I'm generally anti-facilities, but I have to admit that the Arlington-area bike trails are quite useful. On the way to pick up our cars from the shop over in Falls Church, I can ride nonstop for five miles -- an amazing experience. They return sone of the cycle access that was destroyed when limited access roads (like I066) replaced local roads. They are generally quite OK during rush hour commuting, but turn into madhouses on weekends.
Paul