Trends in turnout in US Congressional and EP elections

Since 1979 (the year of the first EP direct elections), voter participation has generally fallen over time in both the US and EU, though the most recent US Congressional mid-term elections, in November 2018, and the most recent European Parliament elections, in May 2019, were both significant exceptions. The overall trend is consistent with a decline in participation in national elections in most G20 democracies
since 1945, from a post-war average of around 80 percent, to a figure of around 60 percent today.
In general, on both sides of the Atlantic, elections in which voters simultaneously decide who runs the executive branch of government, as well as who controls the legislature, attract a higher turnout.
The US mid-term elections, like European Parliament elections, generally see turnout which is 15 to 20 percentage points lower than in US presidential elections or in national elections in Europe, in both of which control of the executive is being determined.