How to keep petrol price low while easing burden on subsidy

Introduce prepaid petrol!
Make it just like prepaid line for mobile.

Every car will have a prepaid card registered with it.
The card value can be topped up once a month.
The card will have limited discount value i.e. 120 litres of petrol.
Price of putting in this 120 litres would be same as buying petrol from the gas station, * MYR 2 per litre.
The card would need to be swiped each time when we pump petrol, so we won't get charged.
When the card value is used up/without the card, the petrol is at MYR 5 per litre.

How does it sound like?

It could also help to reduce traffic congestion on the road.