Freeways ? The Hybrid Synergy Drive system, a continuously variable transmission based on planetary gears does not allow to exceed 99 km/h in electric mode, making it difficult to merge into traffic. This maximum speed is also difficult to reach as total electric power is limited any excess pressure on the throttle pedal will spark the gasoline engine. Even if you adopt a slow cruise speed (80 km/h), a long incline can be enough to trigger the 4 cylinder thermal unit. It is difficult to isolate all the factors that can result in a switch from the electric ‘EV’ mode to the hybrid ‘HV’ mode, but these include use of the heating system and other mechanical necessities, translating into a vague message ‘EV mode unavailable – warming up”. A consequence of not-so-extreme winter temperatures ? Difficult to say, but the fact is that imposing EV mode until batteries are empty is not always possible.

The subjective appeal of a rechargeable car is the ability to enjoy electrical drive over extended journeys, without the noise and vibration inherent to an internal combustion engine. The Prius III Plug-In can deliver against this expectation, but in conditions limited not only by its moderate range, but also by other unpredictable factors. I would be inclined to speculate that Toyota has adopted a very conservative approach to the management of the Lithium Ion battery, and that a sustained solicitation triggers a handover to the 1.8 liter VVTi  engine.

Another telltale sign of this conservative approach is the limited torque available on tap. In comparison, the Nissan Leaf and Opel Ampera are much zippier and feel measurably faster off the line than a decidedly very calm Prius. Even if the exercise is in thorough contradiction with the very “raison d’être” of these cars, one of the enjoyable aspects of electric cars is the ample availability of torque and the fun of fast acceleration in near total silence. Nothing such here, petrol is required for swift reactions, electric propulsion is reserved for energy-efficient mobility.

I trust Toyota engineers and the unique experience they have from millions of cars covering hundreds of billions of miles with unquestionable reliability, but the prospective buyer must make his (or her) mind in full knowledge: the Prius Plug-In only offers a fraction of the pleasure to drive an electric car and is rather to be considered as a hybrid on steroids. With this car, electric drive is an opportunity, but cannot be an obsession.

From this angle, the Plug-In Prius displays good fuel economy. We measured 4.72 L/100km (4.4 L/100km at an average speed of 70 km/h according to the on board computer), with an additional 33.6 kWh of electricity drawn from the power grid, the equivalent of 11 charge cycles. There are several ways to analyze these figures.  The eleven charge cycles allowed us to cover around 200km in electric mode at a cost of 33.6 [kWh] * 0.145 [CHF/kWh] = 4.88 CHF, or the economic equivalent, at today’s pump prices, of 1.35 L/100km. The remainder of our 1848 km road test required 87.23L of 95 unleaded, translating into an effective mileage of 5.3 L/100km in hybrid mode. This value is consistent with the 5.44 L/100km measured with a Prius II over 50’000km, and lower than the 5.7 L/100km we computed in our Prius III road test under more severe conditions (passengers, higher cruise speeds, alpine roads in the mix).