If an interdict preventing e-tolling in Gauteng was granted, it could be in effect for the rest of the year, the High Court in Pretoria heard on Thursday.
"If the interdict is granted, in all legal reality, it must stand until the end of litigation, which would not be set to end any time soon... maybe until the end of the year," Treasury lawyer Jeremy Gauntlett said.
This was due to the time required for the review, as well as further court hearings and appeals.
He said if the SA National Roads Agency Ltd (Sanral) defaulted on one month of its payment, the government would have to pay its entire debt.
"It does not mean that government would not be able to meet it [the debt], it has to, but at what cost? For this country to sustain R20 billion in unbudgeted capital is a serious matter," Gauntlett said.
He said the government would have to neglect other social and economic obligations to pay off the debt.
"The milk has been spilt with regards to the roads, and people are using them. The issue now is how to pay for them. It has to be paid for. You can say you don't like it, but you can't say that it is irrational."
He said the previous four delays to the e-toll system had come at a "great cost".