and there is also a program called polygon cruncher that you can find over the internet.. it will decrease your polygons number but it will mess up your mesh (it will be harder for you to apply your skin so be careful)... you may want to try it, especially if you're very good at skinning (UVW wrapping).
Also, try to remove unueful polygons (the ones you'll never see in-game) that means, the one under the tracks, and between them. Ex:
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TOP VIEW
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the polygons in red are useless
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Doing that, you will decrease your polygon count by 50%!