Starting Monday, June 5, Sound Transit is putting more three-car light rail trains into weekday service to meet increasing demand and prepare for expected peak summer crowds.

Link carried an average of 71,300 riders on weekdays in April, a 17 percent increase over 2016, according to Sound Transit. April was the first full month to compare year-over-year ridership since new Link stations on Capitol Hill and at the University of Washington opened in March 2016.

Based on past performance, ridership is expected to continue climbing this summer during the peak Seattle tourist season. So transit officials will boost weekday capacity to meet growing demand.

Sound Transit will start the day at 5 a.m. with 12 three-car trains and add seven more two-car trains during peak hours. Currently it begins the day with 12 two-car trains and adds seven three-car trains during peak hours. Around 6:30 p.m. the three-car trains will start coming offline for daily maintenance and cleaning so they’re ready for service the next weekday. The seven two-car trains will stay online until service stops at 1 a.m. for overnight station and tunnel maintenance.

The agency will adjust evening train sizes and deploy additional trains as needed to accommodate special events like evening Sounders FC or Mariners games.

It’s a tricky balancing act to meet booming rush-hour demands without running more service than needed during off-peak hours and incurring higher maintenance costs from additional wear and tear, according to Sound Transit. Just like other busy rail systems around the world, the agency sizes its fleet and service levels to carry at least as many people standing as seated during the busiest times.

However, by monitoring trip-level ridership during the past few months, Sound Transit has seen heavy train loads stretching beyond traditional rush hours with some rush-hour trips nearing maximum capacity. The latter case is especially true when there is any sort of delay in the congested Downtown Seattle Transit Tunnel that causes missed train trips. When that happens, it can take several follow-up trains to clear rush-hour platforms.

Add to these considerations that summertime has traditionally been Sound Transit’s busiest time for riding Link when it sees steady demand throughout the day, not just during rush hours.