For voters with "social" preferences, the expected utility of voting is approximately independent of the size of the electorate, suggesting that rational voter turnouts can be substantial even in large elections. Less important elections are predicted to have lower turnout, but a feedback mechanism keeps turnout at a reasonable level under a wide range of conditions. The main contributions of this paper are: (1) to show how, for an individual with both selfish and social preferences, the social preferences will dominate and make it rational for a typical person to vote even in large elections; (2) to show that rational socially-motivated voting has a feedback mechanism that stabilizes turnout at reasonable levels (e.g., 50% of the electorate); (3) to link the rational social utility model of voter turnout with survey findings on socially-motivated vote choice.