TECHNICALLY, it's against the rules, but thousands of Melburnians are using their myki card on the city's trams, despite it being valid for travel only on trains.

Leaked government data logs obtained by The Age show that travellers with myki cards have used the system on trams 41,000 times over the past fortnight, including almost 5000 times last Friday.

No one has been booked, let alone fined, even though the $1.35 billion smartcard - originally intended to replace Metcard in 2007 - is legally valid for use only on trains in Melbourne. To become valid on trams and buses, a new law must be gazetted.

The troubled smartcard system has shown signs of improvement: the leaked data shows it worked 96 per cent of the time on trams in May.