Rock Creek Park is part of the National Park System. In August 2019 regulations came into effect allowing e-bikes on designated paths in national parks, including Rock Creek Park.

The Peirce Mill in Rock Creek Park. Milling demonstrations are held from 11 AM to 2 PM on the second and fourth Saturday of each month starting in April and running through October.
Does that mean that e-biking is allowed in Rock Creek Park?
E-biking is allowed in Rock Creek Park where other types of bicycles are allowed and prohibited where other types of bicycles are prohibited.

A map of Rock Creek Park produced by the National Park Service. Cycling and e-biking is allowed on on paved roads and trails only. Click here to download the map in PDF format. A hard copy of the map is available at the Nature Center in the park.
But, be aware of the small print. E-biking in Rock Creek Park on bicycle trails is allowed only if you pedal to propel your e-bike and if the e-bike meets the following requirements:

Beach Drive in Rock Creek Park is closed to cars and other motorized traffic on the weekends between Military Road and Broad Branch Road. The wide open and flat road is ideal for e-biking, skating, running and walking.
Below is text from the Superintendent's Compendium or Record of Determination, in case you want to read the text allowing e-bikes in Rock Creek Park.
Superintendent's Compendium or Record of Determination
2019
E-bikes are allowed in Rock Creek Park where traditional bicycles are allowed. E-bikes are prohibited where traditional bicycles are prohibited.
Except where use of motor vehicles by the public is allowed, using the electric motor continuously to move an e-bike without pedaling is prohibited.
An e-bike is a two- or three-wheeled cycle with fully operable pedals and an electric motor of less than not more than 750 watts (1 h.p.) that provides propulsion assistance.
Amended per the October 2, 2020 and November 2, 2020 updates. It is to expected that the 2020 compendium will include amendments pertaining class 2 E-bikes, made on November 2, 2020.

Peirce Barn in Rock Creek Park is the starting point for several of our e-biking trails. There is ample parking available on Tilden Street. Toilet blocks are located at Peirce Barn and the parking lot across the street from the barn.
One of the largest natural urban parks in the United States, this wooded preserve also contains a range of historic and recreational features in the midst of Washington, DC.
Authorized Sept. 27, 1890; transferred from Office of Public Buildings and Public Parks of the National Capital Aug. 10, 1933. Acreage—1,755.21, all Federal.
source: np Index

The iconic Boulder Bridge in Rock Creek Park was built in 1902. It carries Beach Drive. The bridge is constructed of concrete and faced with boulders. The largest boulders, up to 7 feet tall and weighing half a ton, are placed at the opening of the arch as voussoirs (wedge-shaped stones). Architects: U.S. Army Corps of Engineers and W.J. Douglas.
Spotlight
Some things you may not know about Rock Creek Park
Size
With just over 1,755 acres, Rock Creek Park is twice the size of Central Park in New York.
Planetarium
The only planetarium in the National Park System is located in the Nature Center of the park.
Shakespeare
A Shakespeare theatre production ran in the park's Carter Barron Amphitheatre from 1991 to 2009.
History
In 1890, Rock Creek Park was the third national park to be designated by the federal government.
Conclusion
Most e-bikes sold in the US have a motor of less than 750 watts, operate with functional pedals and have two wheels. Unless regulations change, e-biking in Rock Creek Park is permissible if you meet the requirements as stated above.
Note: If you buy an e-bike conversion set, ensure that the motor is not more than 750 watts to gain access to NPS trails when permitted by the superintendent of the park.
Interested in E-biking in Rock Creek Park ?
Explore our growing collection of self-guided e-biking trail descriptions.
As usual, please check the latest regulations before heading out as we do not provide legal advice on this website.
References
https://www.nps.gov/aboutus/upload/NPIndex2012-2016.pdf
DISTRICT OF COLUMBIA INVENTORY OF HISTORIC SITES ALPHABETICAL VERSION. (2009). [online] Available at: https://planning.dc.gov/sites/default/files/dc/sites/op/publication/attachments/Inventory%202009%200%20Alpha%20Version%2003%2011.pdf [Accessed 12 Jan. 2021].
https://www.nps.gov/rocr/learn/management/rock-creek-park-superintendent-compendium.htm [Accessed 15 Dec. 2020]
Sellers, F. (2014). Seven things you didn’t know about Rock Creek Park. [online] Washington Post. Available at: https://www.washingtonpost.com/news/arts-and-entertainment/wp/2014/07/16/seven-things-you-didnt-know-about-rock-creek-park/ [Accessed 12 Jan. 2021].
Nps.gov. (2020). Electric Bicycles (e-bikes) in National Parks - Biking (U.S. National Park Service). [online] Available at: https://www.nps.gov/subjects/biking/e-bikes.htm [Accessed 3 Sep. 2020]
Nps.gov. (2020). Electric Bicycles (e-bikes) in National Parks - Biking (U.S. National Park Service). [online] Available at: https://www.nps.gov/subjects/biking/e-bikes.htm [Accessed 14 Dec. 2020].
NATIONAL REGISTER OF HISTORIC PLACES INVENTORY -NOMINATION FORM FOR FEDERAL PROPERTIES. (n.d.). [online] Available at: https://npgallery.nps.gov/NRHP/GetAsset/a488f8c3-0618-474f-a796-da2d1eced1c7/ [Accessed 12 Jan. 2021].

Gregory discovered e-biking after 20 years of overseas work as project manager for the World Bank and USAID. He writes about e-mobility and e-biking in the DMV area, and loves the outdoors (white water kayaking, hiking and biking). He lives with his wife, Janet and Queenie the cat, in Washington DC. He recently e-biked 4,685+ miles across America and raised $180,000 for a charity.
Favorite e-bike: Riese & Muller Super Charger Class 3 touring e-bike.
Dr. Gregory F. Maassen
FOUNDER E-BIKE LOVERS