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."

In March Transport Minister Andrew Constance sought to end Opal running by increasing the number of "transfers" needed to qualify for one journey from three to seven. A transfer occurs when a user travels multiple times on the same mode of transport in the one journey within the same hour.

Before the changes in March, it would take Mr Lo about 1½ hours to chalk up the necessary number of trip transfers.

He travels up to five times a week from his home in Campbelltown in Sydney's south west to the UNSW campus at Kensington.

And the hours he spends on Mondays walking between stops in Pyrmont to tap his Opal card on and off saves him about $20 a week.

The latest government figures show that while the amount of Opal running has fallen substantially, the measures announced in March aimed at stamping out the practice have yet to dissuade everyone.

The number of short trips taken at Sydney's Opal running hotspot at Pyrmont fell to 11,935 in the five weeks to the end of July, down from 63,636 in the same period to March 6.

Mr Lo said he had observed a change in the type of people who were Opal running since the changes in March.

"I have seen a noticeable drop off in the average Joe Bloggs doing it. It used to be office workers but now I notice it has changed to fitness fanatics – they see it as a challenge," he said.

Last Monday, Fairfax Media counted about a dozen people Opal running or walking between the two stops in less than an hour. Some were swiping several Opal cards.

One runner, who declined to give his name, said he ran between the two stations at Pyrmont to save himself about $8 a week.

"I am a student – anything I can get is worth it," he said.

But Mr Lo and other diehard Opal runners will reconsider the practice next month when free travel after eight journeys in a week is replaced by half-price travel, reducing the incentive to run or walk between stations to swipe their cards.

"Right now it is still doable," he said.

The intention to close the loophole in March was an about-turn on former transport minister Gladys Berejiklian's call for commuters to "beat the system" and "find the savings".

Transport for NSW said the changes to combat Opal runners had "significantly impacted fare cheats with data showing falls across the network hot spots".

"The set of Opal system changes was introduced to disrupt the various versions of Opal running, a form of fare rorting, taking place at light rail stations in the Pyrmont and Paddy's Market area and between some train station," a spokesman said.

"The changes had an immediate impact on those fare rorters running or biking between train stations or light rail stops."

The department said the stretch between Macdonaldtown and Erskinville train stations was no longer an Opal hotspot.

Another favoured spot for Opal runners has been in the CBD on the light rail line between Capitol Square and Paddy's Market.