The team used the "pulse and glide" technique, which seeks to minimize energy conversion whenever possible. Energy conversion occurs when fuel is converted to kinetic energy (motion), when kinetic energy is stored (charging the battery) and when stored energy is converted back into kinetic energy (discharging the battery). Each conversion results in losses that consume more fuel.

What's in it for us?
Not only is this record-setting run exciting news, but there are practical benefits for the rest of us. Some of the principles of the pulse and glide method used in this run can be adapted to everyday city driving to increase fuel economy. See the article on improving your mileage in this issue of Hybrid Synergy View for more details.

Who are these guys?
After sharing information in online hybrid mileage forums, these "hypermilers" decided to try for record mileage at a weekend marathon last August.

Dave Bassage, Director of Innovation, West Virginia Department of Environmental Protection, said: "An unexpected effect of hybrid driving was a total change in my driving style, from a former speed demon to an mpg fanatic, eternally driving for 'high score' on the trip mpg readout. My vanity plate reads NVIROCAR."

Dave says of team member Dan Kroushl, Pennsylvania, "He's incredibly devoted to nursing the maximum possible out of his Prius, found the course and developed 'pulse and glide' to an art form."

Wayne Gerdes, nuclear plant operator, Illinois, uses the screen name "xcel." "I try to 'xcel' at hypermiling anything I can get my hands on."

Rick Reece, geospatial analyst, South Carolina, owns the most hybrids on the team: two 2004 Prius with option package nine, a 2001 Prius, and another hybrid. Rick really likes to use his Bluetooth® hands-off phone in the Prius.

Bob Barlow, self-employed attorney, Virginia, said: "I hypermile because I want to get the most out of my hybrid and I challenge myself to find the car's limits."

Pulse and glide unplugged
Dan Kroushl writes:

"The pulse and glide technique seeks to minimize the amount of time that the engine runs, and minimizes power flowing to and from the battery. The pulse refers to deadband acceleration (no flow to or from the battery) up to 40 mph. Next comes the glide (engine is stopped, no flow at all) where the speed slowly decreases to 33 mph. The cycle continues until a stop is required. At such time the brakes are applied and some regenerative braking helps to maintain the battery level. Brakes are also applied if a downhill stretch causes the speed to exceed 40 mph.

"The order of preference is: glide, coast, regenerative brake, conventional brake. The goal is to minimize the time you need to engage the brake pads, and do as much as you can with the most optimal method for slowing.

"On level roads, the rate of acceleration will be about equal to the rate of deceleration. That suggests that the engine would run approximately 50% of the time. So the fuel economy would be twice as much as indicated during acceleration. I have recorded mpgs in the low 90s on level roads.

"Contrary to popular belief, a route with gently rolling hills can increase mileage. This is because the pulse happens when climbing the hill and the glide happens during the descent. The fuel economy will be lower while climbing but the glide will last much longer. On some routes, during pulse and glide the engine need only run about 25% of the time, yielding four times better fuel economy than indicated while climbing the hill. I have recorded more than 100 mpg (estimated at over 104 for over 100 miles) on a route with gently rolling hills.

"In some situations, the pulse technique might require modification if there is not enough regenerative braking (stoplights, braking to maintain 40 mph downhill) to maintain the battery level. Even though pulse and glide does not use the battery to propel the car, battery power is required to start the engine at the beginning of each pulse. Likewise, battery power is required to power the electrical systems (estimated at 600W continuous). If you notice the battery level dropping to four bars, change the pulse technique from deadband acceleration to charging acceleration. This is a slightly slower rate of acceleration where the engine also charges the battery. The fuel economy during acceleration is about the same but the engine runs longer, so economy will decrease until your battery level recovers to five bars. If your battery gets below four bars, it is nearly impossible to glide, as the engine will want to charge the battery."