During a week of keeping travel diaries for The News & Observer, some volunteers learned their cars were getting better or worse mileage than they had thought. Others took vows to cut back on unessential travel. Almost all said the diaries gave them a better handle on what is dictating their fuel consumption.

"I learned ... if I want to put fewer miles on my car, the best thing I could do is move closer to work," said Chris Allen, 25, a programmer in Research Triangle Park and frequent road tripper.

Many of our diary keepers had not kept travel logs before but patiently endured the tedious moments of jotting down date, time, place and odometer readings whenever they cranked up or cut off their engine.

Nan Holton, 49, a caterer from Wake Forest featured Monday, said she enjoyed participating in the series but was thankful she did not have to keep a travel diary for more than a week.

"There were times I felt like 'cheating,' " she said, "like when I went to Chick-fil-A, I thought, 'She will never know I was here, I will just merge it in with the trip to the dentist.' But guilt crept in, so I recorded it!"

Keeping a log did highlight, however, how many miles she travels every day, Holton said. Before, she often could not figure out how she had put so many miles on her car.

Travel diaries are a tool transportation planners also occasionally use to gain insights for long-term planning. In 2006, researchers at N.C. State University collected trip logs from about 5,100 households in a 12-county area surrounding the Triangle. The data are being used to create models of the region's population and travel patterns, said Joseph Huegy of NCSU's Institute for Transportation Research and Education.