Today's official data release from the government confirmed what many already suspected - transport is the laggard in the UK's shift to a greener economy.

In 2017 emissions from road, rail, shipping and domestic air travel made up 27 per cent of total greenhouse gas emissions, registering no improvement on 2016 rates, and remaining the single largest pollution source for the UK. Clearly, for all the talk of electric cars, green taxis and hydrogen trucks, the UK is failing to move fast enough on transport emissions. The brutal truth is that since 1990, we have only managed to cut transport emissions by two per cent.

The reasons for this are manifold, but the short answer is that it's down to emissions from petrol and diesel cars on the road. Almost 90 per cent of all trips in the UK are conducted by road, a figure which has remained almost static for the last 10 years. Journeys on public bus services represent a falling percentage of this: since 2011 the number of journeys taken by local bus in the UK has fallen by 340 million according to Department for Transport data. Travel on the rail network has been steadily rising despite unpopular fare increases, but is sharply concentrated in the commuter belt around London's South East. For most of the rest of the country, the dominant mode of transport is the private car.

Green transport campaigners insist the way to finally start making progress on transport emissions is to encourage people out of their private cars and back onto public transport. A new report released today by the Campaign for Better Transport (CBT) is calling for a massive expansion in the UK's rail network to connect 500,000 people living in disadvantaged communities with rail travel.

The move would require a £4.8bn investment from government to build out 33 new rail lines and 72 new stations, but would deliver an extra 20 million rail passenger journeys a year, CBT claimed, and a correspondingly sizeable cut to road miles.

The report claims such an investment would bring valuable social benefits, such as supporting low-carbon housing developments where car ownership would not be essential - unlike many new developments today. Meanwhile better air quality, more options for sustainable freight transport, and lower carbon emissions are just some of the environmental benefits on offer.

"Expanding the railways would transform the opportunities for people living in some of the most deprived areas of the country, giving them greater access to employment and services and providing a much needed boost to local economies," argued CBT chief executive Darren Shirley.  

It's a point the International Energy Agency (IEA) agrees on. Earlier this month it released a bumper report extolling the "substantial benefits" of rail as a means of lowering transport energy use, cutting emissions and boosting air quality.  

But if we are to really push the world into embracing rail travel, investment in new infrastructure needs to rapidly ramp up. According to the IEA's base case scenario, which assumes no significant new emphasis on rail in global policymaking, rail travel only manages to maintain its current share of activity relative to cars through to 2050.

To ensure rail travel takes on more of the transport load, the IEA says significant new policies are needed to minimise the cost of rail travel for consumers and ensure other transport modes pay for their external social and environmental impacts, through carbon taxes or congestion charges.

Interestingly, under the IEA's 'High Rail' scenario - where such policies are modelled - other public transport activities also increase, particularly bus travel. This is in large part due to the development of transport systems that allow for better integration of rail services with other public transport options, the IEA says.

That will be music to the ears of green groups calling for more support for local bus services in the UK, which they argue are also key to cutting private car use, particularly in rural areas of the country. Research out today by transport consultancy Transport for Quality of Life, commissioned by Friends of the Earth, suggests radical action is needed over and above the government's existing Road to Zero strategy if the UK is to meet its Paris Agreement targets. Car travel will need to drop by 20-60 per cent between now and 2030, the paper estimates, to stay within transport's carbon budget for a 1.5C scenario.

Although increased rail travel will play a part in this, the bus network will also have to up its game. Britain should look to Europe for guidance on this, the paper argues, particularly in Munich, where investment in a "one network, one timetable, one ticket" system has cut car use and boosted numbers using public transport.

Thanks to new powers awarded to local mayors, such a system is now possible in parts of the UK, the paper suggests. Mayors can bring in new regulations for bus services, demanding routes are designed to seamlessly integrate with other services and transport modes, including rail. New green bus technologies, including hydrogen and electric power, should also be mandated to deliver cuts to greenhouse gases and air pollution measures.

These efforts, combined with consumer-friendly policies such as free bus travel, would help make public transport a much more appealing option, the researchers argue. "Our research makes it clear that UK transport policy requires a complete overhaul to enable us to comply with greenhouse gas reduction needs and other pressing public health concerns such as air quality and obesity," said Lynn Sloman, the director of the Transport for Quality of Life.

The government, for its part, insists it is committed to driving down transport emissions, with its Road to Zero strategy targeting all new cars and vans to be zero emission by 2040. "We also support bus travel through £250m every year, as well as a further £1bn for the free bus pass scheme, paving the way to a more sustainable future," a spokeswoman pointed out. Officials are also examining proposals to re-open rail routes, the department added. 

Switching to zero emission vehicles will make a dent in the UK's transport emissions, but today's research suggests that this alone will not be enough to deliver on our climate commitments. Perhaps it's time to park the cars, and see how far down the low-carbon road the UK can travel on buses and trains instead.