Jeff --

I looked into coverting my Specialized Crossroads about four years ago. The main problem is that derailleur bikes have vertical dropouts, rather than the horizontal ones required for internal gears, singlespeed, and fixed. The solutions are to braze in a new set of dropouts (expensive) or add a chain tensioning device called a singulator (which, like a derailleur, may not be happy in ice and salt). I concluded that buying a new bike was the more economical solution. Buying a singlespeed frame and moving your components over is another possibility.

Paul