The UK Highways Agency has announced the opening of the first section of a new generation of motorways on the M25.

The eight-mile section in Hertfordshire is the first in the country to feature a new style of smart motorway.

These combine pioneering technology and use of the hard shoulder as a permanent running lane to lower congestion and ease traffic flow.

Smart motorways offer additional road capacity at less cost than traditional road-widening schemes, while remaining at least as safe.

"The additional capacity on the M25 is part of the government’s record investment in the strategic road network."

Roads minister Robert Goodwill said: "The additional capacity on the M25 is part of the government’s record investment in the strategic road network, with £15.1bn being invested to add over 400 lane miles of capacity on our busiest motorways by 2021.

"Our motorways are the backbone of Britain and vital to building the UK economy, with approximately four million vehicles using them each day."

Highways Agency chief executive Graham Dalton said that design changes have meant that smart motorways are quicker to build, more intuitive for drivers and more efficient to operate.

The improvement work was implemented by Connect Plus.

Connect Plus chief executive officer Tim Jones said: "I am delighted that Connect Plus has achieved another major milestone on its journey to transform the M25, on behalf of the Highways Agency, into a high capacity world-class motorway with exemplary levels of safety and reliability.

"We now look forward to operating it in a safe and effective manner and to completing the northern action later this year."

Work to transform the section of motorway between junctions 23 and 25 started in February 2013, and includes infrared CCTV, five super-span gantries over both carriageways, three single-span gantries over one carriageway, nine refuge areas, 20 overhead signals and 28 CCTV cameras.

The second section on the southern part of the M25 is set to open next month, with a third later in the year on the northern section. Similar schemes are also being introduced across the country on the M1, M3 and M62.