This is the third and final policy blog in the series investigating train length. The purpose is to survey the impacts and implications of longer trains to the U.S. economy, public safety, and the world. Because railroads are so central to the nation’s supply chain and transportation network, it is essential that the public and policymakers know and weigh the costs and benefits of train activity. With the recent attention on longer trains, it is important to lay out a framework for evaluation.

While this series does not attempt to settle the issue once and for all, we provide useful lenses to view longer trains and raise key data and theory for lawmakers before changing public policy. In this blog, the climate impact of longer trains is the central focus. That will necessarily include a discussion of trains themselves and related industries.

To evaluate the climate impact of train length, we look at fuel consumption and carbon emissions, hazardous material incidents, and externalities the public experiences.


Climate Impact


Fuel and Emissions

Trains are one of the most fuel efficient ways to move freight and cargo, and over land are unmatched for moving these loads long distances. By nature, linking train cars allows more payload to be attached to the same locomotive with minimal reduction in fuel efficiency. It requires less fuel to add marginal train cars to the consist than to add those same additional cars to a separate, second train. According to the Association of American Railroads, limiting train length to 7,500 feet, for instance, would result in an approximate 13 percent increase in fuel consumption annually. That would require railroads to utilize over 420 million more gallons of fuel than present levels. This has a direct impact of emissions coming from the diesel-powered locomotives.

Another alternative to running multiple trains is to divert freight to trucking. On average, a freight train can move a ton of freight nearly 500 miles on a single gallon of diesel, while the average truck moves this same ton just over 100 miles on one gallon of diesel. On top of trucks having only a quarter of the fuel efficiency, a train car can carry more than twice the freight load of trucks. For example, 100 rail cars of intermodal cargo moving from Charleston, SC to Washington, D.C. is the equivalent to 245 trucks. That load moving by train rather than truck prevents over 160 tons of carbon dioxide emissions.

Hazardous Material

When it comes to the environment, the most common concern people have is the potential for derailments and release of hazardous material. To establish context, trains have grown in length over the last two decades and the number of derailments has declined over the same period. This is not intended to establish a causal correlation between longer trains and lower derailments, but to provide evidence that it seems unlikely train length contributes to derailment risks. The advent of positive train control (PTC) technology and related innovative solutions has been linked to improved rail safety. The use of PTC and related technology can be expected to maintain rail safety even on longer trains.

Along with a reduced risk and a historic low number of derailments, the release of hazardous material by train is very rare. In fact, over the last 22 years, less than one percent (0.87 percent) of reported incidents identified a release of hazardous materials. With train length increasing over this interval and derailments declining, there is insufficient data to suggest that train length is associated with any risk of hazardous material release.

This low number is also validated by the overall 99.99 percent effectiveness rate for moving hazardous material by rail to its destination without incident:

Hazardous products transported by rail tanker car arrive at the destination over 99.99 percent of the time without a release caused by a train accident. The leak, spill, or accident rate below 0.01 percent makes rail the second safest in-land transportation method with rail spilling the least volume of hazardous material of any in-land method. Overall, in comparison to other forms of transportation, oil is spilled from railroad transports more frequently than pipelines, however rail loses significantly less oil from accidents in comparison to pipelines, given the larger volumes moved by pipe. Rail effectively transports between 100 million and 200 million barrels of crude and petroleum products each year.

In line with analysis around safety and costs, it is important to assess the impact of running multiple trains and diversion of hazardous material onto trucks. While the risk of derailment is statistically small on a modern freight train, the risk is theoretically increased by running two trains with hazardous material loads relative to running a single longer train. Similarly, trucks move hazardous materials safely over 99 percent of the time, but move on much more dynamic and unpredictable roadways relative to track-bound rail infrastructure. The risk of a roadway accident is much higher than a rail accident, making the marginal shift from train to truck for hazardous materials a greater risk to the environment.

In a future report, we will plot longer trains against hazardous material releases to further understand this relationship. Finally, it is true that regardless of the contributing cause (i.e. even if train length does not cause the accident), for derailments that do occur, the longer the train, the more train cars and tankers there are that may derail or release hazardous materials. If a long train derails because of a human error or equipment malfunction that can definitively be separated from the length, the great number of cars may still generate environmental risk.

Similarly, there is a marginal impact of train length on other accident types simply by prolonging the stopping time of a train. Longer trains are heavier and have more momentum than shorter trains (depending in part on the cargo and consist) meaning that potential issues like overheated wheel bearings may be more difficult to slow and stop to address. In that event, the precise relationship between train length and any resulting derailment and release of hazardous material must be rigorously and precisely investigated. Law and regulation should not be made on broad assumptions.


The costs and impacts that are created by longer trains but not fully internalized by the rail industry include certain environmental impacts. With blocked crossings being the primary consideration for long trains, the main externality is traffic and idling of road vehicles. These contribute to emissions, as vehicles burn fuel and stay on the road longer than they would if no crossing was blocked. The overall impact of this is unknown, as the federal government is still collecting data on blocked crossings. If the data demonstrates that there is a statistically significant increase in blocked crossings that is causally connected to train length, it must still be evaluated in net terms against the emissions avoided or prevented by using a longer train. The data is not available at this time.

A final externality is once again a possible consequence of long trains that is not necessarily causally related. If a train derails for whatever reason, the greater number of cars may also require more emergency vehicles to respond to, lead to more emissions or releases of hazardous materials, and impact communities for weeks as clean up and remediation is undertaken. These risks can be mitigated through improved inspections and maintenance along with technology.

More research by the federal government is underway. With this brief series providing some considerations and frameworks for analysis, we conclude that train length is not fully understood and while it may impose costs also has clear benefits. Regulators and lawmakers must understand and balance these costs and benefits before altering the rules and regulations of this critical component of the supply chain. Regulating based on costs without appropriately factoring in the benefits will create its own negative externalities.

To stay up to date, read the first two blogs covering safety and costs.


Written by Benjamin Dierker, Executive Director


The Alliance for Innovation and Infrastructure (Aii) is an independent, national research and educational organization. An innovative think tank, Aii explores the intersection of economics, law, and public policy in the areas of climate, damage prevention, energy, infrastructure, innovation, technology, and transportation.