Why does 18 wheels of steel extreme trucker run so slow

It must be your computer and just can't handle it. I too had the same problem, but then I downloaded swift shader and put it in my 18 WOS Extreme Trucker files and loaded the game up, boom! It is running rather smoothly.......A lag spike here in there but much improved from before. I am also running on a laptop, windows 7, with no other programs running.....Much more playable now!