Legislation will be introduced today that will clear the road ahead for semi-trailer lorries after a trial suggested the move will deliver green benefits and reduce transportation costs.

But critics are warning the move isn't as green as the Department for Transport claims – and could spell "alarming" risks for pedestrians and other road users.

Transport operators will be able to run combinations up to 18.55 metres (61 feet), which represents a 2.05 metre increase on existing rules.

Richard Holden, Roads Minister, said: "Everyone around the country depends on our haulage sector for their everyday needs - from loo rolls to sausage rolls – and a strong, resilient supply chain is key to the government's priority to grow the economy.

"These new longer lorries will make a big difference for British businesses like Greggs, who will see 15% more baked goods delivered, from tasty pastries to the nation's much-loved sausage rolls.

"It's fantastic to see this change for our supply chain come into law, resulting in a near £1.4bn boost to the haulage industry and driving economic growth. Let the good times roll as we reduce congestion, lower emissions and enhance the safety of British roads."

The haulage industry reckons the load capacity boost per journey will translate into 8% fewer journeys (removing one lorry per 12 trips) and the government says an 11-year trial proved semi-trailers were 61% less likely to feature in personal injury collisions than conventional lorries.

Gavin Kirk, supply chain director at Greggs, said: "We were early adopters of the trial as we saw a significant efficiency benefits from the additional 15% capacity that they afforded us.

"Our drivers undertook additional training to use these trailers and we have monitored accidents, finding that they are as safe as our standard fleet. Due to the increased capacity, we have reduced our annual km travelled by 540,000, and saved 410 tonnes of carbon per year from LSTs, which supports our wider ESG agenda, The Greggs Pledge."

Greggs has been running semi-trailers from its Newcastle distribution centre since 2013 and converted 20% of its trailer fleet as part of the trial. The food giant believes the law change will allow a 15% boost on its delivery cost margins.

Mr Holden added that the move was part of the government's strategy to grow the economy though a "strong, resilient supply chain".

He said: "That's why we're introducing longer semi-trailers to carry more goods in fewer journeys and ensure our shops, supermarkets and hospitals are always well stocked," he said.

While length increases, maximum haulage weight will remain at 44 tonnes and operators will be required to instigate appropriate route plans and risk assessments, as well as implementing extra safety checks, driver training, record keeping and training for transport managers and key staff.

Other brands to take up the trial using 3,000 semi-trailers have included Morrisons, Stobart, Royal Mail and Argos with environmental benefits cited as a reduction of 70,000 tonnes of CO2 and 97 tonnes of NOx over the trial, the latter saving equivalent, said the Department for Transport, to the entire annual NOx emissions of around 2,000 diesel cars per year.

But the Daily Mail claimed that the new lorries would take up a fifth of any layby refuge area on smart motorway sections in the UK while safety watchdogs RoSPA, in a response to the trial, have stated: "RoSPA agrees that LSTs should be permitted with no restriction on LST numbers, although with additional regulations to those imposed on HGVs."

And cyclists are unlikely to welcome the change.

Keir Gallagher, campaigns manager at Cycling UK, said: "At a time when funding for infrastructure to keep people cycling and walking safer has been cut, it's alarming that longer and more hazardous lorries could now be allowed to share the road with people cycling and walking."

Citing green concerns, the Campaign for Better Transport has slammed the move as damaging to track alternatives.

Norman Baker, spokesman, said: "This is a deeply retrograde step which will do nothing to tackle carbon emissions or air pollution and will disadvantage parallel rail freight routes.

"These lorries are by nature more dangerous than current HGVs, so the last thing people want is them thundering through their communities. Rather than longer, heavier lorries the Government should be investing in rail freight as a safer, cleaner and more efficient alternative."

The RAC has also warned of the danger of semi-trailers on diverted, unplanned routes.

Steve Gooding, RAC Foundation director said: "Particular attention will need to be paid to diversion routes when motorways and major A roads are closed for repair, as they often are."