Gauteng motorists should know by October exactly how much they would pay a kilometre to travel on Gauteng's new and improved freeways, said South African National Roads Agency Limited (Sanral) Gauteng Freeway Improvement Project (GFIP) project leader Alex van Niekerk on Thursday.

The estimates bandied about since 2007 varied between 50 c/km, to the more recent 65 c/km. The tolling model included a discount for frequent users.

"The Minister of Transport has to approve the toll structure," said Van Niekerk.

Construction on the first of the overhead toll gantries of the open-road tolling system - no stopping required - had already started, with one such gantry nearing completion near the John Vorster off-ramp, in Centurion.

Tolling on the 185 km of road which made up the first part of the GFIP would start in April, next year, and would make use of 42 gantries.

"Motorists can start registering for using the system in January," noted Van Niekerk.

Motorists using Gauteng freeways would, for example, be required to buy an electronic toll tag off the shelf at a major retail chain or at a dedicated kiosk. They must then register this tag, by phoning a call centre or going on-line, and load money onto this tag before they enter the road system.

Van Niekerk said that Sanral did expect an increase in traffic volumes on secondary roads once tolling was implemented, but added that this situation was not expected to persist.

"Yes, there will be an initial diversion, but then people will realise the benefit of not sitting in traffic, and they will return to the system."

The GFIP would see vehicles being tolled not according to the number of axles, as was the norm, but on vehicle volume, which would be determined by equipment on the overhead gantries.

Van Niekerk said that the roll-out of the first phase of the GFIP was likely to be followed up by the implementation of urban tolling in some parts of Cape Town, and also Durban and Pietermaritzburg.

The first phase of the GFIP was to be followed by more phases, which would see the construction of new freeways as it progressed.