Toyota summarized the results of a 200-unit plug-in Prius trial in Europe that showed that the 23 km electric-only range of the plug-in Prius was adequate for about 65% of trips, and that user behavior was the critical factor in overall fuel economy.
In the trial, 43% plugged in their cars fewer than 3.5 times a week, 25% of users plugged in their cars between 3.5 and 7 times a week, and 32% plugged in their cars more than 7 times a week, for an overall average of 0.9 times per day. In comparison, users in Japan's Toyota City plug in their cars an average of 2.1 times per day. So while Japanese drivers use an average 2.23 liters of gasoline per 100 km (103 mpg), the European drivers used an average of 4.33 liters per 100 km (54 mpg). To put those figures into perspective, Toyota advertises an average fuel consumption of 3.9 liters per 100 km (60 mpg) for the newest plug-free Prius. I guess there's some merit to the theory that it works better if you plug it in. So we do need lots more public recharging stations after all - in this case to keep the plug-in hybrids running on electric not petrol.
