D.C. series motors are commonly used as traction motors in electric vehicles, locomotives and trams because of their high starting torque and simple control characteristics.

High Starting Torque: The series connection of the armature and field winding in a D.C. series motor results in a high starting torque, making it ideal for applications where high torque is required to get the vehicle moving.

Simple Control: The speed of a D.C. series motor can be easily controlled by varying the applied voltage, which makes it simple to use in traction applications where the speed needs to be varied to match the load.

Reversibility: D.C. series motors can be easily reversed by changing the direction of the current, making it useful for traction applications where the direction of travel needs to be changed frequently.

Durability: D.C. series motors are rugged and durable, and have a long service life, making them ideal for traction applications where reliability is important.

Overall, D.C. series motors are an economical and efficient solution for traction applications, and their simplicity, reliability and high starting torque make them a popular choice for electric vehicles and other traction applications.