The cache is not accessible from the M40, only from the local road passing above it.
A simple cache and dash for those passing by. You should be able to find parking close by.
As I use the M40 every working day I thought I'd add a few caches along the route of this busy motorway to show what you don't see from the carriageway at 70mph. Not always a spectacular view but I hope of some interest anyway.
Please take care when parking not to cause an obstruction and keep watch if you need to cross the road.
You are looking for a small clip-lock box.