Service disruptions could be minimized by doing the following:
- Convert all stations from Queens Plaza to Main St to B division standards. Station lengthening can proceed with trains still in service. Shaving the platforms wouldn't require a complete shutdown either. This can be done gradually on weekends, with temporary wooden extensions used while IRT trains still operate on the line.
- Run Broadway service on the newly converted line west of Queeensboro Plaza. Close the section from Queensboro Plaza to Times Sq completely. This will require the most effort to convert, especially the river tubes, but won't adversly affect service in Queens. The R train would be diverted to 63rd St so that the entire capacity of the 60th St tubes can serve both Flushing and Astoria.
Of course this plan would still be disruptive, especially to those who use the #7 in LIC, and increased demand for the Times Square shuttle. But it can be done.