South African National Roads Agency Limited (Sanral) needs to be transparent on e-tag sales in light of the impression it was creating that motorists were "clamouring" to be tagged, the Opposition to Urban Tolling Alliance (Outa) said on Monday.

"Sanral's number of 1.2-million e-tags 'taken up' is hogwash," said Outa spokesperson John Clarke in a statement.

"What does 'taken up' mean? If they are inferring that these are fitted in cars making use of the Gauteng freeways, this is misinformation."

On Sunday, Sanral challenged Outa's claim that motorists were not buying e-tags.

Spokesperson Vusi Mona said it was sitting with more than "1.2-million e-tags that have been taken up" and that between 30 000 and 45 000 people were registering each week.

Outa said it was tired of Sanrals' "tit-for-tat" claims.

"For all we know, Sanral's numbers include tags sitting on shop shelves, storerooms and elsewhere, but they are of no use if not fitted to vehicles travelling on the Gauteng freeways," argued Clarke.

"The real question is why does Sanral not allow an independent journalist or auditor to simply take a look at their computer screen, in their operations centre, where this information is readily available?" asked Clarke.

Outa wanted to know the exact percentage of e-tagged vehicles passing under the tolled gantries per day and for the month of February.

The controversial e-tolling system was implemented across Gauteng freeways in December following a long court battle.