US National Peak Oil Clobbered Tetraethyl Lead

The US CDC ATSDR states that 1970 was the peak year for tetraethyl lead in gasoline.

Toxicological Profile for Lead - Section 8 Regulations and Advisories. 

By 1988, the total lead usage in gasoline had been reduced to <1% of the amount of lead used in the peak year of 1970 Superfund Amendments and Reauthorization Act (SARA) (EPA 1996a).

But the EPA etc. didn't do anything about reducing tetraethyl lead use in 1971.  US National peak oil and the third Middle East oil embargo against the US did that.

In Jan 1973 the EPA ruled that by 1974 unleaded gas was to be available. In Dec 1973 they ruled that lead had to start being phased down. This fails to account for lead levels falling from 1970 to 1973. The fact that tetraethyl lead usage did not increase in 1971, 1972 and 1973 must have had a cause since until then every year brought more cars and more gasoline.

This paragraph from the EPA shows the timeline for the phase down:

US EPA Persistent Bioaccumulative and Toxic (PBT) Chemical Program
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6.2.1 Regulations Controlling Use

In the early 1970s, EPA issued two regulations under the statutory authority of the 1970 Clean Air Act (CAA). First, EPA required major gasoline retailers to begin selling one grade of unleaded gasoline by July 1, 1974. This mandate was primarily focused on preventing the deterioration, as a result of leaded gasoline, of emissions control systems (e.g., catalytic converters) in motor vehicles so equipped. In developing these regulations, EPA first established the working definition of "unleaded" gasoline as "gasoline containing not more than 0.05 gram of lead per gallon and not more than 0.005 gram of phosphorus per gallon" [38FR1255, January 10, 1973]. Second, EPA issued a regulation calling for the gradual phase-out of leaded gasoline. The schedule for reduction of lead content in automobile gasoline was 1.7 grams per gallon (g/gal) in 1975, to 1.4 g/gal in 1976, 1.0 g/gal in 1977, 0.8 g/gal in 1978, and 0.5 g/gal in 1979 [38FR33741, December 6, 1973]. Subsequent regulations reduced the allowable lead content to 0.1 g/gal in 1986 [50FR9397, March 7, 1985], and prohibited leaded gas use after 1995 [61FR3837, February 2, 1996].

That article quotes Federal Regulations (the ##FR#### codes) that can be seen here: Electronic Code of Federal Regulations - PART 80—REGULATION OF FUELS AND FUEL ADDITIVES US National peak oil happened in December 1970, the most productive month of all time at 308,264,000 barrels/month. See US DOE EIA - U.S. Field Production of Crude Oil
The third Middle East embargo came online in October 1973

The Oil Weapon and American Foreign Policy - Dr. Joseph S. Szyliowicz Major Bard E. O’Neill
... the decision by the Organization of Arab Petroleum Exporting Countries (OAPEC) in October 1973 to decrease the production of crude oil and to embargo the U.S. ...