The climate impact of transport is surprisingly complicated

Emissions in action. Image: Getty.

The 2020s will have to involve some very big decisions about transport – the UK’s most polluting sector. The UK government’s response so far has been erratic, choosing to intervene to prevent the collapse of Flybe (Europe’s biggest regional airline) and give the green light for the high-speed rail project, HS2.

Decarbonising transport would eliminate 26 per cent of UK CO₂ emissions that come from how people get around. But Prime Minister Boris Johnson recently said that doing this poses “difficult and complicated” questions. On this, Johnson is almost certainly right.

The gilets jaunes protests against fuel duty rises in France show the delicate balancing act between decisive climate action and continued economic growth and convenience. But shouldn’t the government allow a regional flight operator to fail and invest in high-speed rail instead? The answer is not so simple.

Carbon footprints can be misleading

Aviation is one of the fastest growing fossil fuel consumers, with airlines contributing about 3.5 per cent of all man-made greenhouse gas emissions. This might seem small, but a single transatlantic flight from London to New York can grow your personal carbon footprint by as much as the entire heating budget of the average European.

At high altitudes, contrails – the white lines we see in the sky – are formed in the wake of aircraft. These high altitude clouds are too thin to reflect much sunlight, but the ice crystals inside them can trap heat. Unlike low-level cloud, which has a net-cooling effect, contrails contribute significantly to global warming, effectively boosting the aviation industry’s share of greenhouse gas emissions to around 4.9 per cent.

For the most part, the environmental benefit of high-speed rail is taken for granted. Most, but not all, research suggests that high-speed rail can offset emissions from aviation if it can attract enough passengers from alternative air routes. But the relative climate impacts of aviation to other modes of transport depend on more than just engines and altitude.

We can compare the emissions of different forms of transport by calculating the emissions produced by each one when moving one passenger one kilometre. This effectively compares how much CO₂ leaves each vehicle’s exhaust, but it ignores greenhouse gas emissions from the building and maintenance of the vehicles, the infrastructure – such as tracks, runways and airports – and the production of fuel.

The warming effects of different greenhouse gases happen over different time periods, from a few days of short intensive warming to centuries of gentle influence. In order to provide a common unit to measure the impact of different gases, warming effects are standardised over a given time period. The time period normally used is 100 years.


But if it were five years, the effect of contrails would account for more global warming than all the cars in the world. They raise the temperature of the atmosphere in short, intense bursts. On longer timescales, like 20 years, the short term effects are less important and make aviation look considerably better – with flying looking potentially less damaging than some cars over the same distance.

This is still not the whole story though. The energy inputs for different modes of travel vary. The direct burning of fossil fuels in engines, for example jet kerosene in aircraft, emits greenhouse gases. In electrically powered high-speed rail, operating the train produces no emissions, except from the fossil fuels used to generate that electricity elsewhere.

Developing HS2 will mean deploying stations, tracks and centres of communication, and they’ll need ongoing maintenance. These all need energy and material investments, which will create further greenhouse gas emissions through manufacture, transport, and use. That could increase the carbon footprint of rail by between 1.8 and 2.5 times, over just accounting for the operation of the trains. For aviation, the same infrastructure requirements are relatively small, and are responsible for a 1.2–1.3 increase, with road transport showing a 1.4–1.6 increase.

Comparing life cycles

A life cycle approach gives a better understanding of where emissions are occurring and compares transport modes on a much more level playing field. This helps us understand that most greenhouse gas emissions in air and road travel come from flying and driving, whereas in rail travel, the climate effects are dominated by those emissions produced building the infrastructure itself. Emissions from operating trains are generally lower because of the heavy reliance on electricity. But there are still emissions from the manufacture and maintenance of renewable energy technologies to consider.

All modes of high-speed travel come with a cost to the environment. Being able to accurately compare the energy requirements and emissions of different transport options is the first step towards addressing their climate impact.

Governments often try to encourage people to change their behaviour and reduce the number of flights they take. But in the case of HS2, the continued availability of regional flights means that only 4 per cent of drivers and only 1 per cent of aeroplane passengers are likely to change their behaviour.

It’s easy to point the finger at aviation and view rail as a low carbon alternative. But governments need to consider and carefully balance the true climate impacts of a transport project, in every phase of its development.

The Conversation

Laurie Wright, Senior Lecturer, Warsash School of Maritime Science and Engineering, Solent University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

To build its emerging “megaregions”, the USA should turn to trains

Under construction: high speed rail in California. Image: Getty.

An extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, out now from Island Press.

A regional transportation system does not become balanced until all its parts are operating effectively. Highways, arterial streets, and local streets are essential, and every megaregion has them, although there is often a big backlog of needed repairs, especially for bridges. Airports for long-distance travel are also recognized as essential, and there are major airports in all the evolving megaregions. Both highways and airports are overloaded at peak periods in the megaregions because of gaps in the rest of the transportation system. Predictions for 2040, when the megaregions will be far more developed than they are today, show that there will be much worse traffic congestion and more airport delays.

What is needed to create a better balance? Passenger rail service that is fast enough to be competitive with driving and with some short airplane trips, commuter rail to major employment centers to take some travelers off highways, and improved local transit systems, especially those that make use of exclusive transit rights-of-way, again to reduce the number of cars on highways and arterial roads. Bicycle paths, sidewalks, and pedestrian paths are also important for reducing car trips in neighborhoods and business centers.

Implementing “fast enough” passenger rail

Long-distance Amtrak trains and commuter rail on conventional, unelectrified tracks are powered by diesel locomotives that can attain a maximum permitted speed of 79 miles per hour, which works out to average operating speeds of 30 to 50 miles per hour. At these speeds, trains are not competitive with driving or even short airline flights.

