Accordingly, three large bottles, five medium bottles or 10 plastic cups are equal to an hour-long bus ride with unlimited stops costs. However, they must be cleaned and cannot be squashed.
Currently, the fleet consists of 20 near-new buses, each with recycling bins and ticket officers whose duties include collecting any leftover bottles.
The Surabaya scheme has been a hit in the city of 2.9 million people, with nearly 16,000 passengers trading trash for free rides each week.
Authorities said roughly six tonnes of plastic rubbish are collected from passengers each month before being auctioned to recycling companies.
Indonesia, the world's second-biggest marine polluter behind China, has pledged to reduce plastic waste in its waters by some 70 percent by 2025 via boosting recycling, raising public awareness, and curbing usage.
Along with Surabaya, other parts of Indonesia are also trying to tackle the issue. Bali is phasing in a ban on single-use plastic straws and bags, while Jakarta is considering a similar bylaw to rid the city of plastic shopping bags.
