Navigation How To?

Can anyone help with this problem:

I drove from Devon to Yorkshire a few days ago, starting from Awliscombe, in an area I don't know at all, so I trusted the sat. nav. at the outset. It offered me three routes or varying apparent stupidity, and I took the first, which was shortest. I thus joined the M5 at Taunton, after 23 miles of solid traffic, and then M5/M42/M1 as normal. However, it attempted to take me off the M1 at every junction as far north as Doncaster when clearly staying on the M1 was far better. On looking back, I see that Awliscombe is on a road which leads directly to the M5 (in the opposite direction to which the sat. nav. took me), a distance of only 8 miles.

It appear to pick the literally shortest route , if only by a fraction of a mile, rather than the quickest (i.e. motorway) route, seemingly for 'green' reasons (all routes come with green leaves indicating which option is 'greenest'). Is there any way to force it to pick the quickest route, rather than shortest?

It also tries to avoid any slow down if you have selcted it to avoid all resulting in similar behavior.
I have mine set to avoiding just the larger ones and that has made it a bit more usable.