Sydney commuters will have to wait at least another two years before new trams are likely to be running on the inner west light rail line to help reduce passenger crowding.

Internal documents obtained by the Herald under freedom of information laws show Transport for NSW intended to "undertake direct negotiations" in about the middle of last year to buy new trams.

But almost a year on, the government agency has yet to strike a deal with French company Alstom or Spain's CAF to purchase four trams, which would increase capacity of the light rail line by up to 1200 passengers an hour during morning and evening peak periods when overcrowding is worst.

Patronage is surging on the inner west light rail line. Credit:Louise Kennerley

The documents detailing potential "short-term enhancements" show that even if a deal is signed, it will take 18 months before all four trams are delivered.