An expert in what? Well, anything. Let’s make some very broad generalisations: your commute will afford you 30 minutes of uninterrupted time, twice a day, five days a week.
Assuming you have six weeks’ holiday a year and work for 45 years without hiatus, that is 10,350 hours to do with as you please – within the confines of your mode of transport, of course.
Malcolm Gladwell’s famed 10,000-hour rule (that this amount of deliberate practice is the common trait of world-class practitioners in a given field) should jump immediately to mind.
The number is obviously arbitrary and has been debunked more than once, but the important thing should be the possibilities it suggests, should you decide to devote the time to something worthwhile.
Let’s just hope your expertise extends beyond memorising the junctions of the M1 or your local train timetable.