This is a video from a civil engineer talking about some of the factors affecting the energy efficiency of railcars and the way railways try to design their tracks to minimize resistance. The...
This is a video from a civil engineer talking about some of the factors affecting the energy efficiency of railcars and the way railways try to design their tracks to minimize resistance.
The paper he mentions near the beginning is "Resistance of a Freight Train to Forward Motion" (1977) by John D. Muhlenberg. The equation he talks about for a set of traincars (the modified Davis formula) is:
R = 0.6*(20/w) + (0.01*V) + (0.07*v^2 / w*n)
Where R is resistance in lbs per ton of car weight, V is velocity in mph, w is weight in tons per axle, and n is the number of axles per car. There are more formulas described in that paper, and I bet there are more modern ones too, but I haven't looked. The formula demonstrates the extremely low resistance of traincars relative to rubber-on-asphalt equivalents. Intuitively, this makes sense: think about how long it takes a train to brake!
The takeaway is that from an energy, fuel efficiency, and resistance standpoint, the most efficient way to transport freight (especially over long distances) is by rail. This means that it is cheaper to transport a good by rail over a given distance than by, say, truck or plane. It also significantly reduces environmental emissions: modern electric trains are ridiculously efficient, and even modern diesel trains have very low emissions per ton of cargo transported (possibly less in lifecycle terms than their equivalent by electric truck (!), but I haven't done this calculation and it would depend on a bunch of factors). However, many markets make use of this efficient option poorly, choosing less efficient transportation options that experience more resistance. For example, the United States ships about 40% of long-distance goods by rail, but the share in Europe is significantly lower. (Some readers may find this ironic.)
Technically, the utility of trucking or other road-based freight transport (such as small electric delivery trucks and large cargo bikes) is to transport goods into regions that railways cannot necessarily economically access, such as extremely mountainous geographies and some "last-mile" journeys to destinations that would be impractical to build a railway to. As the narrator notes, railway grade is a limiting factor in its effectiveness – more so than for trucks. In practice, one of the reasons it is more common than is theoretically/mathematically optimal is because governmental incentives and recurring funding mechanisms to construct and maintain road-based freight infrastructure in a country like the United States are high relative to those for rail-based freight infrastructure.
Railfans commonly deride freight rail companies for delaying passenger trains, which is indeed a problem, but it's also worth remembering that they're essential to achieving net-zero emissions targets. A truly environmentally sustainable freight transportation industry is not one that relies exclusively or even mostly on electric trucks.
This is a video from a civil engineer talking about some of the factors affecting the energy efficiency of railcars and the way railways try to design their tracks to minimize resistance.
The paper he mentions near the beginning is "Resistance of a Freight Train to Forward Motion" (1977) by John D. Muhlenberg. The equation he talks about for a set of traincars (the modified Davis formula) is:
R = 0.6*(20/w) + (0.01*V) + (0.07*v^2 / w*n)Where
Ris resistance in lbs per ton of car weight,Vis velocity in mph,wis weight in tons per axle, andnis the number of axles per car. There are more formulas described in that paper, and I bet there are more modern ones too, but I haven't looked. The formula demonstrates the extremely low resistance of traincars relative to rubber-on-asphalt equivalents. Intuitively, this makes sense: think about how long it takes a train to brake!The takeaway is that from an energy, fuel efficiency, and resistance standpoint, the most efficient way to transport freight (especially over long distances) is by rail. This means that it is cheaper to transport a good by rail over a given distance than by, say, truck or plane. It also significantly reduces environmental emissions: modern electric trains are ridiculously efficient, and even modern diesel trains have very low emissions per ton of cargo transported (possibly less in lifecycle terms than their equivalent by electric truck (!), but I haven't done this calculation and it would depend on a bunch of factors). However, many markets make use of this efficient option poorly, choosing less efficient transportation options that experience more resistance. For example, the United States ships about 40% of long-distance goods by rail, but the share in Europe is significantly lower. (Some readers may find this ironic.)
Technically, the utility of trucking or other road-based freight transport (such as small electric delivery trucks and large cargo bikes) is to transport goods into regions that railways cannot necessarily economically access, such as extremely mountainous geographies and some "last-mile" journeys to destinations that would be impractical to build a railway to. As the narrator notes, railway grade is a limiting factor in its effectiveness – more so than for trucks. In practice, one of the reasons it is more common than is theoretically/mathematically optimal is because governmental incentives and recurring funding mechanisms to construct and maintain road-based freight infrastructure in a country like the United States are high relative to those for rail-based freight infrastructure.
Railfans commonly deride freight rail companies for delaying passenger trains, which is indeed a problem, but it's also worth remembering that they're essential to achieving net-zero emissions targets. A truly environmentally sustainable freight transportation industry is not one that relies exclusively or even mostly on electric trucks.