Motorway Mayhem caches are close to motorway junctions, so you can break up a long journey with a quick cache-and-dash. Estimated time from M4/cache/M4 is around 10 minutes
Nothing to see here - just an off motorway lay-by about 1/2 mile from junction 5, and a 75 yard walk.
Cache is a very small micro. Bring tweezers.
Good luck, and if you decide to do a U turn - be very careful!