routes.rb bad performance

My config/routes.rb is about 200 lines.

I do some experiment with two different routes.rb, a) routes.rb with 200 lines, and b) routes.rb with only one line ( map.connect ':controller/:action/:id')

and the result,

a) takes 0.4s, and b) takes 1.7s

My routes.rb is not very complicated, just some string matching like map.connect 'user/:username/home/:action/:id' , :controller => 'user_home' ... but I really need those routes setting.

Any idea how to improve the performance?