In the present scenario, the energy crisis is one of the main challenges in the real world. The fossil-fuel resources are being depleted at a tremendous rate due to their excessive consumption. This has put forth the widespread assumption that if resources are being used at the current rate, the time is no longer when all our resources will expire. Thus, there is a need to develop technology that saves energy from getting wasted. Traditionally, regenerative braking with the ability to generate energy has been promising, but the amount of energy saved was highly insignificant. A considerable amount of energy, which is generated by the engine, is lost while braking even in case of regenerative braking. The regenerative braking involves direct conversion of the Kinetic energy to Electrical Energy; however, a promising alternative is present while storing the Kinetic Energy of the Vehicle in the form of Mechanical Energy of a rotating cylindrical flywheel. This paper states the advantages of storing the Kinetic Energy of the Vehicle in Mechanical form rather than direct conversion. For the design of this kinetic energy storing device, some calculation has been done for the vehicle at different resistance load, torque, speed, and calculation for selection of the planetary gear, design of flat spiral spring is considered and also using SOLID WORK software some parts of the system are designed. By taking the velocity of the vehicle from 8.34m/sec to 27.8, the kinetic energy loss of the vehicle is increasing with the increase of velocity, but the efficiency of the kinetic energy recovery system will decrease. Braking the vehicle with the velocity of 8.34m/sec has 219KJ of kinetic energy loss, and energy stored by flat spiral spring is 201.4KJ, and the system has efficiency of 91.9% and can save 0.00464L of fuel from 0.005L which will be consumed at 8.34m/sec. But the vehicle moving at 27.8m/sec, the kinetic energy loss is 2434.4KJ, and the stored energy is 201.4KJ, and the kinetic energy recovery system has efficiency of 8.3%. So, using flat spiral spring kinetic energy recovery is useful and recommendable for the vehicle, which has a high stop and goes times.