The exhaust system consists essentially of several tubes of different shapes, each tube being designed to be connected to each other and each shape conforming to a particular portion of the underside of the vehicle. (The pipes are often bent to wrap or otherwise accommodate other nearby components of the car, such as axles.) Each pipe is responsible for moving the exhaust gases backwards, but many parts are dedicated. In other words, from the outside, the system looks like a bunch of connected pipe sections that extend from the engine compartment to the rear bumper, but some of the pipes play an additional role in the flow of exhaust through a particular pipe.
For example, a Y-tube (simply, a Y-tube) can be installed such that the end with two openings is bolted to two corresponding openings in the exhaust manifold to incorporate waste from the engine into the system. Alternatively, when installed at the rear end of the car, the Y-tube can help create a dual exhaust system with an exhaust pipe on each side of the car (for a often popular sporty look). The middle tube may be connected to a muffler or resonator, which is another important system component (we will be introduced on the next page). The balance tube in the dual exhaust system helps to equalize the exhaust pulse traveling under the driver's and passenger's side. The air gap tube is a specialized nested tube that acts as a heat shield and insulator by providing an additional layer for the airflow.
And the tail pipe, which is typically peeking out from underneath the rear bumper, usually has a larger opening and might be made of more substantial-looking metal, to give the appearance of a performance exhaust that's a common feature of high-end cars.
Though it might seem inefficient to have a ton of pipes instead of just one, really, all those segments serve a purpose. For one, bending pipes is hard work, and it's easier to connect small angled segments to straight pipes than it is to shape one long, expensive, heavy pipe to fit every contour of a car. Also, exhaust system components wear out at regular intervals (depending, of course, on the manufacturer, its materials, driving conditions and environmental factors). It's easier and less expensive to replace one rusted-out segment of pipe, banged-up muffler, or worn-out catalytic converter than it would be to install a whole new system.