Except for an occasional truck rodeo, the era of rolling black coal and soot-lined exhaust stacks is behind us.

Exhaust gas recirculation (EGR) systems slashed smog-producing NOx. Diesel particulate filters followed, capturing flakes that would otherwise burrow into lungs. Then came the selective catalytic reduction and diesel exhaust fluid that pushed NOx even lower. Boosts in fuel economy, when they were possible, limited greenhouse gases.

They’re the changes and tweaks that improve local air quality and help fight climate change. Admirable goals to be sure.

To say it’s been a difficult journey would be an understatement, of course. The related targets – especially those that required all-new technologies — introduced engineering challenges and maintenance headaches alike. EGR coolers cracked. Valves failed. Pitot tubes plugged. Diesel particulate filters clogged. NOx sensors “drifted”.

Even where these technical pains have eased, fleets and owner-operators continue to bear the costs of higher sticker prices, additional maintenance requirements, and downtime.

New truck emissions rules coming

And if you think this journey is over, think again. There’s little relief on the horizon as regulators push for evermore emissions-related improvements. Trucks still contribute a significant share of on-road emissions.

But it is possible to push things too far, too fast. When emerging technology is deemed too costly or problematic, fleets “pre-buy” equipment before regulatory changes take hold or keep older technology in service longer than originally planned. Such decisions delay the emissions-related improvements that regulators supposedly desire.

Emerging regulations and timelines south of the border – and likely to be introduced here – threaten to create these very conditions.

Some of the NOx standards unveiled this December rely on unproven or unavailable technologies. Suppliers will be expected to create things like a new generation of NOx sensors even as regulators promote zero-emission alternatives – an environment that hardly encourages investments. And emissions systems will have to carry warranties that are as much as 4.5 times longer than those in place today, to help ensure the systems work optimally over the “useful life” of a truck.

How much will low-NOx engines cost?

Initial purchase prices for trucks are expected to increase US$35,000 in the process. And new maintenance requirements will likely emerge as manufacturers look to make the extended warranties a reality.

Once again, truck owners will be the ones to pay the price.

The California Air Resources Board (CARB) wants to push matters further, slashing NOx emissions by 90% and cutting particulate matter in half. Several states are following that lead, certainly affecting truckers who run there, and likely forcing manufacturers to focus on building models that meet the tightest rules. To compound matters, ongoing discussions about further reducing greenhouse gases are at odds with efforts to reduce NOx.

It’s clear that regulators want diesel engines to be relegated to the dustbin of history. Set the standards tough enough, and timelines tight enough, it eventually becomes impossible to build an economically viable engine. Time will tell if the latest standards and timelines ultimately bring us to that point.

But even if that is the ultimate finish line, regulators need to recognize the current limitations of zero-emissions equipment when establishing their targets and timelines.

In the words of Canada’s Action Plan for Clean On-Road Transportation: “Zero-emission technologies for medium- and heavy-duty vehicles are less commercially ready than for light-duty vehicles and significant barriers exist that could slow adoption, including inadequate charging and refueling infrastructure in both private and public settings.”

Canada has about 2.6 million medium- and heavy-duty vehicles. They won’t stop burning fuel overnight.