How to get people to understand that braking is the #1 cause of bad city mpg.

Gaining speed before the hill helps, it does not remove the fact that the incline adds energy requirements. In effect, I linearize the power demand over a longer distance.

I think of it this way: if I start adding power before the hill, what is the average power I will need to arrive at the top of the hill at the speed I want ? For me the answer is gained from experience -- there is NO WAY I can solve that in my head

My Prius vagon has a power meter display that splits the 'ECO' ICE power into four bars, and then I think another two or three bars of 'POWER' ICE. For the mountains I drive, I bump up the ICE to 3 or 4 bars (still in the ECO range) far enough ahead of the incline to reach about 70 - 75 mph when the incline starts. I then stay at 3-4 bars of ICE all the way up. I still might lose speed, but if I planned right the speed drop is acceptable. What do I gain ? Avoidance of high rpm bursts, and a constant power that gives the car time to optimize the gearing.

There are practical limits to this game, of course. I avoid speeds over 75 mph before the incline to not confuse other drivers, to not risk speeding tickets, and because I guess that the added aero friction has wiped out the savings from an average lower rpm.

 

The car provides the value of miles/gallon either in the HSI or more accurately using a Scan Gauge. All mechanical factors such as friction are included since the mpg reading is based on the actual gas used per mile. So for that mile whatever the mpg is determines how much gas you use. If you can go faster at higher mpg that's nice. Generally faster gives lower mpg.

 

I frequently climb mountain grades many miles long, one is a 7% grade for 7 miles. Dropping to 20 mph means a huge increase in travel time, very unsocial and unsafe speeds on multilane highways, and a seriously illegal delay of traffic on the single lane roads. And all this for what the GenIII BSFC (brake specific fuel consumption) charts shows is a surprisingly small reduction in ICE efficiency.

Climbing requires more energy and fuel, that is just a basic requirement of physics. The Prius ICE has a wider efficient operating zone than other cars, and GenIII is even better than GenII. They provide that extra power fairly efficiently, even when the HSI breaks into the PWR zone that the car knows is unnecessary on flat ground. That extra energy is stored as 'gravitational potential energy', and is not truly wasted until descending the hill. If the hill is not too steep, i.e. 1-3% range, the skilled driver can 'recover' it by judicious gliding. Only on the longer steeper hills, where much of the energy must be thrown away as brake friction or engine compression braking, must that climbing energy be truly lost.

So don't be afraid to go part way into the PWR zone to climb. For better detail, find the BSFC chart, note the maximum RPM associated with the amount of efficiency reduction you can tolerate, then watch RPM on a ScanGauge while climbing. Somewhere in the 3000 - 3500 - 4000 RPM range should give acceptable efficiency with far better driveability than you are getting now.

 

exactly

 

So long as potential energy gained on a climb can be used on the downhill I don't think there need be much of a hit to fuel economy on hilly round trips compared to flat roads. I suspect that some, or perhaps a lot, of the bad reputation of hills comes from drivers who do not drive with load (DWL) on the uphills. Put another way, the fuel economy hit if present is from the transmission 'gearing', not the ICE.