NEW YORK ( TheStreet) -- Electric and small cars be damned! Why bother with them when you can now get 45 miles per gallon in a large luxury Mercedes sedan -- the E 250? I put 250 miles in a week of driving this previously impossibly efficient combination of automotive specifications. Here is what I found. Before we get started, let me just say that nothing beats the smoothness, silence and overall zen feeling of driving an electric car. One-pedal driving and the simplicity of the mechanical driveline makes for the lowest maintenance and highest reliability, too. But what if, for whatever reason, you just don't want to buy some form of electrified car? In order to achieve both the best fuel economy and get the most amount of low-end torque, you need to drive a diesel. Volkswagen, Mercedes and BMW pioneered the return of the U.S. diesel for the 2009 model year. The U.S. diesel market basically breaks down as follows: 1. One the one hand, you can buy a four-cylinder diesel, best represented by VW, Audi and, most recently, Chevrolet, Mercedes and BMW. Of these four-cylinder diesels, only the VW Passat is a large car, and it can't be had with four-wheel drive. 2. On the other hand, you can buy a six-cylinder diesel. These are available from VW, Audi, Porsche, BMW, Mercedes and Jeep. They are typically the larger, heavier and more luxurious cars -- and the fuel economy is naturally less. In this expanding field of diesel cars sold in the U.S., the Mercedes E 250 stands alone as the only large luxury sedan, available with optional four-wheel drive, using a four-cylinder engine. Thanks to this lighter and more frugal engine, the Mercedes E 250 delivers 45 mpg on the highway in two-wheel drive, and 42 mpg on the highway in four-wheel drive. City MPG in four-wheel drive is 27. Think about it: If you are taking a road trip, cruising on the freeway at 70 miles per hour, you will be getting almost the fuel economy you would obtain in a Toyota ( TM) Prius, and that is in a large Mercedes luxury sedan. Not bad, huh?