CHRIS ALLEN, 25, an RTP programmer, commutes from Cary.

"I use a stopwatch to time all of my work commutes, just to make the drive a little more interesting. ... For a while, I took several different routes to and from work and timed them all separately so I could figure out which was fastest. ... I did find that the I-40 routes were the fastest. The fastest routes that didn't incorporate I-40 involved taking NC-55 and US-64 via Apex [and] were between 5 to 10 minutes longer. That way may have been about a mile shorter than I-40. (Fuel use is probably about the same -- NC-55/US-64 is shorter and lower speed, but with more traffic lights.) I also tried several more direct routes through downtown Cary, but those were quite slow."

SAVING RECEIPTS

BILL OWENS, 53, an Embarq business analyst, lives in Wake County.

"Before this travel diary experience, I was already keeping track of all gasoline used in all vehicles in my family, calculating mpg and keeping up with price per gallon and total cost," Owens said.

Method he uses: Each time Owens visits a gas station, he resets his trip odometer. But first, he jots down the trip odometer reading on his gas receipt. It should be the number of miles traveled since the last fill-up. At home, Owen enters numbers from his receipts into a spreadsheet to calculate his miles per gallon.

He compares this with the mpg his car's system calculates. In his Nissan Altima, the estimated mpg is a usually off by one or two miles per gallon. In his wife's Buick Rendezvous, the estimates are usually on target.

ONLINE SITES FOR HYBRID OWNERS

ALAN FALK, 62, is a Prius driver who lives in Raleigh.

Before he got involved in the "Gas Chronicles" series, Falk was already keeping his own color-coded spreadsheet, with mpg averages for his drives across the country and North Carolina. Falk also has been uploading his mpg stats onto www.greenhybrid.com, a site where hybrid owners share practical advice and compare their fuel efficiency.

"You can see the data for hundreds of people who are a little obsessive-compulsive and religious about their hybrids," Falk said.

LOW-EMISSION SUV IS A GAS GUZZLER

SUZANNE LUCEY, 40, of Wake Forest spent $125 in her diary week on gas for her 2007 Honda Pilot.

"I really had no idea I drove that much. ... I underestimated what I spent on gas by about $60, and my low-emission vehicle is actually a gas guzzler. I am getting a bike."

DO MORE CAR MAINTENANCE

REBECCA PADEN, 27, of Raleigh is a state government analyst.

Her 2000 Toyota Echo's "check engine" light had been on for years, Paden said. She had ignored the warning while the car was registered in Hoke County, a county that doesn't test for emissions.

When Paden had her car inspected during diary week, it failed the emissions test. So she let a repair shop replace the air filter and spark plugs and clean the oxygen system -- changes the mechanic said could improve her gas mileage.

"Keeping a travel diary helped me realize just how much traveling I actually do. ... One thing I'll change as a result of this exercise is to take better care of my car, and give it the love and attention it deserves."

KEEP TIRES INFLATED

KEVIN LITTLEJOHN, 23, commutes from Chapel Hill to Raleigh in a 1995 Volvo station wagon.

Day 1: Filled up at the Shell gas station at Blue Ridge and Beryl roads. The gas mileage was 19.64. "I realize that my gas mileage is lower than usual; it is usually 20 to 21 mpg."

Day 6: Filled up at the same Shell gas station. Gas mileage: 18.99. "I went to the gas station after work and filled my tires with air. ... I put an extra 10 psi [pounds per square inch] in each!"

A week later: "My gas mileage is better after I pumped air into my tires ... about 21 mpg now, which is better than before, and it'll make a difference in the long term."

What I learned keeping a travel diary

To calculate your MPG, follow these easy steps.

STEP 1. Completely fill your vehicle's gas tank, and jot down your odometer reading (mileage).

STEP 2. When it's time to refuel, fill the tank completely. Write down the number of gallons it took to fill the tank and the vehicle's new odometer reading. Once two odometer readings are taken, MPG can be calculated.

STEP 3. Calculate the distance driven by subtracting the previous odometer reading from the new one.

STEP 4. Divide the number of miles driven by the number of gallons it took to fill the tank. The result is the vehicle's MPG for that driving period.

OTHER RESOURCES

AAA's www.fuelcostcalculator.com has links to current prices and a calculator that estimates how much you'll pay to fuel your car for a trip you're planning.

The federal government's www.fueleconomy.gov offers gas-saving tips, fuel-economy ratings of cars and trucks, and information on hybrid cars.

Other Web sites can help you find the lowest prices on gas. Try www.GasBuddy.com, www.gaspricewatch.com or aaacarolinas.com.