that particular model can reply? We have the Magellan cheepie that fits in that price range. It does take some wacky roads, but theres a nifty option to say “avoid this road”. That usually works for me, along with a dose of common sense to know to stick to a road until it auto recalculates based on the road I’ve chosen.
So, I guess what I’m saying is I had to get to used to the GPS instead of making it work 100% like I expected it too. We’re friends once again.
Okay, It’s a Garmin c330…I’ve got the crazy little fucker beside me driving the route I will take next weekend. Some crazy directions it has, but not as bad as my wife, and she cost me more than $200… 
I work in this industry as a software engineer (though I won’t reveal the specific company).
It is extremely difficult to create a real-world routing system that is both fast and gives good results in all circumstances. Especially for long distance routes. There is always a big tradeoff between exploring too many roads (thus taking too long to calculate a route) and exploring too few roads (thus missing the one road needed for the best route). Both the map data and the algorithm have to be tuned to get the best result, and there is no tuning that will work for all possible routes.
But people in this industry have spent many man-years on this problem, and some companies have better systems than others.
If I had to guess, in this case the algorithm made the calculation that the smaller road was sufficiently shorter than the freeway that the overall time would be less if the detour were taken. But that’s without seeing the actual situation.
Ed
I don’t have that particular model, but in mine, there is a setting where you can change the route to either “fastest” or “shortest”. You have yours set to shortest.
eta
Of course, you could always read the manual (page 21) 