its a card that get pasted on the windscreen........its has stored information of ur car....and u have to put amount in it like u guyz upload credit in ur mobile...only difference is kei u have to get this uploaded from the booth they have before toll plaza...and then you just pass from the express lane...there is a sensor on top which scans the card automatically and stores the data of ur entrance....wen u exit from motorway thru express lane...then card is scanned again automatically and the amount to be paid is deducted from the balance that u have uploaded....
if u get a challan then they will scan the card and add the fine amount....which will be cut with the normal toll at the toll plaza while going thru express lane via e-tag card.