Sheriff Road–River Terrace Line

Route U4 provides daily service between Minnesota Avenue station and Sheriff Road NE & Lee Street NE (Sheriff Road) or 33rd Street NE & Blaine Street NE (River Terrace). Because the U4 route is a short Metrobus route with low passenger demand, U4 has almost always been assigned the smaller sized 30-foot buses, as opposed to the regular 40-foot sized buses WMATA typically uses on many of its Metrobus routes. However, route U4 occasionally uses 40 ft buses if the 30 ft buses are undergoing maintenance.

Route U4 operates out of Bladensburg division.

U4 originally operated as part of the "Sheriff Road-River Terrace" streetcar line, between the Deanwood & River Terrace neighborhoods of Northeast Washington D.C. The U4 streetcar line was later replaced by buses during the 1950s and eventually became a WMATA Metrobus Route on February 4, 1973 when WMATA acquired all four bus companies that operated throughout the Washington D.C. Metropolitan Area and merged them all together to form its own, "Metrobus" System. U4 kept operating on the same exact streetcar routing it had been operating on since 1949, even after becoming a WMATA Metrobus Route.{{Cite web|url=https://www.chicagorailfan.com/wasdated.html|title=WASHINGTON DC TRANSIT ROUTES|website=www.chicagorailfan.com|access-date=2019-11-10}}

On December 3, 1978, U4 went through a minor rerouting change to divert into/serve the newly opened Minnesota Avenue station. The rest of U4's routing remained the exact same.{{Cite news|url=https://www.washingtonpost.com/archive/local/1978/11/30/bus-routes-change-sunday-to-link-with-orange-line/74b7bfbd-4100-411b-b9eb-d51f9e4a0031/|title=Bus Routes Change Sunday to Link with Orange Line|last=Feaver|first=Douglas B.|date=1978-11-30|work=Washington Post|access-date=2019-11-10|language=en-US|issn=0190-8286}} The line was named the Minnesota Avenue Shuttle.

On January 22, 1984, route U4 was rerouted to operate between Sheriff Road and Capitol View passing Minnesota Avenue station in both directions.{{cite web |last1=Leslie |first1=Renee T. |title=Metro Sets Shuttle Bus Link For SE Residents |url=https://www.washingtonpost.com/archive/local/1984/01/12/metro-sets-shuttle-bus-link-for-se-residents/46ba25bb-e8c4-4c2c-acaf-4a438b67a369/ |website=Washington Post |accessdate=21 June 2020 |date=12 January 1984}}

In 2014, WMATA announced a series of proposals for route U4 that will be implemented in June 2015 if it was approved by the Metro Board. It went as the following:{{cite web |title=DISTRICT OF COLUMBIA PROPOSED BUS SERVICE CHANGES |url=https://www.wmata.com/about/public-hearings/upload/DC_Docket.pdf |website=www.wmata.com |accessdate=5 May 2020}}

• Route U4: Daily service at all times between River Terrace and Deanwood Station via the current route between River Terrace and Minnesota Avenue station, then via the current route of V7 and V8 from Minnesota Avenue Station to Deanwood station.
• Route U4 would no longer serve the portion of the current route between Minnesota Avenue Station and Sheriff Road.
• New Route U7 would serve the portion of the current route between Minnesota Avenue Station and Sheriff Road.

This rerouting was to create a better balance of capacity and demand on lines serving the Minnesota Avenue station.

During the COVID-19 pandemic, Route U4 was reduced to operate on its Saturday supplemental schedule during the weekdays beginning on March 16, 2020.{{cite web |title=Metro announces additional COVID-19 changes, including reduced service beginning Monday {{!}} WMATA |url=https://www.wmata.com/about/news/Metro-announces-additional-COVID-19-changes.cfm |website=www.wmata.com |access-date=31 January 2021}} On March 18, 2020, the line was further reduced to operate on its Sunday schedule.{{cite web |title=METRO SERVICE LEVELS & HOURS FURTHER REDUCED TO SUPPORT ESSENTIAL TRIPS ONLY, STARTING WEDNESDAY {{!}} WMATA |url=https://www.wmata.com/about/news/METRO-SERVICE-FURTHER-REDUCED-TO-SUPPORT-ESSENTIAL-TRIPS-ONLY.cfm |website=www.wmata.com |access-date=31 January 2021}} Weekend service was later suspended on March 21, 2020.{{cite web |title=Weekend: Metro service limited to 26 bus routes, reduced rail service; expect wait times of 30 minutes; customers urged to travel only if essential {{!}} WMATA |url=https://www.wmata.com/about/news/Weekend-service-3-28-3-29.cfm |website=www.wmata.com |access-date=31 January 2021}} Service was restored to its pre-pandemic schedule on August 23, 2020.{{cite web |title=August 2020 Metrobus Service Changes, August 23 {{!}} WMATA |url=https://www.wmata.com/service/status/details/proposed-august-2020-metrobus-service-changes.cfm |website=www.wmata.com |accessdate=28 July 2020}}

In February 2021 during the FY2022 budget, WMATA proposed to eliminate the U4 if it does not get any federal funding.{{cite web |title=FY22 Proposed Metrobus Service Changes District of Columbia |url=https://www.wmata.com/initiatives/budget/upload/Proposed-DC-Bus-Changes.pdf |access-date=25 March 2021}}

As part of WMATA's Better Bus Redesign taking place on June 29, 2025, the U4 was renamed into the C33, keeping its same routing.{{cite web |title=Metro Board of Directors approves Better Bus Network Redesign, new bus routes to start next summer |url=https://www.wmata.com/about/news/Metro-Board-of-Directors-approves-Better-Bus-Network-Redesign-new-bus-routes-to-start-next-summer.cfm |website=WMATA |access-date=23 January 2025 |language=en}}

• On September 5, 2017, a passenger was arrested after he spat on a U4 bus driver along Minnesota Avenue. The driver was taken to a hospital.{{cite web |last1=Marraco |first1=Marina |title=Passenger arrested for spitting in the face of Metrobus driver |url=https://www.fox5dc.com/news/passenger-arrested-for-spitting-in-the-face-of-metrobus-driver |website=FOX 5 DC |accessdate=20 May 2020 |date=5 September 2017}}{{cite web |last1=Powers |first1=Martine |title=In latest assault on a bus operator, passenger spits on U4 driver |url=https://www.washingtonpost.com/news/dr-gridlock/wp/2017/09/06/in-latest-assault-on-a-bus-operator-passenger-spits-on-u4-driver/ |website=Washington Post |accessdate=20 May 2020 |language=en}}

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U4