This corridor was previously served by Metro routes 15 and 18, which carried a combined average of 7,630 riders on weekdays during the last month in service. On , the D Line began service, running between
Carkeek Park in
Crown Hill,
Ballard,
Interbay,
Uptown, and
downtown Seattle. In 2014, the city of Seattle planned major improvements to the RapidRide C and D lines after their opening with funds generated by Proposition 1 (which increased sales tax by 0.1 percent and imposed a $60 annual car-tab fee). In June 2015, the first improvements came when headways on the RapidRide C and D lines were improved. Buses arrive every 7–8 minutes during weekday rush hour; every 12 minutes during midday hours on weekdays, and during the daytime on Saturday; and every 15 minutes on Sundays and during all nights. Since the implementation of RapidRide on the corridor, ridership has grown 53 percent, and the D Line served an average of 11,700 riders on weekdays in spring 2015. terminating on Valley Street near the
Fred Hutchinson Cancer Research Center campus. D Line buses instead continue south on 3rd Avenue into
Pioneer Square, using
layover space on 5th Avenue south of Terrace Street. ==Service==