The agency expected the bulk of the roadworks to be completed by the end of the year, it said in a statement.
Lanes made available during the World Cup to allow for free-flowing traffic may need to be closed again to complete these improvements.
"It should, however, be noted that in certain areas the work still needs to be completed, for example, to add the final top layer of the road, to do quality tests and to apply final road markings."
Sanral urged road users to be careful in construction areas and adhere to road signs.
- Sapa