In the mid-1990s, the MTA discovered that the Queens Boulevard viaduct structure was unstable, as rocks that were used to support the tracks as ballast became loose due to poor drainage, which, in turn, affected the integrity of the concrete structure overall. <7> express service was suspended again between 61st Street–Woodside and Queensboro Plaza; temporary platforms were installed to access the express track in the four intermediate stations. The work began on April 5, 1993. When the viaduct reconstruction finished on March 31, 1997, ahead of schedule, full <7> express service was reinstated. Throughout this entire period, ridership grew steadily.