…and regrettably there's no easy way of avoiding Watford. It's a bit of a nightmare ring road to get through and out the other side from the Bushey direction. Mind you, on a Sunday morning, it shouldn't have the usual snarl-ups and jams.
I believe it's legally possible on a bike to carry on in a straight line once you get past Watford High Street train station and up the High Street and under the subway at the very top end, avoiding the ring road, though I'm not 100% certain on the legality or otherwise. @
jayonabike may be better informed.