So, when I drive to work in the morning in bumper to bumper stop and go traffic that barely gets up to 10mph for large stretches, will my TCH run on gas or electric? I really do need to read more about the HSD before I actually get my TCH.

I don't think you'll need to study up. In 10 miles per hour driving you should be on battery most all of the time. Unlike the other post where they get up to 40 (possibly quickly) between lights your ICE won't have to run much in really slow moving traffic (except to charge the battery every once in a while if it's for a long period of slow driving)

Your TCH will run mostly on electric - sometimes for over a mile if you accelerate gently and coast in bumper to bumper traffic at speeds under 20MPH. I currently have a FEH (and soon a TCH as well) and it is amazing how quiet it is when creeping along in bumper to bumper traffic on electric power.

Like C said.
All the EV capability still ultimately comes from running the gas engine- so a lot of stop/go will require the engine to come on more than a 'moderate' amount of it. Also, accelerating in the manner many Americans are accustomed to will cause the ICE to come on even at low speed, negating some of the EV benefit and eroding FE. C definitely appears to like driving 'normally' I like his mention of 'suburban' driving.

Balthasar- not trying to imply IMA is inferior (look at my car). Just different. And of course, the genII IMA is a different animal, sort of. Good point about using the acceleration as the point of difference.

ASSUMING:
- the engine is up to operating temp, especially the emissions controls (catalytic converter).
- the battery has enough charge to do the job. Which it will not after a few minutes (causing the engine to come on).

Do not expect it to be 100% electric 100% of the time even when crawling- it won't, depending on the above conditions among other things.

Good point. In actual usage in bumper to bumper traffic on I-15 in San Diego, I find the FEH will go a mile or more on electric, then about 1/4 mile on gas as the battery recharges. My mileage goes up when driving in these conditions!

good points. i think ken's question relates to the epa mileage estimates on the prius. he wants to know, if what you're saying is correct (and it is), why are the epa city mpg estimates for the prius higher than the highway estimates. i don't have concrete evidence, but i believe that the reason may be that hybrids get a bit of an unfair advantage using the current epa testing methodology. the simulated city driving benefits from the battery being fully charged. when the epa test ends, the battery has not been returned to its fully recharged condition, ergo they kind of got something for nothing. as mentioned on this board, it would be a more fair test if the battery had to be returned to fully charged by driving by the end of the test.

Thank you for comments.
I also think it is unfair if the EPA tests use up the fully charged battery.
The Japanese 10-15 mode test requires the same SOC level between start and end of the test.
I believe the EPA test is done the same thing.
So, I think the HSD(THS) system has a lot of advantages and possibilities for the city driving.

Ken@Japan

You all know that the EPA itself does not test most cars, correct? They let the OEMs test their own cars and then spot check the results....

Thank you for comments.
However, I think it is dangerous to say "All cars, including the Prius" about city driving.
As you know, the EPA city mileage number is better than highway among HSD(THS) vehicles.
The below chart is the test schedule and it describes a lot of start-stop conditions. In addition to that the city test is done from cold start while the highway test is done with warm engine.
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

As I posted on others, I think the HSD(THS) system has a lot of advantages and possibilities for the city driving and your theory is not always true.

Ken@Japan

OK, if you want to get technical, I should have said that I get worse city mileage than highway when driving a Prius, Civic Hybrid, Camry Hybrid, or any other car, and most if not everyone I know of gets similar results.