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

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 =>

but I really need those routes setting.

Any idea how to improve the performance?