Most voting experts are not predicting a repeat of the Florida meltdown of 2000, but they are warning that shortages of electronic voting machines or printed ballots in swing states, along with problems verifying the identity of voters, could worsen lines and fray nerves.  “What has traditionally happened in this country is that a change in voting equipment happens once in the lifetime of an election official,” said Kimball W. Brace, president of Election Data Services, a voting research firm. “This time, nearly 60 percent of the country will vote in places that in the last eight years have changed their voting equipment.”  About a fourth of voters will still use electronic machines that offer no paper record to verify that their choice was accurately recorded, even though these machines are vulnerable to hacking and crashes that drop votes. The machines will be used by most voters in Indiana, Kentucky, Pennsylvania, Tennessee, Texas and Virginia. Eight other states, including Georgia, Maryland, New Jersey and South Carolina, will use touch-screen machines with no paper trails.  In states with early voting, there have been scattered reports of touch-screen machine malfunctions, ballot misprints causing scanners to jam and vote-flipping, in which the vote cast for one candidate is recorded for another.  Florida has switched to its third ballot system in the past three election cycles, and glitches associated with the transition have caused confusion at early voting sites, election officials said. The state went back to using scanned paper ballots this year after touch-screen machines in Sarasota County failed to record any choice for 18,000 voters in a fiercely contested House race in 2006.  Voters in Colorado, Tennessee, Texas and West Virginia have reported using touch-screen machines that at least initially registered their choice for the wrong candidate or party.  “I pushed the Democrat ticket, and it jumped to the Republican ticket for president of the United States,” said Calvin Thomas, 81, an Obama supporter who tried to vote early in Ripley, W.Va. “I’m a registered Republican, and I’ve voted in every presidential election since 1948. I don’t like seeing my vote do something I didn’t tell it to do. I take that real serious.”  Mr. Thomas’s daughter, Micki Clendenin, said the same thing had happened to her.  In both cases, poll workers at the site had them touch the screen a few more times, and the voting machine changed their ballot to their candidate choice. State and local officials said these were isolated cases and that poll workers had fixed the problems.  “It was corrected,” Ms. Clendenin said, “but it still made me wonder.”  It was not supposed to be this way.  After the debacle of 2000, Congress passed a federal law, the Help America Vote Act, to avoid similar mishaps. It included money for new machines to modernize the voting process. But in many ways, things have become even messier. The first machines bought with the federal money were largely touch-screens and brought new problems, decreasing public confidence in the process and doubling the number of election-related lawsuits since 2000.  In the past two years, the pendulum has swung away from electronic machines, but the change has come during one of the most dramatic presidential elections in modern history.  “Counties and states are better prepared for machine problems than they have been in the past,” said Lawrence Norden, a voting expert with the Brennan Center for Justice at the New York University School of Law. “Problem is that this election may not be like any other in terms of the strain on the system, and small problems can have big consequences when there are such tight margins and so many people showing up to vote.”  Most states have passed laws requiring paper records of every vote cast, which experts consider an important safeguard. But most of them do not have strong audit laws to ensure that machine totals are vigilantly checked against the paper records.  Last year, a study by the Brennan Center found that at least 17 of the 38 states with paper records did not require audits after every election. The states with audits do them inadequately, the report found.  In Ohio, Secretary of State Jennifer Brunner sued the maker of the touch-screen equipment used in half of her state’s 88 counties after an investigation showed that the machines “dropped” votes in recent elections when memory cards were uploaded to computer servers.  As an extra precaution, Ms. Brunner required all counties to provide paper ballots to anyone who wanted to use them.  On Wednesday, a federal judge ordered election officials in Pennsylvania to make emergency paper ballots available to voters when 50 percent or more of voting machines at a polling location fail. Previously, these ballots would be available only if all the machines at a polling place broke down.  A report released last month by several voting rights groups found that eight of the states using touch-screen machines, including Colorado and Virginia, had no guidance or requirement to stock emergency paper ballots at the polls if the machines broke down.  A version of this article appears in print on , on Page A21 of the New York edition with the headline: Voting Experts Say High Turnout May Add to Problems at the Polls. Order Reprints| Today's Paper|Subscribe
Six years after an overhaul in how elections are run, voting experts still predict machine and ballot shortages and late tallies.