Plug-in Hybrids Compared

Plug-in hybrid electric vehicles (PHEVs or plug-ins) are receiving a lot of attention in Washington, in the media, and among automakers. Here at AFS Trinity we are asked often how vehicles that will use our Extreme Hybrid™ technology would compare with other hybrids on the road today. We are pleased to provide the following comparison.


The Toyota Prius was a pioneering hybrid vehicle and it is still viewed as the leading hybrid car in the world. Plug-in conversions of the Prius have been created by non-profit enthusiasts and small private commercial converters without the involvement of Toyota Motor Corporation, and they are doing a great job in most respects demonstrating the potential of this technology to the public. However, the Prius was not designed to be a plug-in hybrid, and inside its Hybrid Synergy Drive there is a planetary power splitter “transmission” that limits the top speed that a Prius can go in electric-only mode to 34 mph. The plug-in conversions of the Prius have the same attributes and limitations of the car on which they are based— 34mph is their top speed in electric only mode, which means that they must run their gasoline engines whenever driving at highway speeds and, in fact, any time they exceed 34 mph.

The graph below shows that for a typical weekly drive cycle, the Prius conversion plug-ins would be limited to about 100 miles per gallon unless their drivers stayed below 34 mph nearly all the time, which, for most drivers, is of course impractical. In fact, the U.S. Department of Energy estimates that the average American drives at highway speeds 45% of the time.

AFS Trinity Concept Car - Front

* Drive cycle is 300 miles in one week, consisting of 40 miles on each of 5 days and 100 miles on the 6th day. We assume the battery is charged by plugging it in each night.

This statistic combined with others that the US EPA and US DOE have collected about American driving habits leads one to the inescapable conclusion that, for plug-in hybrids to be truly practical and achieve their full potential in reducing dependence on oil, they must be capable of being operated in electric-only mode for up to 40 miles per day, thereby meeting the weekday driving needs of 75% of Americans, and they must also be capable of being operated in electric-only mode, not just at 34 mph or less, but at all typical driving speeds, including highway speeds of at least 55 mph.

Here are links to the web sites for other plug-in hybrids under development mentioned in the discussion above:

Daimler Chrysler Sprinter Van
EDrive Systems, LLC