I don't know how fast the train would be going at this point but let make some assumptions.
Assume 30 mph = 1/2 mile/min = 44 ft/sec so with your 1/160 shutter speed the train will move ~3 inch while the shutter is open hence the blur of the train. (60 mph = 6" moved etc) Notice further back down the train, the blur appears less because the angle that 3" creates is smaller because of the greater length of the sides of the triangle so the apparent movement is less.
So why do the wheels look sharper? Well the rims of the wheels are in contact with the track and as the train is moving along the track at 30 mph (our assumption) the rim of the wheels is also move at 30 mph. If the wheels are say 4' in diameter, at 2' from the centre the spokes are only going to have moved 1.5" ... the nearer the centre you get, the less movement. So that coupled with the fact that they are some way back from the front of the loco, makes them look sharper than the front
The only way to get the effect you are after is panning. Making another assumption, say its a 24 spoke wheel, I would suggest that to get the sort of blur you are after you might want the wheel to turn say 2 spokes worth while the shutter is open. So 4' wheel has a rim diameter of ~12' (diameter x Pi = D x 3.14) so the spokes are 6" apart at the rim so to move 2 spokes worth ie 12" would suggest a shutter speed of ~1/40 sec or more.
Look at
this image in Foxy's gallery taken at 1/160 ... & I bet that prop was spinning much faster than your train wheels
