The plug-in trials in Seattle have shown a big improvement in fuel economy, going from 51 mpg to 57 mpg in June (Plug-In Hybrids’ Fuel Economy Lookin’ Up In Seattle | Autopia | Wired.com). That's a big improvement, and although still below expectations, it's a factor of two things.
First, the weather improved. Just as with conventional gas engines, the warmer weather helps improve fuel economy. The second big factor is education.
Driver behavior plays a huge role in maximizing fuel economy in a plug-in hybrid. You’ve got to use a light touch on the accelerator, mind your speed and plug in at every opportunity to keep the battery charged. The plug-ins are divvied up among the city, King County, Seattle City Light, the Port of Seattle and Puget Sound Air Quality (a 14th car in Tacoma wasn’t included in the current data set). Fleet managers have been telling drivers how their driving style impacts fuel economy.And it's one that car makers have got to keep in mind. The success of plug-in vehicles is going to depend on educational efforts by auto makers as they sell the vehicles. If a customer comes in, expecting 100+ mpg, but only get 50 mpg, who's he going to blame for it? What do you think his outlook is going to be like? What do you think the media is going to say about it?
“You hope the message is getting through. It’s an educational effort,” Thomsen said.
At the prices expected (estimates for the Chevy Volt put it at $40K), customers are going to expect a little magic. Not 51 mpg. Especially since current hybrids that you don't have to plug in can get similar numbers (the current Prius has an EPA rating at 50 mpg).
The plug-in hybrids being used in the Seattle trials are converted 2005 Prius, which were rated at 46 mpg by the EPA.
It’s worth noting that the Prius wasn’t designed to be a plug-in hybrid. The biggest problem is the electric motor is too small, so the car relies more heavily on the gasoline engine. Software also limits the top speed in all-electric mode to 34 mpg. Anything more than that and the engine takes over. Cars designed from the ground up to be plug-in hybrids, like the plug-in Prius that Toyota is working on will almost certainly offer far better fuel efficiency than a converted car.