Five months after the Baird government moved to close a loophole in the state's electronic ticketing system, people are still "Opal running" between light rail stops to gain free travel on public transport.

And the Opal run of choice remains 300 metres between stops on the inner west light rail line at the Star and Pyrmont Bay in central Sydney.

University of NSW student Lawrence Lo spends up to four hours on Mondays walking between the two stops to swipe his Opal card in order to qualify for free travel later in the week.

"It is a challenge that rewards," he said. "It is how the system is programmed and we are just using one of the provisions in it."