Hybrid engine tech is pretty fascinating, especially because of how simple the idea is. Take the otherwise lost energy from braking and under-utilizing the gas engine, and redistribute it so that you can use that energy instead where it is needed, during acceleration, while at the same time allowing the manufacturer to install a smaller, more efficient gasoline engine.
Most of the hybrid gas savings are seen around town in the city, and highway mileage, while still better, will be closer to that of a standard gasoline engine powered car. The reason why is because a gasoline engine is at its most efficient at closer to full throttle, and at steady speeds. The hybrid system can’t really do much at a steady speed on the highway, since the gas engine is already at the most efficient it will be running, so any gas savings on the highway will be from the fact that a hybrid will have a smaller gasoline engine than a standard car.
The reason city fuel mileage is better in a hybrid, is because of some of the tricks it uses to achieve that mileage. In the case of the Toyota Prius (and I imagine the civic is the same in this regard, since the insight was) the gasoline engine will automatically be turned off while the car is stopped, and only restarted again when needed. Since the electric motor is there, with batteries charged by both regenerative braking (slowing down the car by having the wheels spin a generator to slow down the car, in combination with standard brakes) and by having the engine itself run the generator in some circumstances (thus allowing the gasoline engine to be run at its most efficient throttle settings more often), pressing the throttle can result in the car being moved along at lower speeds just by the electric motor, and the car will automatically kick in the gasoline motor when it’s power is needed.
Think of the hybrid drivetrain as a rather ingenious method of reallocating otherwise lost energy from things like braking, and using it instead to move your car down the road.
If you can picture your cars efficiency doing city driving as something akin to a waveform, starting on zero as you are stopped, then moving gradually up as you start moving from a stop sign, gradually building up as your speed levels off, peaking while you are coasting along before braking, then dropping down to nothing as you burn off your built up energy by hitting the brakes, and venting it off as heat, you’ll get an idea for how a hybrid improves fuel mileage. Once you start braking, you would normally begin venting off all of your built up momentum and energy as heat in the brakes. A hybrid will instead turn the engine off at the stop sign, then with the energy gleaned from braking, assist the gasoline engine in accelerating the car, fattening up that efficiency curve. as your speed levels off and you start coasting, the electric motor stops assisting, and as you apply the brakes to stop, the regenerative braking system kicks in by allowing the brakes to be used less, and by instead slowing the car some by having it spin a generator. It’s a deceptively simple technology, it’s just that until recently we lacked the kind of computer power required to do it cheaply.
On the highway, a lot of the benefits are lost, since a hybrid system doesn’t add more efficiency for free, it is just giving you back energy you would have otherwise lost. On the highway, your gasoline engine is running at its most efficent anyways, and in that situation, the hybrid engine can’t help you get any better gas mileage than any other well designed gasoline engine of similar size. It will just give you a little extra kick in passing. The hybrid works by filling in the gaps where a standard gasoline engine is least efficient is all, so if you only intend on driving it on the highway, any small fuel efficient car will work well, and while your gas mileage would still be a smidge better due to the smaller hybrid engine, fuel cost wouldn’t be a reason to choose one in your case.
It’s an awesome piece of technology, and if you lived in an environment with more stop and go driving, where the benefits would be dramatic, I’d go for it (I wouldn’t mind one myself) but on the highway, the benefits are essentially wasted.
I expect in the future we will see hybrid engines become rather common, as it is simply too good of an idea not to implement, that even has benefits for performance cars, as anything that increases efficiency will also let you make more power (or in this case, use otherwise lost power where you want it)