Trains that can attain 110 miles per hour and can operate at average speeds of 70 miles per hour are fast enough to help balance transportation in megaregions. A trip that takes two to three hours by rail can be competitive with a one-hour flight because of the need to allow an hour and a half or more to get to the boarding area through security, plus the time needed to pick up checked baggage. A two-to-three-hour train trip can be competitive with driving when the distance between destinations is more than two hundred miles – particularly for business travelers who want to sit and work on the train. Of course, the trains also have to be frequent enough, and the traveler’s destination needs to be easily reachable from a train station.

An important factor in reaching higher railway speeds is the recent federal law requiring all trains to have a positive train control safety system, where automated devices manage train separation to avoid collisions, as well as to prevent excessive speeds and deal with track repairs and other temporary situations. What are called high-speed trains in the United States, averaging 70 miles per hour, need gate controls at grade crossings, upgraded tracks, and trains with tilt technology – as on the Acela trains – to permit faster speeds around curves. The Virgin Trains in Florida have diesel-electric locomotives with an electrical generator on board that drives the train but is powered by a diesel engine. 

The faster the train needs to operate, the larger, and heavier, these diesel-electric locomotives have to be, setting an effective speed limit on this technology. The faster speeds possible on the portion of Amtrak’s Acela service north of New Haven, Connecticut, came after the entire line was electrified, as engines that get their power from lines along the track can be smaller and much lighter, and thus go faster. Catenary or third-rail electric trains, like Amtrak’s Acela, can attain speeds of 150 miles per hour, but only a few portions of the tracks now permit this, and average operating speeds are much lower.

Possible alternatives to fast enough trains

True electric high-speed rail can attain maximum operating speeds of 150 to 220 miles per hour, with average operating speeds from 120 to 200 miles per hour. These trains need their own grade-separated track structure, which means new alignments, which are expensive to build. In some places the property-acquisition problem may make a new alignment impossible, unless tunnels are used. True high speeds may be attained by the proposed Texas Central train from Dallas to Houston, and on some portions of the California High-Speed Rail line, should it ever be completed. All of the California line is to be electrified, but some sections will be conventional tracks so that average operating speeds will be lower.


Maglev technology is sometimes mentioned as the ultimate solution to attaining high-speed rail travel. A maglev train travels just above a guideway using magnetic levitation and is propelled by electromagnetic energy. There is an operating maglev train connecting the center of Shanghai to its Pudong International Airport. It can reach a top speed of 267 miles per hour, although its average speed is much lower, as the distance is short and most of the trip is spent getting up to speed or decelerating. The Chinese government has not, so far, used this technology in any other application while building a national system of long-distance, high-speed electric trains. However, there has been a recent announcement of a proposed Chinese maglev train that can attain speeds of 375 miles per hour.

The Hyperloop is a proposed technology that would, in theory, permit passenger trains to travel through large tubes from which all air has been evacuated, and would be even faster than today’s highest-speed trains. Elon Musk has formed a company to develop this virtually frictionless mode of travel, which would have speeds to make it competitive with medium- and even long-distance airplane travel. However, the Hyperloop technology is not yet ready to be applied to real travel situations, and the infrastructure to support it, whether an elevated system or a tunnel, will have all the problems of building conventional high-speed rail on separate guideways, and will also be even more expensive, as a tube has to be constructed as well as the train.

Megaregions need fast enough trains now

Even if new technology someday creates long-distance passenger trains with travel times competitive with airplanes, passenger traffic will still benefit from upgrading rail service to fast-enough trains for many of the trips within a megaregion, now and in the future. States already have the responsibility of financing passenger trains in megaregion rail corridors. Section 209 of the federal Passenger Rail Investment and Improvement Act of 2008 requires states to pay 85 percent of operating costs for all Amtrak routes of less than 750 miles (the legislation exempts the Northeast Corridor) as well as capital maintenance costs of the Amtrak equipment they use, plus support costs for such programs as safety and marketing. 

California’s Caltrans and Capitol Corridor Joint Powers Authority, Connecticut, Indiana, Illinois, Maine’s Northern New England Passenger Rail Authority, Massachusetts, Michigan, Missouri, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Texas, Vermont, Virginia, Washington, and Wisconsin all have agreements with Amtrak to operate their state corridor services. Amtrak has agreements with the freight railroads that own the tracks, and by law, its operations have priority over freight trains.

At present it appears that upgrading these corridor services to fast-enough trains will also be primarily the responsibility of the states, although they may be able to receive federal grants and loans. The track improvements being financed by the State of Michigan are an example of the way a state can take control over rail service. These tracks will eventually be part of 110-mile-per-hour service between Chicago and Detroit, with commitments from not just Michigan but also Illinois and Indiana. Fast-enough service between Chicago and Detroit could become a major organizer in an evolving megaregion, with stops at key cities along the way, including Kalamazoo, Battle Creek, and Ann Arbor. 

Cooperation among states for faster train service requires formal agreements, in this case, the Midwest Interstate Passenger Rail Compact. The participants are Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin. There is also an advocacy organization to support the objectives of the compact, the Midwest Interstate Passenger Rail Commission.

States could, in future, reach operating agreements with a private company such as Virgin Trains USA, but the private company would have to negotiate its own agreement with the freight railroads, and also negotiate its own dispatching priorities. Virgin Trains says in its prospectus that it can finance track improvements itself. If the Virgin Trains service in Florida proves to be profitable, it could lead to other private investments in fast-enough trains.

Jonathan Barnett is an emeritus Professor of Practice in City and Regional Planning, and former director of the Urban Design Program, at the University of Pennsylvania. 

This is an extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, published now by Island Press. You can find out more here.