Explain the function of regenerative braking and its impact on overall energy efficiency.

Regenerative braking is a braking method that recovers kinetic energy (energy of motion) during braking and converts it into a form that can be used or stored, instead of dissipating it as heat as in traditional friction braking. During regenerative braking, the traction motors on the train or locomotive are used as generators. When the driver applies the brakes, the motors are switched into a generating mode. As the wheels slow down, they turn the motor rotors, which generate electrical energy. This electrical energy can then be used to power other onboard systems, such as lighting, air conditioning, or auxiliary equipment. Alternatively, the energy can be fed back into the overhead catenary (the electrical power supply for electric trains) or stored in onboard batteries or supercapacitors for later use. The impact of regenerative braking on overall energy efficiency is significant. By recovering and reusing energy that would otherwise be wasted as heat, regenerative braking can reduce the energy consumption of trains and locomotives by a substantial amount, often ranging from 10% to 30% or more, depending on the operating conditions and the specific system implementation. This reduction in energy consumption translates into lower operating costs, reduced greenhouse gas emissions, and a more sustainable railway system. Regenerative braking is particularly effective in situations where trains frequently accelerate and decelerate, such as in urban transit systems with frequent stops. For example, a subway train that regenerates braking energy every few minutes can significantly reduce its overall energy consumption compared to a train that relies solely on friction brakes.