And the best part, you can take your AWD Prius on Rally Races! Just kidding.

<Best Tank Economy!><Best Tank Endurance!>

Dumb question but why do you assume that an AWD will come with 2 electric motors?

yeah, prius AWD with a tiny bit more clearance would have us buying two, and my mom buying one too =)

That's how Toyota made the Highlander 4WD and same with the Lexus RX440h.

2001 Prius Photos       2005 Prius Photos
1992 Mitsubishi Delica Diesel-WVO Hybrid Photos

In the GH mileage database, the difference in mileage for the HH between 2WD and 4WD is not significant (even though it is ever so slightly higher for the 4WD). This may be for any of a number of incidental reasons, including locations, driving habits etc... For the FEH however, the difference in the GH database is significant, and the 4WD mileage is less than the 2WD mileage. This supports the contention that 4WD comes with a mileage penalty, which makes sense from an engineering perspective.
with 4WD, you have greater mass to accelerate/decelerate, and you have greater rotating masses as well, which sucks up more gas too (drive shafts and E-motor rotor, minimally). The regenerative braking argument does not convince me unless the changeover from e-brake to mechanical brake comes at a higher decel rate for the dual motor than for the single motor system, but I don't find that likely. Plus, the regen braking only contributes a very small part to the overall efficiency of the HSD, a much more significant part is the operation of the ICE under higher thermodynamic efficiency due to optimal engine loading.
Bottom line I would expect a 4WD Prius to be noticeably less efficient than a 2WD Prius. Personally, I don't see the point and would not be interested, although I could see how folks living in snow and ice territory coudl benefit from 4WD even at a mileage penalty.

The "penalty" for AWD comes from the mechanical losses and as stated the extra weight. In a AWD Prius, the back wheels would be driven by an extra electric motor (and a second set of batteries) as it is done in the HH and Lexus 400H. This both improves performance and, due to the increased available energy storage, better gas mileage. You shouldn't extrapolate from older designs of AWD in your analysis.

I would applaud a decision from Toyota that produced a AWD Prius as my only hope for an AWD hybrid that isn't a monster (or a Ford) is the promised one from Subaru.

I would be interested, but for a Prius that's going to go out into the boonies it should also have a decent-sized 12v battery and the ability to jump the HV battery from it (the way you can on the Ford).

I finally did a little further looking and in my mind, the 4wd Highlander just isn't a real 4wd. At least not to us rednecks...lol. It's definately a city vehicle for your typical suburbanite. Not something I would drive to camp on 10 miles of unpaved road in a foot of snow. It seems that is not what the 4wd system was intended for. The 4wd system on the Highlander is intended more for performance, because those are the only benefits that they highlight on the webpage. So, as for having an awd prius, the benefits would be mostly for performance and not utility. It'll help you in the snow, but only for short periods. So, the question is... what's the point? OHhhh, you have all wheel drive. If the snow's too much for you, stay home and stay out of my way.

I would buy an AWD Prius (as my second one). The purpose is:

1 - More energy storage for better gas mileage
2 - 4 wheel drive (My current Prius is 2-wheel drive as opposed to my previous Ford Probe which was 1-wheel drive - no traction control) for getting up my steep driveway in bad weather.
3 - Better acceleration (why not?)

As was said here it's not for off road use as the 5-inch ground clearnace is limiting.

ps: Its an interesting engineering project to add a battery, electronics, another computer (with info from the OBD2 CAN bus to know when to add or subtract torque) and two small hub motors to the rear wheels to do this as an aftermarket add-on.

I would have bought an AWD in a heartbeat when I traded my Outback for the Prius 3 weeks ago! Steep driveway, occasional need to navigate steep grass road by my barn made the Outback and previous Legacy great vehicles - I just wanted better fuel economy. Lot's of rain in the NW and occasional snow, as well as ski trips to the mountains also make an AWD vehicle desirable. Subaru indicated a year ago that it was developing a strong hybrid - I haven't seen anything recently.