Brakes are something we seldom think about. They have become so reliable and sophisticated that we know they can stop the vehicle smoothly every time. It wasn't always the case. When Henry Ford first started building cars, the brakes were applied by a series of rods and links between the pedal and each wheel. Even when adjusted as accurately as possible, the mechanism was tricky and unbalanced, causing some wheels to brake more than others. Bringing the vehicle to a stop could be a handful for the driver.
Hydraulic brake systems were a huge improvement, as it allowed equal force to be applied to all the wheels for more even braking. In the mid 1960's, braking systems took another leap forward as most vehicles became equipped with split braking systems. These systems used two or more hydraulic channels so that if there was a leak on one channel, the vehicle still had brakes on the other channel. Some used a front to rear split — more common on rear wheel drive vehicles —while many front wheel drive vehicles used a diagonal split so that at least one front wheel would brake if a channel leaked.
Disc brakes started to become common in the early 70s, and they provide more consistent braking than the older drum brakes. Disc brakes can dissipate heat rapidly so they can withstand repeated applications better. Anyone who has attempted several fast stops with older drum brakes will know that they quickly fade, which means that no matter how hard you step on the brake pedal, braking force keeps getting less and less — not so good when you need to stop a trailer on a long downhill grade.
The next big improvements were the introduction of antilock brakes (ABS) in the 1980s. Antilock brake systems use a computer to rapidly cycle the brake system between apply and release if a tire is starting to lose traction. The big advantage of ABS systems is that they allow each wheel to maintain maximum braking force even under slippery conditions so that the vehicle can be stopped under control and the driver even maintains steering control while braking.
In recent years, braking systems have been refined, with the addition of other vehicle systems such as traction control, stability control and roll control. All these use the brake system to help drivers maintain safe vehicle control and do it without the driver having to do anything special. I call them equalisers, because they can provide car control ability to novice drivers equal to skilled drivers. Another refinement has been brake assist. This system uses the power brakes to apply full brake force if the driver quickly steps on the brake pedal. Research has shown that when drivers react to an emergency situation by braking, they quickly step on the pedal but don't apply full force till a second or two later. That short time frame of delay in full braking can make 2 or 3 vehicle lengths difference in stopping distance - the difference often in preventing a collision or having one.
There is another method of braking too. Its often called "engine braking". When you back off the throttle, the engine becomes a big air pump and the force it takes to drive that pump comes from the drive wheels and the vehicle is slowed. You may have heard of "Jake" brakes or exhaust brakes. These are systems that restrict exhaust gas flow to make engine braking more effective. On Semi's you often hear the brap-brap-brap as they decelerate using a "jake brake". Modern diesel pickups use the turbocharger design to restrict exhaust on braking, so it doesn't have that annoying brap - brap sound.
Most automatic transmissions are designed to freewheel in Drive range, so many drivers are not familiar with engine braking, but by selecting a lower gear range or using special features such as Tow/Haul mode found on many trucks, automatic transmissions can provide engine braking just like manual transmissions do. This is extremely useful when hauling a heaving load or towing a trailer on long downhill grades, as it enables the driver to keep vehicle speeds down and then using the regular brakes only occasionally to maintain the slower speed. Heat is the biggest enemy of brake systems and continuous application of brakes can cause them to overheat and fail, so using additional engine braking is the smart way to go.