Transurban expects the widening of Melbourne's CityLink toll road to be completed in late October, allowing motorists to use the extra lanes three months earlier than planned.

Australia's largest toll road operator said some night work would continue on the widening project until the end of the year but all lanes of CityLink would be open during peak periods by the end of this month.

The $1.3 billion CityLink-Tull widening project includes almost 30 kilometres of new lanes in both directions of the CityLink between Bulla Road and the West Gate Freeway.

Transurban said the project would boost the roadway's capacity by 30 per cent and result in travel time savings of up to 17 minutes for motorists during the busiest periods.