Virginia held two elections for U.S. House, 7th district, on November 4, 2014. One was for the regular two-year term and the other was for the short term running from November 2014 to early January 2015. The need for the short term special election was because the seat was vacant, because Congressman Eric Cantor had resigned earlier this year, before his term was up.
The Democratic and Republican nominees for both November 2014 elections were the same two individuals. But the regular election had a Libertarian on the ballot, whereas the special election only had the two major party nominees.
The vote in the regular election was: Republican Dave Brat, 148,026; Democrat John K. Trammell, 89,914; Libertarian James A. Carr, 5,086; miscellaneous write-ins 325.
The vote in the special election was: Brat 148,841; Trammell 91,236; miscellaneous write-ins 1,236.
Because the two major party nominees were the same individuals in both races, this juxtaposition of two elections gives evidence of how most voters who vote Libertarian (at least in this part of Virginia) would vote, if no Libertarian were on the ballot. It appears that probably 26% of Carr’s voters voted Democratic in the special election which didn’t list Carr; 16% voted Republican; and the other 58% of Carr’s voters either cast a write-in vote, or chose not to vote in the special election. Here is a link to the Virginia State Board of Elections’ web page showing election returns.