Huge demand for a cheap German railway ticket that was offered to ease the cost-of-living crisis led to savings of almost two million tonnes in CO2 emissions over the summer.
But the monthly €9 ($9) ticket will no longer be available from Thursday and Chancellor Olaf Scholz's coalition is divided over whether and how it should be replaced.
Greens and Social Democrats want to extend the scheme into the autumn as a winter energy crisis looms, although the price could rise to €49.
But Finance Minister Christian Lindner, the leader of the fiscally cautious Free Democratic Party, said it was not affordable in the long run to subsidise public transport so heavily.
The €9 pass allowed people to board local and regional services anywhere in Germany for a whole calendar month, although long-distance express trains were not covered.
Figures published on Monday by the Association of German Transport Companies (VDV) said 52 million tickets were sold during the three months they were available.
Some passengers said they were driving less because of the ticket, and the atmosphere was spared an estimated 1.8 million tonnes of carbon dioxide over the summer.
The VDV said this was equivalent to a whole year of speed limits on Germany's autobahns, another energy-saving proposal that has divided opinion in Mr Scholz's government.
Customers also praised the flexibility of the ticket, and a German tourism association said it had made holidays in Germany more attractive.
However, the scheme cost the government €2.5 billion and was only planned for three months to help ease the pain of rising fuel costs.
Mr Lindner said the ticket was not affordable beyond the summer and raised eyebrows by suggesting passengers had a “handout mentality”.
The Greens, by contrast, have been lobbying for an extension in which the nationwide ticket would cost €49 from September, while a regional one would be available for €29.
Economy Minister Robert Habeck, the most senior Green in the cabinet, told Deutschlandfunk radio on Tuesday he was optimistic a compromise could be found with colleagues from the FDP.
The government has promised that more help is coming to deal with high prices, but has spent the last week facing criticism over a surcharge it imposed on gas bills.
Ministers said the levy was needed to keep companies paying over the odds to replace Russian gas afloat, and to spread the costs more evenly among consumers.
But Mr Habeck acknowledged he had failed to explain the policy well enough and that changes were needed to stop “free-loading” companies claiming support despite making large profits.
