In message , at 19:32:37 on Thu, 3 Nov
2005, Dave Arquati remarked:
Leaving Harrow in the morning, returning evening.

You will be going against the prevailing traffic, so it shouldn't be a
problem once you get to the A40.

...although sometimes Handy Cross (M40 junction 4) and the A404 can be
a bit of a pain.

I've often been held up in a two lane jam all the way up the hill to the
M40 from the Marlow junction. The OP should consider other ways to get
from Marlow to the M40, if possible! It might even be quicker to go down
to the M4 and east as far as J3, then north through Yeading and
Northolt.
--
Roland Perry