About 17.7 per cent of containers were carried by rail to and from Port Botany last year,down from 19.4 per cent in 2017,figures from the state's transport agency show.
The government and the private owner of the port blamed the drop in rail freight partly on drought crimping agricultural exports,which make up a large share of freight.
Labor's roads spokesman,John Graham,said the figures showed the government would likely miss its target to shift more containers by rail."More trucks on the roads is more accidents,more pollution and more road damage,"he said.
But Transport Minister Andrew Constance cited a planned duplication of a rail line to the port and opening of an intermodal terminal at Moorebank in Sydney's south west as a"game-changer that will see more freight moved by rail across NSW".
While the Moorebank terminal is expected to be commissioned late this year,the $300 millionduplication of a 2.9-kilometre stretch of line from the port to Mascot is not due to be completed until the end of 2023.