Many years ago, before the underpass was built, this junction
was a plain and simple roundabout. At that time, the M8 and M9 both
started at this roundabout, the M8 heading west towards Glasgow,
and the M9 north-west to Stirling. Even after the underpass was
built, the M8 and M9 still both started at this point, even though
there was no discernible “junction” between the motorways.
Recently however, the M8 from Glasgow was extended to end
(actually begin, but lets not quibble about that) at the City of
Edinburgh Bypass, which meant that the M9 now begins a mile or so
up the road at its junction with the newly extended M8 instead of
here at Newbridge as it used to do.
You can access the cache by either the B7030 or A89 from the
Motorway. HOWEVER, if your vehicle is more than 2.0m wide, you
should use the A89 due to a width restriction on the B7030.
The cache area is actually an ancient burial ground. The tumulus
was originally surrounded by a number of standing stones. Today
only 3 of the stones remain. See here
for more details.