But although there have been a few high-profile flameouts, that shouldn’t obscure the fact that well-established mainline suppliers of heavy Class-8 trucks have also been investing significantly in an effort to go electric. The technology is advancing quickly. There are significant economic advantages to the electric powertrain, including mechanical simplicity, greater longevity, and reduced fuel costs in addition to the obvious ecological, emissions and climate change benefits. The operating costs of an all-electric truck are potentially much lower than that for a diesel truck.

However, big obstacles remain. These include the initial cost of the batteries, inadequate range, lack of a comprehensive charging network, and the time required to recharge. But all of these problems can be addressed. The most significant and intractable problem is that of energy density or, to put it another way, weight.

Energy density is the measure of how much energy is contained within a given volume or weight. A relatively small amount of diesel contains a vast quantity of energy compared with a battery. A gallon of diesel contains somewhere between 50 and 126 times the energy per pound than the equivalent weight of advance lithium-ion battery power. Adding in the weight of the battery protection and support structure versus that of the fuel tank further adds to the differential. On the other hand, the electric powertrain is much more efficient than the internal combustion engine, which helps reduce the problem. An internal combustion engine can convert perhaps 35 percent of the fuel’s energy into productive work, while the electric powertrain makes use of 90 percent and more. That reduces the weight comparison from 50 times the fuel weight down to 20 times.

A truck achieving a typical fuel efficiency of 6.5 mpg requires 77 gallons of diesel to travel 500 miles weighing 540 pounds. At a 20:1 ratio, that works out to 10,800 pounds of batteries. In other words, batteries are heavy. The battery array needed to power a Class-8 tractor weighs thousands of pounds, making the tractor much heavier than its fossil-fueled counterpart. This is extremely problematic because it reduces the payload capacity of the rig, resulting in large adverse effects of the economics of conversion. Even assuming that batteries continue to improve (energy density has tripled in the last few years according to Bloomberg News) and that the weight differential is cut in half, that’s still 5,000 to 6,000 pounds of additional weight, representing a payload loss of about 12 percent on a heavy load. That is a huge disability to overcome which will impair the speed of the transition, moving the zero-emissions goal further out in the future.

But what if the federal government decided to use payload as an accelerant? What if zero-emission vehicles were allowed a higher gross weight on the highway than fossil-fueled units? A disability would be turned into an asset. Instead of the heavy hand of regulation forcing the transition, the power of economics and efficiency will work together to pull it through.

There are examples of this to be found elsewhere. For instance, in Europe, the standard highway gross vehicle weight limit is 40 metric tonnes, but if the unit is being used for a combined transport (i.e. intermodal) movement, the GVW limit is bumped up 10 percent to 44 metric tonnes, as a means of encouraging the use of intermodal and improving its economics.

As an innovation accelerant, the federal government could allow a GVW of 97,000 pounds on six axles for zero-emission vehicles. The requirements could also state that the vehicle would need to be equipped with the latest safety innovations, such as lane departure, automatic emergency braking, collision avoidance, and the like.

This plan would require a balancing of costs and benefits across several dimensions. While the green benefits are obvious, highway safety advocates might opt to fight the plan. But should they? Assuming a maximum load and a standard 12,000 pound limit on the steer axle of both units, the weight on each of the remaining axles is identical — 17,000 pounds. The braking performance of the two units would therefore be identical, and that’s before we factor in the enhanced safety gear required on the zero-emission unit.

Innovation happens fastest when the power of economics is brought to bear. Coal emissions were reduced due to environmental regulations. But even as those regulations have been rolled back by the current administration, coal use has plummeted ever faster because natural gas has become cheaper.

Similarly, a creative approach toward incentivizing green technology could result in a substantial acceleration in the adoption of cleaner heavy-duty trucks.