E-tolling in Gauteng is the only viable way to pay for the R20 billion spent on improving the province's freeways, Deputy Transport Minister Jeremy Cronin said on Wednesday.

"If we could rewind the clock back to 2007, we would not be embarking on this project [Gauteng Freeway Improvement Project] at all. We have made that very clear," he told MPs during debate in Parliament on his department's Budget vote.

"However, alas, there is R20-billion debt. It's been incurred on phase A1 [of the project]. It's about 180 km [of road]."

Cronin, who said any further spending on the project had "categorically" been put on hold, said paying off the project debt by increasing the fuel levy was not an option.

Doing so would be unfair to people living in other parts of the country, who would be paying for infrastructure in Gauteng.

He also ruled out a dedicated Gauteng fuel levy, suggesting it was too onerous and costly to administer.

Cronin was responding to a call made earlier in the House by the Democratic Alliance's Ian Ollis, to implement a small fuel levy to cover the cost of the project.

Ollis told MPs that his party would, if it was in government, immediately cancel the Gauteng e-toll.

"If the DA was in government we would cancel the Gauteng e-toll immediately. In fact we would never have implemented this wasteful collection system in the first place.

"A small fuel levy over time would pay for the highways, as it does on the N6 to Buffalo City, and there are other options."

Ollis described Gauteng's e-toll system, which is set to come into effect at the end of the month, as "the world's most expensive toll collection system".

He said it would cost over R1bn a year just to collect the fees.

"By comparison, a small fuel levy would only cost R4-million per annum to administer and the rest of the money could be put to improving the actual roads," Ollis said.

Cronin agreed that "the particular tolling option that has gone forward is very expensive".

He further said the government appreciated that there was "great unhappiness" over the introduction of e-tolling, and said he empathised with the Congress of South African Trade Unions, which has called on its members to make the tolls unworkable.

Opening the debate on Wednesday, Transport Minister Sibusiso Ndebele said South Africa had a responsibility to service the debt incurred when the project to improve the road network in the province was implemented.

"It is now public knowledge that South Africa has a financial obligation of R20bn to this effect, escalating to R32-billion with interest over the next couple of years.

"Failure to honour this obligation will adversely affect our country's credit rating."

Ndebele said he was "encouraged" by the fact that, to date, a total of 501 245 e-tags had been sold.

The transport department received an overall R39-billion budget allocation for this financial year, which will rise to R48-billion by 2014/15.

About R18-billion of this is earmarked for roads.