Semi truck markings and license plate questions - history thereof

Factual Questions
1

It’s surprisingly hard to find the answer to my questions. I can get tons of sites telling me how to install the marking, which markings are correct, what they mean - but the history is obscured.

When were trucks first required to use red and white reflective tape? My memory says it was about 1999-ish?

When were trucks first required to use the four digit UN code for hazardous cargo? I remember when tanks trailers were labeled “HAZARDOUS CHEMICALS” and whatnot, and fire departments were left to fend for themselves to figure out what actually was in the trailer. Now we have the UN code, which makes it easy. But. when did we switch over?

When did trucks switch from many license plates to one single “apportioned” license plate? The 1990s?

Then:

Now:

2

Googling round, it gets confusing. The relevant regulation seems to be 49 CFR 390.21 - Marking of self-propelled CMVs and intermodal equipment. October 1, 2011.

However, I also read this: At 82 FR 5316, Jan. 17, 2017, § 390.21 was suspended, effective Jan. 14, 2017. At 84 FR 40294, Aug. 14, 2019, the suspension was lifted and amendments were made to § 390.21. In that same document, § 390.21 was again suspended indefinitely.

3

One more bump for visibility, in case anyone knows.

4

2011?

https://www.federalregister.gov/documents/2011/01/19/2010-33324/hazardous-materials-harmonization-with-the-united-nations-recommendations-international-maritime

5

I’m guessing that part of the uncertainty might be due to some regulations being first implemented by various states, before being set nationally by the federal government. So for some period of time, you’d have some trucks (those that at least partially operated in those states) with the new markings, and some without.

6

For the most part, yeah. The government-sponsored organization responsible for this started with three states – Kentucky, Missouri, and Tennessee – in '73 and went national in the US & Canada in '91.