Those nagging "How" and "Why" questions about cars and all things related to cars abound. So how about a stab at some Q & A?

Q: Why haven't any of the automakers built a diesel hybrid? After all, diesel engines are inherently more efficient (better fuel economy) than gas engines. Wouldn't it make more sense to use them in a hybrid vehicle rather than a gas engine?

A: The problem is that a diesel engine, like an electric motor, is optimized for low-speed torque production. That's great for a truck or even a car, but not so good for a hybrid. The hybrid plays on the relative strengths of the electric motor, which provides low-speed torque for getting the car moving and for stop-and-go type driving. The gas engine provides high RPM power, for an extra burst of speed when passing and faster highway driving. Diesels also have unique emissions issues, which add to the cost and complexity of the drivetrain.

Q: How come modern economy cars don't get much better gas mileage than the economy cars of 10 or 20 years ago? Hasn't technology improved?

A: Yes, it has. But even though modern engines are more efficient than the engines of the past, they are also larger and more powerful. Today's buyers won't tolerate a car that requires 15 seconds or more to reach 60 mph. Accordingly, even "economy" car engines today are pretty strong, with 110-140 hp being typical vs. 70-90 hp 20 years ago. Also, today's economy cars are heavier, in part due to new safety equipment like air bags, and also because things like air conditioning have become standard, even on very inexpensive new cars. More weight and more powerful engines equal higher fuel consumption, even for an "economy" car.

Q: Whatever happened to "real" bumpers?

A: They're still there; they're just hidden behind rubberized decorative "fascias" -- the auto industry term for the body-colored front and rear panels that give new cars that bumperless look. This change happened for two reasons: One, the bumperless look is visually appealing to most people. Two, chrome plating is both expensive and environmentally toxic. So the automakers had two good reasons to shelve exposed chrome bumpers in favor of those body-colored fascias and hidden bumpers that don't have to be chrome plated.

Q: Why do many front-wheel-drive cars still have a driveshaft "tunnel" on the floorboard?

A: One of the design advantages of the FWD layout is the entire drivetrain -- engine, transmission and axle -- are packaged together up front, eliminating the need for the hump in the floorboard that divides the interior space of the cabin. But modern cars also sit very low to the ground. Thus designers have found a new use for the "driveshaft" tunnel as a place to tuck the exhaust pipe and other components so they don't scrap the ground. The downside is the "flat floorplan" (and more usable interior space) you'd normally get as a benefit of the FWD layout is sacrificed.

Q: It says "4WD" on the bumper, but there's no low range. What gives?

A: Technically, both the increasingly popular all-wheel-drive systems found in crossover vehicles and the traditional truck-style four-wheel-drive systems with high and low range are both 4WD. Both systems do, in fact, drive all four wheels at least part of the time. But the marketing of all-wheel-drive as 4WD is a bit deceptive, since that term has traditionally been used to refer to a truck-style system with two-speed transfer case and high and low-range gearing. From a marketing standpoint, "4WD" might sound more masculine than "AWD," which is why several automakers describe their lighter-duty AWD systems as "4WD." It's technically accurate, but also a bit confusing. Before you buy, be sure you know what you're buying and that it meets your needs, no matter what it says on the bumper.

Q: Have doors been getting higher? Or are seats getting lower?

A: Both. If you're old enough to remember the cars of the '80s and before, you may recall that you could roll the window down and comfortably rest your arm on the sill on warm sunny days. That is increasingly hard to do on most new cars. Why? In order to improve occupant protection in a side-impact crash, doors have been "built up" so that more reinforced steel and less glass is between you and that SUV that just ran the red light. There are also design considerations having to do with the placement of side-impact air bags. You may not be able to rest your left arm on the door as you drive -- but you'll be safer if someone T-bones you at an intersection.

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