PA24 pilot reported fuel mismanagement resulted in an off airport landing.

Narrative

I was flying for the purposes of a taking a family member on sightseeing flight. The condition was Marginal VFR with Ceilings around 1800 AGL / Visibility was reported at 10 miles. The air was about 45 degrees and the humidity was very high but not sure exactly how high. In these conditions I felt like Carb Icing would be the biggest potential of any problems. After flying for about 45 minutes; I felt a sputter of some sort which alerted me to a possible carb icing problem; so I immediately pulled the carb heat for a minute. The sputter stopped just as soon as it started so I assumed the Carb Heat did fix the issue. About 4 minutes later I felt a sputter again and again pulled the Carb Heat - but the sputter didn't stop this time. It was at this time that I started to proceed with finding the best place to land in case I wasn't able to re-establish power. The Prop was turning; and engine was running but not enough to maintain altitude. I was about 1300 ft AGL and the plane started to descend at a rate of about 600 ft per minute. I immediately found two suitable places to aim for one was a field next to a county road and was the county road. With the little time I had to work with I was able to switch tanks and check for other issues; but it wasn't enough time to squawk 7700 or make a radio call. There were 3 cars on the road below; but I was going to be landing about 3000 feet in front of a car that was with the flow of traffic and about a mile before I was going to meet any oncoming traffic. After landing - one of the good Samaritans stopped and called the local authorities. After a few minutes some law enforcement cars pulled up. They assisted in helping push the plane to the grass. Over the course of the next hour; I was on the phone with a few different people. I was able to determine that the issue was most likely caused by the empty right fuel tank. The MSG on the Garmin 530 alerts me every hour to change tanks. I missed the MSG on the Garmin 530 to do just that. The empty tank could have [caused] the issues that made the engine sputter and disguise itself to me as Carb Icing. It was after about 20-30 minutes after I landed on the road that tank in the right was completely empty. I did try to start the plane on the left tank. After determining that the issue was an empty fuel tank on the right and having 20 gallons on the left the officer said he would block off the road if I felt like the conditions were safe to take off. My wife arrived before I took back off and I flew the plane back to my home airport about 20 minutes away with only myself on board the plane. Corrective actions for the future will be to delete the MSG on the Garmin 530 and utilize and become familiar with the Fuel Scan 450 that is currently installed on the plane. Other Actions will also include re-evaluating personal minimums with a CFI. Other Actions will also be to always depart with full tanks whenever it is permissible to do so with consideration of Max Gross Weight.