Basically Motor class of policies like Marine insurance(transit Insurance) till some time in the recent past were goverend by Tariff rates, and presently on specified guidelines.
Based on several risk factors they decide the premium:
1. Type of usage: Private / commercial
2. Registered under which zone: A,B,C,D
3. IDV- Insured Declaraed Value /Sum Insured of the car
Car ins new / 2nd hand
4. Type of cover opted
5. Age, sex type of car, number of miles driven per year and more.
this is how the premium is fixed depending on the risk per case basis.