Route 150 is a bus route operated by the Maryland Transit Administration in Baltimore, Ellicott City, and Columbia, Maryland. The line currently operates between the Village of Harper's Choice in Columbia and downtown Baltimore, mostly via US-29 and US-40, serving The Mall in Columbia and Catonsville
In 1898, service operated by the Columbia and Maryland Railway began between Baltimore and Ellicott City. The intention was to operate a passenger railroad service between Baltimore and Washington. But it was never extended to any location past Ellicott City. The line was operated as Route 14 until 1927, when service to Ellicott City was redesignated Route 9. The No. 9 Streetcar operated between Ellicott City and Baltimore up until 1952, when it was shortened to a shuttle that operated between Ellicott City and Catonsville only. The shuttle streetcar service lasted until 1955, when it was converted into a shuttle bus. The shuttle bus operation was discontinued in 1957.
Later, Route 929, a commuter bus route marketed as a service for Columbia to Washington commuters, operated several trips each day that originated in Baltimore, and operated to Columbia through Ellicott City before continuing to Washington. Though printed in the schedules, this line was not advertised for this purpose.
Route 12 started providing express service from both the western and eastern suburbs of Baltimore in 1972. The west side service operated from a park-and-ride lot on US-40 near Westview Mall, and the eastern end service from one on Eastern Boulevard known as the Essex Park-and Ride. In 1991, the no. 12 line was redesignated, and west side service was renamed to "Route 150" and east side service to Route 160.
Neither Route 12 nor Route 150 were ever intended to serve Howard County. Route 150's origin would later be moved to the intersection of US-40 and Rolling Road. Selected trips also operated from near Security Square Mall, but these were eliminated in 1995. During the early 2000s, the line was eventually extended to the Long Gate Park-and-Ride lot in Ellicott City (near US-29 and Maryland Route 103), with two-way service during rush hour to allow for reverse commuters who worked in Ellicott City and the second connection between MTA to Howard Transit, the other being at BWI Airport, where the Light Rail and Bus Route 17 meet Howard Transit's Silver Line.
In 2005, as part of the Greater Baltimore Bus Initiative, MTA proposed to completely eliminate Route 150, and not to provide any bus service to Ellicott City, requiring riders who wished to reach Ellicott City from Baltimore to spend several hours each way on buses. The line at the time was reported as having 143 daily riders, and had required a taxpayer subsidy of $8.71 per boarding, and was seen as a "failed experiment." Due to public outcry, four round trips each day (two AM and two PM) were retained and operate to this day.
In 2009, Route 150 was extended to Columbia. On January 12, Route 311 between Columbia and Baltimore was discontinued, and Route 150 was extended to Columbia Mall. On February 8, the line was extended to the Village of Harper's Choice.