Version 2.03, July 27, 2006 - Added high-speed, NHW20 Prius data

Introduction

After having to replace our Camry, we bought a 2003 Prius on Ebay and drove it back to Huntsville. Since then, we've been working to maximize our return on investment.
Associated Project Pages

Fuel Efficiency Index:

Miles Per Gallon Performance

We have the following data based upon pump measured consumption and trip meter recorded distance:

The following chart compares theory to benchmark measured results:

Prius Efficient Route

Measuring the city performance requires investigating two routes: The Prius has significantly better city performance than highway numbers. So to maximize MPG, we try to use city driving as much as possible. Fortunately, this allows use of short-cuts that eliminate longer highway speed miles. The short-cut distances mitigate the slower speeds with a minimum reduction in trip time.

The Prius route attempts to emulate the EPA city profile and minimize interactions with traffic that seeks higher speeds. Highway speed sections are driven at 51 MPH in the right lane going between nearly adjacent exits. Accelleration to 51 MPH happens on descending ramps and down-slopes. Decelleration occurs on up-slope exits to maximize regeneration and when safe, up-slopes are climbed at the minimum safe speed.

During the warm-up phase, manual stop is used until auto-stop begins working. Also, neutral coasting is used on level and up slopes while the ICE continues to run at idle.

The rear-view mirror is used to make lane changes to avoid tailgaters. Turn signals and the emergency flashers are used as needed to help following traffic make timely lane and speed changes.

It turns out the performance of our Echo and Prius are pretty well matched and agree with our real world experience. In the model, we counted the full-stop lights since we are "right on red" and experience has shown there is seldom enough traffic to force a full stop. Also, we used one cup as the estimated 'warm-up' fuel burn for the 1500 CC. engines of the Echo and Prius.

Handling

The car handles just fine but there are some quirks: (1) braking transition from regeneration-to-mechanical, (2) sub-optimal rear view mirrors, (3) instrumentation could be better. The brakes have a somewhat non-linear response that takes getting used to especially if braking hard, and a strange wierdness just as the car comes to a halt. Also, Toyota rear view mirrors are barely adequate so we anticipate an after market replacement. However, the cruise control and digital speedometer are outstanding.

The cruise control is easy to reach, 'instant on', and allows single digit, miles per hour adjusting by a quick tap. Furthermore, this car holds the speed with infrequent, 1 mph variances starting up a hill or going down. Sad to say but the online MPG reading is useless. Worse, the fuel level indicator is very inaccurate due to the fuel bladder that prevents tank vapor loss.

Going Down Hill
When going down a hill, the Prius will shutdown the gas engine and maintain speed using just the motor-battery. This avoids burning even idling gas:
In this photo, the green bar on the right hand shows "100 mpg" based upon turning off the engine going downhill. We've already seen the same pattern on the backside of the Parkway overpasses.
Camry Experiments
We bought this Prius to replace a 1991, manual transmission Camry that was damaged beyond Blue book repair value in an accident. But I'd just started experimenting with two new driving techniques that appeared to boost my city mileage from 32 mpg to 38 mpg: (1) conservation of momentum by early braking to a 'rolling when the red light turns green' and (2) coasting down large hills in neutral (illegal in most states and risky to automatic transmission cars.) The Prius automatically does both by regenerative braking to a stop, conservation of energy, and automatic coasting down hills.