Different standards for Sydney's inner west light rail line and a new $2.1 billion line from the central city to the south east mean trams carrying passengers won't be able to switch between the two.

The standards differ on a range of measures including gaps between platforms and carriages, height and width of the actual track, clearances between the track corridor and its surrounds, and distance between the back wheels of the trams.

The lack of "interoperability" between the two lines will limit the ability to introduce new routes across a broader network, such as one from Randwick to Pyrmont.

Trams running on the 12.8-kilometre inner west line, for example, will not be able to carry passengers the entire way from Dulwich Hill to Moore Park for large sporting events. Instead, passengers will have to switch to trams on the new line at Central Station.