The opinion expressed here is my own. The information is less about actual fact and more a personal perception gained through one short term experience.
The decision to undertake driving in the UK as a tourist from another country is not to be taken lightly. The risks are high, and the opportunities for failure are innumerable. The idea that one can present an Oregon driver's license at the rental agency and they will give you a car and keys with no questions asked borders on the ludicrous. The responsibility of understanding the rules of the road lies entirely with the driver and there is no questioning of the depth or breadth of your experience.
The differences in signage and basic driving rules are significant enough without adding the complication of sitting on the wrong side of the car, on the wrong side of the road, with the gearshift in your left hand. If these things are not disorienting enough on their own, add in the fact that in 1,000 miles of driving we didn't see a single stop sign, only a handful of signals, and iterally hundreds of clockwise roundabouts. I don't know that there is an orientation program available that could adequately prepare one for this experience.
I consider myself an experienced driver. I've been driving for nearly 50 years. I have logged at least a half a million miles behind the wheel. I take driving seriously - I don't talk on the phone, text or participate in other distractions while driving. For the most part this experience means very little, and in fact can result in spectacular failure when presented with a situation that requires an instinctive reaction from the driver. Driving must be approached carefully and thoughtfully every step of the way.
My success, and I do consider the experience a success in spite of the fear factor, was due to a few very deliberate preparations. First - visualization. I spent hours visualizing driving on the 'wrong side' of the road. True, many of these hours were between 3 and 4am as I lay in sleepless anxiety of the impending experience. Second, I read about differences in signage and did my best to understand what would be expected of me as a driver. Third, I ensured I had a full-featured GPS application with live data connection. I selected a Garmin app for my iPhone that offered detailed information on the hundreds of roundabouts we would encounter in our travels. And, finally, a competent navigator. Simply listening to the instructions from the GPS without additional contextual information provided by a live, analytical observer would have been insufficient. Our success was a team experience.
A word about roundabouts. In light to medium traffic they are amazing tools to keep traffic flowing without the stop and start of 4-way stops and signals. In heavier traffic they are a nightmare of the worst order. Our drive from Eastbourne to Penzance, a distance of about 320 miles, included 87 roundabouts. These roundabouts aren't the orderly conjunction of two, two lane roads around a small center circle like we see around here. These are frequently the confluence of three or more roads, frequently a mix of 2 and four lanes, converging on a racetrack-like pad covering one to five acres with five or more exits from which to choose. They are initially terrifying, frightening with a little experience, and like watching ballet from the safety of the sidewalk.
And, finally, trip planning. In the western US, 300 miles is an afternoon drive, arriving in time for dinner and a show. 600 miles is a reasonable day, and a thousand miles can be covered between dawn and dusk on a long summer day. Don't expect to make similar times when driving in the UK. Leaving time to negotiate a hundred roundabouts and recover from missed turns, we found 300 miles to be a challenging day's drive. With the realities of UK driving this is not relaxing siteseeing. It requires intense concentration to keep from spoiling the day by smacking headlong into something or someone you never saw coming.
All in all, I've never been so pleased to return a rental car with all of its fenders still attached.