At one time, if you wanted a vehicle with four driven wheels, you were limited to just a handful of large trucks and full-size SUVs, most of which were used for work chores or off-road adventure.

But times have changed. Now 45 percent of new vehicles sold in the U.S. are equipped with either all-wheel drive (AWD) or four-wheel drive (4WD), according to an Edmunds analysis of IHS Markit data. For vehicles that have AWD or 4WD as an option, 61 percent of buyers choose a model with either. In states with cold and snowy winters, this "take rate" is 90 percent or higher.

So the popularity of vehicles that can send power to both the front and rear wheels is indisputable. But what's the difference between AWD and 4WD? And which is right for you? AWD vs. 4WD terminology can sometimes be confusing, especially since AWD systems have become more robust and 4WD has gotten more sophisticated, blurring the distinction between the two. Adding to the confusion, various manufacturers often use these terms differently.

Here's how each system works and the advantages and disadvantages of each. With this knowledge, you can make an informed decision when shopping for your next family SUV, midsize SUV, car or truck.

AWD vs. 4WD

AWD vs. 4WD: All-wheel drive, which the Subaru Forester has, provides the fewest compromises in ride and fuel economy on dry roads and delivers increased traction under normal winter conditions or light off-roading. Four-wheel-drive systems, like the one on the Jeep Wrangler Rubicon, tend to be more robust and can generally handle more rugged terrain.

What Is All-Wheel Drive?

As the name implies, all-wheel-drive systems power both the front and rear wheels all the time. But in practice, there are actually two types of drivetrains that are called AWD. One does, in fact, drive all the wheels continuously, and some manufacturers refer to this as full-time AWD. The second, often called part-time AWD or automatic AWD, operates most of the time in two-wheel-drive mode, with power delivered to all four corners only when additional traction control is needed.

How Does All-Wheel Drive Work?

AWD systems, both full-time and part-time, generally operate with no input from the driver, although some offer selectable modes that allow a degree of control over how much power goes where. All the wheels get torque through a series of differentials, viscous couplings and/or multiplate clutches, which help distribute power to the wheels so that the car's traction is optimized. The vehicle still operates smoothly under normal conditions.

Full-Time AWD

In full-time AWD, both the front and rear axles are driven all the time. On dry pavement, this kind of AWD can help the vehicle handle better and ensure that full power gets to the road. And in slippery conditions, such as ice, snow or mud, it provides additional traction for safer, more confident handling.

Part-Time AWD

In normal operation, part-time AWD sends torque to two driven wheels, either the front or rear, depending on the make and model. The system then automatically engages the other two wheels when road conditions demand extra traction. Modern part-time AWD uses an array of electronic sensors that feed information to a computer, which controls the amount of power directed to each wheel.

All-Wheel-Drive Pros and Cons

The best thing about AWD is that the driver doesn't have to make any decisions about engaging the system. Either all the wheels are being driven full time, or the system itself is designed to sense loss of traction and send power where it's needed. AWD is available on a wide variety of vehicles, from compact sedans to performance models to all sizes of SUVs, giving you a broad range of choices.

While AWD is able to work well in a variety of conditions, from rain to snow to light off-roading, it's generally considered a lesser choice by serious off-roaders. This perception is changing somewhat as modern AWD systems get better and more capable, but many drivers who like to venture far off the beaten path still prefer to decide for themselves when to engage four-wheel drive. AWD also increases the cost of a vehicle and, in most cases, will reduce fuel economy.

What Is Four-Wheel Drive?

This is the more traditional system that comes to mind when most people think of drivetrains that power all four of a vehicle's wheels. It isn't surprising since the principle goes back almost to the beginning of motorized transportation. The stereotypical picture of a 4WD vehicle is of a truck with high ground clearance, a shielded underbody, tow hooks and big, knobby tires. And it's true that this system is still found primarily in large trucks and SUVs.

