We got busted by the feds twice in my 30 years or so of working. Once, IRS (but not taxes) and the other time....recently, DOT, driver doesn't carry a CDL and we weren't aware that he had to have one (our own ignorance, and that is no excuse...I know). On the CDL...I'll post a topic in "off topic".
From experience dealing with the FED, you don't win against them, at least not from a personal level. We mostly won our IRS fight but notice I said "mostly". The DOT, nope. They make up the rules however they see fit.
So from those two experiences, I don't trust the FED one bit, and honestly am a little bit paranoid and to this day still have occasional nightmares from the IRS experience. I don't like the federal government, their laws and regs, and I sure don't like the legal system that you have to use to work "with" them.
....that said...
The DPF system and DEF systems aren't EPA mandated. Tier 4 IS mandated, and Tier 4 emissions is basically a standard, which specifies (in a nutshell) how much particulate and how much NOX is emitted from a running diesel engine. How the manufacturers deal with the emission standard is up to the manufacturers. Keep in mind, Tiered emission started way back in about 1965, and was amended several times, which led up to this "garbage". Remember the 1970's emissions? Nightmare, similar to what we are seeing now but looking back, it was so simple and we got in a tizzy for...basically nothing.
Manufacturers chose the cheapest, simplest system possible that would still meet US emissions standards. In the case of this discussion, at the time when they were testing different methods, it was deemed best for everyone that the DEF and/or DPF system would be best. THat's one reason trucks use it. Big trucks that haul basically everything were hit with this stuff around 2007, and many if not all of the companies figured out that it'd add expense to maintenance and upkeep, but they didn't know how much until a few trucks were purchased and put into service. Remember, this was around 2008/9 when it finally started getting more known. Also, on/about 2008/9 we also saw the prices of fuel skyrocket, combined with higher maint/repair costs, we saw costs of everything go up (remember...basically everything we use is hauled at some point by a big truck). Now, the point here is....do you think that trucking companies like this stuff? They hate it too, but again they don't have a choice, so they've learned to deal with it. And honestly, it's not that big of a deal once the technicians figured it all out-at least enough so that they could work on them. Owners and operators also have to be educated-and this also applies to tractors!
Here is my take. Based on what I am seeing with the trucking industry, and what at least the local UPS and FEDEX drivers are doing/seeing, the expense added to the trucks have pushed some of them to get into GAS burning trucks. Most of the local residential delivery trucks are gas burners now, where it wasn't long ago, they were basically all 5.9 Cummins and 7.3 Internationals. When they because too worn out and therefore expensive to repair, they replaced them with gas engine powered trucks, which are mostly GM 6.0 engines I'm told. They aren't any great engine either but they're MUCH easier and cheaper to maintain/repair than the current production diesel trucks are. That begs the question. When are we going to see gas come back to tractors? I remember many moons ago when I had a gas tractor and then I got on a similar diesel (Ford) and the diesel outperformed the gas 5 to 1, BUT that was over 40 years ago and the technology that designs and builds things have come a LONG way (obviously)-and now we have small turbocharged gas engines that make more power and torque at a low engine speed than ever before, sometimes more torque than a diesel does in the same package (but at slightly more fuel usage). I believe that there is a market for it. I spoke with a Kubota engineer and they wouldn't confirm or deny that they've thought of it or tested anything but at the very least, I planted that seed in their brains. Maybe it'll grow, maybe it's a dud-but time will tell.
But until the "roll back" and "gas" happen, we have to deal with this stuff, and hopefully we do it legally. Don't mess with the Fed's because the fines for this stuff aren't cheap, and I personally know of at LEAST one company who lost their business over a fleet of "deleted" pickup trucks. Sure they were enjoying a 2-5 mpg improvement and a reduction in their cost in the form of maintenance/repair but they paid for it MANY times over in the form of fines, and the ultimate loss of their quite profitable business. Farmers take note.