Toyota Prius: Taking the lead foot out of driving

The advent of hybrid-drive vehicles has placed in question the eternal verities of fuel economy. Open roads are now to be shunned, for example, and shifting to neutral provides no advantage whatsoever in a car with a CVT.

Most of the principles continue to apply however, but from our own experience, open-road driving is not the sort of driving environment in which cars like Toyota's latest Prius can excel.

While the Prius is no fuel hog on freeways, it definitely delivers its best in the city and suburbs.

But conventional fuel-saving techniques aren't necessarily going to yield the same results they might in a conventional car.

Toyota, during the media launch for the Prius, ran a 'competition' to show journalists how to balance CO2 emissions (and fuel economy by association) against setting a competitive time around a 'race track' at Camden Airport, south-west of Sydney.

The company prepared a Prius with its tailpipe emissions monitored electronically and allowed the journos to 'compete' (pictured) -- to see who could get the fastest optimum time for the lowest CO2 emissions.

We're ashamed to admit that -- as second driver out on the track and without the luxury of attending the briefing beforehand -- the Carsales Network entry didn't fare well. Neither fast enough nor gentle enough on the right pedal to feature in the top half of the field. Still, at least our entry wasn't disqualified for finishing too slowly.

That was the major stipulation: If you drove so slowly that the car could circulate under electric power alone -- thereby generating zero CO2 emissions -- your time would be more than 20 per cent outside the benchmark time set by racing driver and broadcast commentator Neil Crompton. A couple of journos fell victim to this, with one recording a CO2 output of just 29.9g/km -- but circulating the track in a 'geological aeon' time of 108.4 seconds.

By comparison, this writer was a profligate polluter, at 83.9g/km, but got around the track in a still slow 92.2 seconds. The winner of the event was slower still, at 96 seconds, but emitting just 43.8g/km of CO2. As each driver participated, it became clearer how one could 'cheat' to extract the best outcome. It's no surprise that the winner was also the last person to drive the track -- and by then he'd gathered all the intelligence to work out the best driving style.

All good fun and interesting, but how much of it is practicable in real life? Not that much, in actual fact. In the event at Camden Airport, you were penalised for perfectly legitimate tactics you can use quite safely in real-world traffic (like using the EV mode in the Prius for a relatively fast get-away without impeding traffic or running up the petrol engine).

On the other hand, maintaining high speeds and wide lines through corners, with minimal braking prior -- a tactic encouraged at Camden -- is plainly impractical on the road. And there was no traffic behind the competing car at Camden to honk horns at the hybrid.

As it is, the Prius offers a number of innovations that aid the driver to extract the optimum fuel efficiency from the car. Based on our time with the Prius subsequent to the CO2 race at Camden, we would recommend the EV mode be used as much as possible.

As already mentioned ad nauseum in our Prius blog (more here), the EV mode relies on power stored in the car's Nickel-metal Hydride battery pack to run the electric motor driving the front wheels. This is as near as you'll ever get to something-for-nothing.

Say you're at the base of a hill; the EV mode will provide sufficient power and torque to accelerate the Prius up to speed before the petrol engine takes over for the remainder of the climb. By the time the petrol engine cuts in, the car is already up to a speed at which the continuously variable transmission (CVT) is operating in a higher ratio, so the petrol engine is operating more efficiently, using less fuel for a faster road speed than if it had to take care of moving the car away from a standing start.

You might be thinking at this point that the power drained from the batteries still has to be recovered by some means. That's true, but it's axiomatic that every uphill climb is complemented by a descent -- and it's on the downhill run that the Prius can recover energy (kinetic energy) and convert it to electrical energy to recharge the batteries. That's where your 'something-for-nothing' energy gain comes in.

And here's where you as the driver can help that. The Prius offers a 'B' mode in its CVT. This mode provides more aggressive regenerative braking. That means that if you are on a downhill run, you can pull the gear lever straight back into 'B' mode and recover more power than would be the case if the lever was left in 'D'. Think of it more as engine braking in a manual transmission car -- but with further benefits.

In the Prius's multi-information display, there's a screen to show you how much energy you're using. In the left of the driving style screen, there's a small box marked 'chrg' ('charge') which illuminates from right to left according to how much the batteries are being recharged as you coast or brake. Most drivers brake harder than they accelerate, which means that in theory, braking will recover energy quite rapidly.

Unfortunately, the regenerative braking can produce more power than the batteries can handle, so during harder braking, energy that could be recovered is lost. You know when this has happened when the charge box is fully lit. The trick with braking is to find a rate of deceleration that will illuminate nearly all the charge box, but without putting yourself and other road users at risk. That includes paying attention to the traffic ahead...

While the hybrid vehicle is not placed at an advantage on freeways, it can be quite frugal during peak hour, when traffic density might limit speeds to 80km/h on the flat. This being the case, the hybrid's petrol engine will be operating, but in a relatively light-load situation. Based on the Prius, you could expect to average under 4.5L/100km if you only ever drove the car on freeways during peak hour and the speed never exceeded 100km/h.

If fuel economy is ultimately more important to you than your ETA, tag trucks. They don't accelerate so fast that the petrol engine in the Prius needs to provide supplemental motive power, and they also brake slower than cars. At higher speeds they reduce aerodynamic drag for the car following -- at a safe braking distance as well.

Here's another couple of tips for improving your fuel economy driving the Prius. Avoid driving at night, if you can help it, and try to keep the car parked under cover during summer days, because while it has solar-powered cooling for the interior when left out in the sun, this system will still struggle to keep the temperature down in Australia's harsh climatic extremes. The more you use air conditioning, the more fuel required to run the engine and keep batteries charged.