The equivalent figure of 2016 138 Million - a 58.1% turnout. Thus a 170 Million turnout would represent a  23% increase. Most estimates for projected 2020 turnout I have seen are around the 150 Million mark, a more modest 8.7% increase.

Turnout over the last 100 years has been in the 50-63% range.

Index of Frank's Diaries

AP wants to reclaim 170-year-old authority from electproject with "undervotes" reported by stringers with eyes on county clerks.
Millions of mail ballots not yet returned in key states, 28 Oct

At least 35 million mail ballots had been returned or accepted as of early Wednesday, according to data collected by The Associated Press. That surpasses the 33.3 million total mail ballots returned during the 2016 election, according to the U.S. Election Assistance Commission.

versus 51,246,523 + walk-ins

For a number of reasons, past absentee ballot volume isn't a useful benchmark of "turnout". AP is not the only news publisher with difficulty adjusting to this multi-modal, disease-ridden, 40-day+ "Election Day".  

How the U.S. early vote surge is shaping Trump, Biden endgames

Across the 20 states that publish the party registration of ["]early["] voters, more than 17.4 million registered Democrats had voted by Wednesday compared with 10.8 million registered Republicans, according to figures compiled by the U.S. Elections Project at the University of Florida.

electproject prints 27,349,231 "in-person" ballots (NAME visible, gov ID), 51,246,523 "mail ballots" (NAME visible, envelope window) returned a/o 29 Oct. NAME is the only way to associate voter with PARTY registration in state database records...and arrest duplicate new and old  entries.

About 47 million Americans who have voted so far either are not affiliated with a party or live in a state that does not publicly report a voter's party affiliation.

What message is this publisher attempting to communicate with a string of non sequiturs?

More than 75 million Americans had already cast ballots as of Wednesday. That's by far the most-ever in early voting, and it's more than half the final turnout of 138 million votes recorded in the 2016 election. The STAGGERING figures have prompted some analysts to predict the highest turnout rate in a century.

61.65% registered voters, 2008. 228M eligible (VAP), 153M registered, or 66.9%2018

The actual votes for each candidate won't be known until polls close, perhaps with a lag of days or more.