The National Treasury has applied to intervene in the Gauteng e-toll case to be heard by the High Court in Pretoria this week.

"There would be serious negative implications for future financing of roads and investment in public transport, were Sanral to be interdicted from implementing the toll collection system," Treasury said in a statement on Monday.

The Treasury has applied for leave to intervene in the application to be heard by the court on Tuesday.

"National Treasury... will argue that the interdict should be denied and the implementation of toll collection should be permitted to proceed, as has been decided by Cabinet and in keeping with the provisions of the Sanral Act."

The application has been brought by the Opposition to Urban Tolling Alliance, the SA Vehicle Renting and Leasing Association, The Quadpara Association of SA and the SA National Consumer Union.

They want to stop the levying and collection of tolls on certain roads in the Gauteng from going ahead on April 30.

The respondents in the case are the SA National Roads Agency Ltd (Sanral), the Minister of transport, the MEC of roads and transport, Gauteng, the Minister of water and environmental affairs, the director-general of the Department of Water and Environmental affairs, and the National Consumer Commission.

Treasury said the case was important because it affected the state's ability to finance road infrastructure.

It also had significant implications for the integrity and sustainability of the public finances, Treasury said.

"Of concern also is the implication for Sanral's capacity to repay its debt, which is partially guaranteed by government.

"The integrity and sustainability of government's continued access to capital markets is a vital and essential determinant of South Africa's capacity to finance the infrastructure required for economic growth, development and rising living standards," the Treasury said.

Government had contributed R5.75-billion to the project so that user toll fees would be lower, Treasury said.

Tolling of certain major arterial roads was necessary for economic growth and development.

"These routes are those which carry the heaviest traffic load in the country, and serve as critical economic corridors for both freight and personal travel purposes.

"In the case of the Gauteng freeway network, rising traffic volumes and the resulting congestion costs to users are a further argument for the recovery of costs through toll charges."

Treasury said road users benefited through improved safety, lower travel time and lower operating costs.

"Based on the current toll proposals, which exempt taxi operators and other public transport services, higher income users will account for over 95% of toll revenue," Treasury said.