What do I look for on the screen

What? I am still shopping for my first Prius and was under the impression that when stopped in traffic nothing is running except to take care of power needs for A/C, etc. and thus much better mileage under stop and go conditions. Have I got that wrong?

 

Yes, you have that wrong. Like any car, the Prius gets better mileage when it's moving. Look at the limiting case of standing still - in that case the best you can do is zero miles per gallon because you are not moving.

Why many people think the Prius gets great mileage in stop and go traffic is because it gets great mileage compared to a normal car. Normal cars get incredibly poor mileage in stop and go traffic. The Prius still gets pretty good mileage in stop and go, but not as good as driving along at a modest speed.

Tom

 

:welcome: Welcome to PriusChat, libby724 and Lhunterdds!

To expand a little on what Tom said, in a conventional car in stop-and-go traffic, the Internal Combustion Engine is always running, so you are burning fuel even if you're not moving; in the Prius, the ICE shuts off, so while you're not going any miles, you are also not using any gallons, but your mpg is still zero or low. When traffic does go, it takes energy to get either car moving, but in the Prius you haven't wasted all that fuel while you were stopped as well. If traffic is just creeping, not jumping up to 20 mph and then stopping again, the Prius can gently move on battery power alone, until the battery discharges to the point the ICE must run to recharge it. All power comes from the ICE, the battery just smoothes out the power demand.

The key to getting good mpg is to use the ICE to accelerate at it's best power output, which means no arrows to or from the battery (the pulse), to a cruising speed, and then rolling with no arrows at all until your speed drops to the point you need to accelerate again (gliding). That's the ideal situation, which is frequently impractical if there's any traffic or hills. Also, the way the ICE and two motor/generators are connected, the ICE must turn above 42 mph, so best mpg is under that speed. The faster you go, the more energy it takes to get up to speed and stay there.

On top of all this, the Prius was designed to be a low emissions car, so the first five minutes after you put the car in READY are spent getting the ICE, exhaust system, and catalytic converters hot. To do that, the ICE runs rich, using more gasoline. So a 10 minute run to the store, stop and park 10 minutes to shop, then another 10 minute drive home will use more gas than a 30 minute drive. If you have many errands, drive to the farthest one first to get the ICE nice and hot, then work your way back.

All that being said, you'll still get better fuel efficiency in a Prius than any conventional car, without even trying.

 

Thanks for that informative post, Bill. I also wasn't sure what the ideal acceleration mode was for the Prius.