The average car on the highway only needs about 14-20 horsepower to maintain 65mph. It is acceleration that needs the extra oomph. Once up to speed, a well calibrated electrical system would do amazing things. And the electric motors could easily do the job.
The problem isn't so much the electric motors, but how to use them.
In my opinion the best hybrids have not even been built yet.
What we should see is the following....
A small efficient diesel engine that is extremely light in weight turning an equally efficient alternator at whatever RPM the engine and alternator are at their most efficent state. In the rear, powerful electric motors that can accelerate quickly, but produce little or no drag when spun freely. In the front, lesser motors designed for maintaining speed, and most efficient for their size. Idling diesels are extremely efficient and even high powere alternators do not require tremendous power to turn even under full loads.
The motor always keeps a fairly small battery pack charged so that you can accelerate in traffic and cruise on the highway. Regenerative braking and cruise control that can use the downhills to also recharge the battery will be needed.
The stigma of the belching diesel is really no more. And small diesels are quite popular in europe. In fact, there are some Italian diesels and even 2-stroke gas engines that are producing almost unmeasurable polution in small displacements with NO added exhaust scrubbing.
Now, the drag race sets, and those that must be able to get to the next light in 4 seconds will find themselves in trouble, but the average driver would be fine.
If such technology were also coupled with 'smart road' improvements to prevent congestion and improve vehicle flow, you could see a tremendous drop in daily motor fuel use. Also, since high grade diesel and Home heating oils are the same basic formula, the yearly switch in refining would not occur. then, as oil sources dried up, the bio components could be added to offset the costs and allow that industry to build up.
Also, unlike true electrical vehicles, the on-board diesel will produce heat that can keep you warm in the winter, and it can be used to turn an AC compressor. I suspect that we would see taxes on these vehicles based on how many 'extras' are added that would reduce efficiency. Similar to the Gas Guzzler Tax today.
It isn't a long term solution, but one that would stretch our oil use under today's society into the later half of the century.
I know, I'm a fine one to talk driving around that huge truck of mine. But I only drive about 7,000 miles a year and it is far cheaper to keep what I have than to get something new. Had I known 10 years ago what I know today, I'd probably never have bought that truck, but hindsight is always 20/20.