But through the years, 4WD engineering has become increasingly sophisticated, and although it generally remains capable of more serious off-road use, it can now be found on a wider variety of comfortable, even luxurious, models. 4WD systems deliver torque through a series of front, rear and center differentials, transfer cases and couplings, which allow the vehicle to operate at maximum traction under a variety of conditions.

How Does Four-Wheel Drive Work?

Like AWD systems, 4WD is designed to send torque to all four of a vehicle's wheels to increase traction when needed. But 4WD systems tend to be more robust than AWD ones and can generally handle more rugged terrain. And they, too, come in two types: full-time and part-time.

Many 4WD systems also have low and high ranges that can be selected by the driver, either with an electronic switch or a floor-mounted mechanical lever. The low setting provides maximum traction in an off-road environment, while the high setting is the default configuration, useful for slippery on-road conditions, such as packed snow, ice, loose sand or gravel.

Full-Time Four-Wheel Drive

Full-time 4WD operates as a full-time AWD system does, with all four wheels receiving power on a continuous basis. In some designs, the driver may have the option of controlling how power is apportioned to the front and rear axles through selectable modes.

Part-Time Four-Wheel Drive

This type is the real traditionalist of four-wheel propulsion and can most often be found in trucks and SUVs that are designed to work and play in more extreme conditions. In this case, the vehicle is typically driven by two wheels, most often in the rear. The driver needs to make the decision to engage 4WD when needed and either push a button or shift a lever. Some systems also allow the driver to lock the vehicle's differentials for extra traction in extreme off-road conditions.

Four-Wheel-Drive Pros and Cons

4WD vehicles are generally best at handling adverse conditions, both on road and off. Even though these systems are now available in well-appointed luxury trucks and SUVs, at heart they still tend to be designed for ruggedness and maximum pulling power, and they are well-suited for work and play in difficult terrain.

These days, 4WD design has become increasingly refined, as has the design of the vehicles that can be ordered with it. But, depending on the make and model, 4WD still often delivers a stiffer ride than 2WD. These systems also have a detrimental effect on fuel economy and increase the initial cost of the vehicle.

AWD vs. 4WD in Snow

A couple of things to keep in mind up front: Whether you choose AWD or 4WD, any vehicle can lose traction and spin out if pushed hard enough. And while both systems are designed to increase traction by engaging the front and rear wheels, neither helps you stop better. Having said that, both AWD and 4WD can give you a significant advantage in snowy and icy conditions and may be worth the extra cost, depending on where you live and how you use your vehicle.

Driving in cold weather often means encountering a variety of rapidly changing road surfaces, from soft snow to hard-packed snow to glare ice. AWD systems, which deliver power to all four wheels all the time, or automatically engage four-wheel torque when needed, are best at dealing with these changing conditions. They take the guesswork out of the equation and can act more quickly than a driver to handle variable road surfaces.

On the other hand, 4WD is generally well-suited to navigating deeper snow or other more extreme winter conditions. It can get you unstuck from a snowdrift more easily, manage icy hills more effectively, and get you to work safely before the roads are plowed.

Do You Need AWD or 4WD?

Unsurprisingly, the answer to the AWD vs. 4WD debate is that it depends on where you live and what kinds of driving conditions you encounter, as well as personal taste.

AWD can be found in cars, trucks and SUVs of all sizes, from compact to full-size, giving you the widest possible range of vehicles to choose from. It delivers increased traction under normal winter conditions or light off-roading and provides the fewest compromises in ride and fuel economy on dry roads. And it has the advantage of either powering all four wheels on a continuous basis or automatically controlling which corner gets the torque, taking the decision-making process out of the driver's hands.

4WD might be the better choice for those who live in remote areas, need to work in extreme weather conditions, or enjoy off-road adventuring. This system often comes in trucks and SUVs with higher ground clearance than average, making them well-suited to managing deep snow, rocky terrain and steep grades, as well as carrying or towing heavy loads. In addition, the models with part-time 4WD and low- and high-range features give the driver the greatest amount of control over where and how the power is delivered.