Back Bay Station to Union Square, Somerville
How to get from Back Bay Station to Union Square, Somerville on public transit, with the stops, times and the last trip of the night.
Back Bay Station to Union Square, Somerville
- Orange Line
- Bus 109
- Take the Orange LineFrom Back Bay, toward Oak Grove8 stops, about 12 min
- Change at Sullivan Square
- Take bus 109Toward Harvard via Sullivan7 stops, about 8 min
- Get off at Somerville Ave @ Union SqThe stop after Washington St @ Boston St
Weekdays, fall 2026 schedule · First and last trips
Quick answer: Take the Orange Line toward Oak Grove to Sullivan Square, then bus 109 to Somerville Ave @ Union Sq. The trip takes about 30 minutes (26-32 min depending on the connection). On weekdays bus 109 runs about every 15 min during the day.
Get the live route from Back Bay to Union Square
Step by step
- At Back Bay, take the Orange Line toward Oak Grove.
- Ride 8 stops, about 12 min. Get off at Sullivan Square, the stop after Community College.
- At Sullivan Square, change to bus 109 toward Harvard via Sullivan.
- Ride 7 stops, about 8 min. Get off at Somerville Ave @ Union Sq, the stop after Washington St @ Boston St.
Other ways to go
- Take the Orange Line toward Oak Grove to North Station, then the Green Line to Union Square, and walk about 7 min: about 34 min.
- Take the Orange Line toward Oak Grove to Sullivan Square, then bus 85 to Somerville Ave @ Union Sq: about 29 min.
Which one is faster depends on when you leave. Cobblehop compares them with live times and gives you the one that gets you there first.
Times and frequency
| Day | First trip | Last trip | How often (daytime) | Trip time |
|---|---|---|---|---|
| Monday-Thursday | 5:05 am | 12:57 am | About every 15 min | About 30 min |
| Friday | 5:05 am | 1:47 am | About every 15 min | About 30 min |
| Saturday | 5:20 am | 1:52 am | About every 15 min | About 29 min |
| Sunday | 5:59 am | 12:51 am | About every 15 min | About 28 min |
First and last trip are when the first train of the trip leaves Back Bay, on the fall 2026 schedule. "How often" is for bus 109 (the least frequent part of the trip).
Late at night
On weekdays, the last trip that works leaves Back Bay at 12:57 am and gets to Union Square, Somerville around 1:30 am, using Green Line and bus 109. On Friday nights it runs later: the last trip leaves at 1:47 am. On Saturday nights the last trip leaves at 1:52 am, and on Sunday nights at 12:51 am. Late at night, ask Cobblehop for the last trip. It checks live times and tells you when to leave.
Tips for this trip
- Know your stop. Get to the door after Washington St @ Boston St. The next stop is Somerville Ave @ Union Sq. Start a live trip in Cobblehop and it alerts you before your stop.
- Changing at Sullivan Square. You don't leave the station. Follow the signs for bus 109.
- Union Square station is the end of the Green Line D branch, a short walk from the square.
- Back Bay station has the Orange Line, Commuter Rail and Amtrak under one roof. It connects to Copley Place by an indoor passage.
Step-free access
MBTA data lists every station on this route (Back Bay and Sullivan Square) as accessible. Back Bay has 4 elevators in MBTA data. Elevators do break, so check the MBTA's elevator alerts before you go.
What it costs
- Subway and bus. The subway is $2.40 one way, and a local bus is $1.70. Under an MBTA pilot that started September 1, 2026, you can change between bus and subway within 2 hours of your first tap and pay only the highest fare, if you use the same card or phone each time.
- How to pay. Tap a contactless credit or debit card, phone or watch at the fare gate or bus door, or use a CharlieCard or CharlieTicket.
- Kids. Children 11 and under ride the MBTA free.
Fares as of October 2026. Check the MBTA's fares page before you ride.
Back Bay Station to Union Square, Somerville: common questions
How do I get from Back Bay Station to Union Square, Somerville by public transit?
Take the Orange Line toward Oak Grove to Sullivan Square, then bus 109 to Somerville Ave @ Union Sq. The trip takes about 30 minutes (26-32 min depending on the connection).
How long does it take to get from Back Bay Station to Union Square, Somerville?
About 30 minutes on the main route, or 26-32 minutes depending on the connection.
Do I have to change along the way?
Yes, once: at Sullivan Square. Take the Orange Line toward Oak Grove to Sullivan Square, then bus 109 to Somerville Ave @ Union Sq.
How often does bus 109 run?
About every 15 min on weekdays during the day, about every 15 min on Saturdays and about every 15 min on Sundays, on the fall 2026 schedule.
What time is the last train from Back Bay Station to Union Square, Somerville?
On weekdays, the last trip that works leaves Back Bay at 12:57 am and gets to Union Square, Somerville around 1:30 am, using Green Line and bus 109. On Friday nights it runs later: the last trip leaves at 1:47 am. On Saturday nights the last trip leaves at 1:52 am, and on Sunday nights at 12:51 am.
Related routes
- Back Bay Station to Inman Square
- Back Bay Station to Cambridge Hospital
- Boston Common to Union Square, Somerville
- Kendall Square to Union Square, Somerville
- Never miss your stop (guide)
More routes from Back Bay Station
- Back Bay Station to Central Square, Cambridge
- Back Bay Station to Harvard Art Museums
- Back Bay Station to Harvard Museum of Natural History
- Back Bay Station to MIT Museum
- Back Bay Station to MIT
- All routes from Back Bay Station
Official sources
Cobblehop is independent and isn't affiliated with these agencies or operators. Schedules on this page come from MBTA/MassDOT public data. Check their pages for the latest schedules and service changes:
- MBTA: Orange Line
- MBTA: bus 109
- MBTA: Back Bay station
- MBTA: Sullivan Square station
- MBTA: fares
- MBTA: elevator and accessibility alerts
Published October 30, 2026. Times were computed from the fall 2026 MBTA schedule (2026-11-04 for weekdays). Service changes, so check Cobblehop for live times before you go.
Leaving now? Cobblehop gives you one clear plan with live times and alerts you before your stop. No sign-up, nothing to install.