Whilst travelling by motorised transport, vibrations felt may cause male passengers to develop an erection.
"....The car journey was taking forever but luckily Alex had developed somewhat of a Travellers Marrow to entertain him ...."

"....The rest of the coach passengers gasped in awe at the Travellers Marrow, the sleeping Alex was sporting...."
by KingKempo February 10, 2010
Get the Travellers Marrow mug.
An unexplained semi or erection while driving long distance, usually alone and stuck in a traffic jam. Know to mainly affect Sales reps.
Sorry I'm late for my appointment, I was delayed by an unexpected Travel marrow.
by giblet10 November 19, 2010
Get the Travel Marrow mug.