The Greens say they would make every second service during peak times on the Woden to City line express. Services typically run every five minutes in the busiest periods.

Greens candidate for Murrumbidgee Emma Davidson said it could cut 10 minutes off the estimated 25-30 minute travel time on the route.

But Transport Minister Chris Steel has dismissed the idea, saying it would simply cause a traffic jam of light rail vehicles.

"It is impossible to have an express light rail service," he said.

"This is a very poorly thought out announcement from the Greens and shows they can't be trusted to deliver an effective light rail system for Canberra.

"Can the Greens show any example in the world of an express light rail service working in peak?

"As with the successful first stage - light rail to Woden will run every five minutes or less, so you'd need to build twice as much track if you want to deliver 'express' services - where will the track go? It literally won't fit.

"Even if you only added 'overtaking lanes' the light rail network still interacts with the road network - what happens then?"

He said it would also be impossible to build an overtaking lane between State Circle and the city.

"So do light rail vehicles just bunch up?" Mr Steel said.

Ms Davidson said the Greens had received expert advice that the plan was feasible without extra tracks.

"It would be about timetabling, an express service would leave and then one minute later a service stopping all stations," she said.

The expert advice was not immediately provided.

"If they're going to build a light rail service from City to Woden we want to make sure it's a service that people will actually use," Ms Davidson said.

"If we can make it the fastest transport option then it will actually get used."

She said the government should also be planning to create bypass and crossing infrastructure at some of the stations for when future, more complex services were required.

Public Transport Association of Canberra chair Ryan Hemsley said the Greens' plan did not appear to be feasible.

He said the focus should instead be on making sure the total travel time for the route - stopping all stations - was as fast as possible.

There was no technical reason the travel time couldn't be closer to 20 minutes," Mr Hemsley said.

"Internationally and domestically with the development of new services ... the trend is providing all stop services as opposed to express," he said.

On Monday afternoon, Ms Davidson conceded the plan could not be achieved through timetabling alone and would require additional infrastructure.

She maintained bypass lanes at stops should be built to allow express light rail vehicles to overtake ones stopping all stations.