The budget allocated $20 million for improvements to the road and intersections between Gungahlin and the city. But the Assembly’s estimates committee, made up of two Labor and two Liberal members, said the government had not made it clear whether that spending was part of the overall project cost.

The amount is just one block of spending, with more going to intersection improvements in Dickson, and more to exploration work to find underground pipes and services.

In addition, $30 million had been budgeted for Capital Metro over two years from July 2013, including $21.3 million this financial year. The amount includes $2.3 million for staff and administration, and $9.8 million for consultancies.

The government has not made it clear what will be included in its overall project cost, which it has put at about $614 million, adjusted from 2011 dollars.

The committee said there was much uncertainty about the assumptions underpinning the light rail project, including population projections, assumptions about the number of people living in the corridor and how far they would be prepared to walk to a station, and projections of more jobs in the corridor.

Plans to link the tram with bus services were still unclear, as was the possibility of a public-private partnership to build and run the line, it said.

The committee pointed to the scale of the money set aside for light rail, and two other projects: $1.3 billion in all for the tram, the new public hospital and the new court building. It called for consultation on the project ''to ensure it is viable, provides value for money and meets the needs of the ACT community''. It also called on the government to table the final cost benefit analysis, the estimated total cost of the project and the delivery model for the project after it had chosen a preferred tenderer but before construction projects were tabled.

The estimates committee delivered a detailed report on Tuesday into the government’s budget, due to be debated and passed next week.

Among 138 recommendations, it called for a further delay to the new payroll tax regime which will force as many as 1000 Canberra contractors, many of whom work for federal government departments, to pay a new 6.85 per cent tax. The government has already delayed the tax until September, but the estimates committee said it should be pushed back further, to July next year, or existing contracts should be ''grandfathered''.

The committee said the change would bring the ACT into line with other states, but it was concerned about the lack of consultation, the lack of time to adjust, and the fact that contracts had already been signed for the 2014-15 year without factoring in the new tax.

The tax would have significant consequences for the viability of some businesses and contractor arrangements, it said.

Among other recommendations, the committee asked for urgent action on emergency housing, Aboriginal housing, housing stress among university students and housing affordability for older women at risk. It heard evidence that homelessness among Aboriginal people in Canberra was the highest of any city in the country. It heard that 1785 Canberrans were homeless, with another 9910 at risk of homelessness, and one in two people seeking emergency accommodation each night were turned away. It heard that on average, Unilodge students paid 52 per cent of their income on accommodation, and share house students in the private market paid close to 81 per cent of their income on accommodation.

The committee called for reports by the government on these housing problems in October and November.

The government will respond to the estimates committee next week. Capital Metro Minister Simon Corbell strongly defended the tram project in the Assembly yesterday.

''What we know is that light rail delivers a long-term carrying capacity that cannot be delivered by a bus network,'' he said. ''It delivers a quality of service and quality of ride that cannot be delivered by bus rapid transit along these corridors. It allows us to integrate public transport into this corridor in a way that bus rapid transit will never be able to deliver along this corridor.''

Mr Corbell said the tram was the ''right long-term investment for our city''.

''It’s a project that is supported by a clear majority of Canberrans and the government will continue to pursue this important city-building project for our city.''