Growing congestion along Canberra's planned light rail route is already costing the city's drivers more than 35,000 lost minutes every day, according to the project's final business case.
Despite Canberra's reputation as a city free of the peak-hour gridlock faced by drivers in Sydney and Melbourne, the document released on Friday estimates drivers along the 12-kilometre route lose the most time per vehicle travelling south between Exhibition Park and the city.
About 3000 car trips are made on the stretch of road between Gungahlin and EPIC to get to work, losing almost10,000 minutes a day because of road congestion.
A further 25,000 minutes are lost to commuters during the 5000 car journeys from EPIC to the city.
Car trips from Civic to Russell lose about 5000 minutes a day, and Russell to Civic loses about 3000 minutes, according to the business case released by Chief Minister Katy Gallagher and Capital Metro Minister Simon Corbell.
Population growth and road congestion have been central to the government's long-running case for the construction of light rail, and the business case forecasts Gungahlin growing by 20,000 residents by 2021.
With that population increase, driving time to the city would increase to 57 minutes by 2031 without a tram line being built. Trams along Northbourne Avenue, the Federal Highway and Flemington Road would have the average car journey fall to 42 minutes at peak.
About 13,400 Canberrans live and work along the tram line corridor and more than 70 per cent travel to work between Macarthur Avenue and the city.
The business case estimates congestion has led to travel times of 35 to 45 minutes in the morning peak from Gungahlin to the city.
Passengers on the new service will reach the city in 25 minutes.
The savings could be up to $222 million from costs associated with traffic congestion during 30 years, as well as up to $5 million in positive health outcomes.
According to the document, which is being considered by potential private partners for the project, the northside suburbs of Bonner, Casey, Harrison and Crace experienced the city's biggest population growth in the decade to 2011.
Gungahlin's population is expected to grow from about 50,000 to 84,800 in 2031.
The document also describes Northbourne Avenue as a "sub-optimal" gateway to Canberra as the national capital, labelling some parts of its development since World War II as "visually unappealing [and] adversely impacting first impressions of the city".
Forecasting growth for an extra 45,000 residents along the tram route, the business case says visitors and occupants could form "a generally undesirable impression of the city" because of the area's appearance.
Poor impressions may also "contribute to lower property value growth along Northbourne Avenue", it says.
Australasian Railway Association chief executive Bryan Nye welcomed the release of the business case showing the tram's benefits outweighed the costs for Canberra by a ratio of 1:2.
"Light rail is proven to improve the socio-economic and environmental performance of a city, by reducing road congestion; decreasing travel times on roads; improving road safety; emitting less greenhouse gas emissions; and promoting healthier, more-active lifestyles," Mr Nye said.
"Public transport commuters are five times more active than those who drive to work, and with Canberra being one of Australia's most car-dependent cities with only 7.9 per cent of people commuting to work by public transport, the nation's capital needs this project more than ever."
He said trams could reinvigorate public transport in Canberra with successful integration into the existing ACTION bus network.