Create a simple 'time test' that every ballot in the country must be put through to find out the time it takes the average voter to complete. Multiply that time by the number of registered voters in the precinct. Divide that time by the number of hours allotted for voting. There you have it - an easy method to determine the required number of voting machines (and corresponding poll workers) per precinct. No more long lines, no more concerns about voter suppression.
Alternatively, change to the system of vote-by-mail following Oregon's lead. Also eliminates the problem.