did you know that several streets on the Howard University campus are private streets ?

See this 12-15-2014 message:

You might post this as a response to the person who questioned walking their dog on Howard premises:

Several of the streets within Howard University were closed pursuant to a street closing bill enacted by the city council. They would, in effect, become private streets, so while the stretch you mentioned isn't specifically cited, it's probably not worth it to push the point. http://www.dcwatch.com/archives/council12/12-307.htm. 

Here is a piece from the above DC Watch link:

Chairperson Linda W. Cropp, at the request of the Mayor, introduced the following legislation which was referred to the Committed [sic] on _________.

To order the legal closing of Girard Street, Fairmont Street, and Howard Place, between Georgia Avenue and 6th Street N.W.; Sixth Street N.W., between Girard Street and Bryant Street; College Street from 6th Street to one block east of Fourth Street; and public alleys in Squares 3057, 3058 and 3064 in Northwest Washington, D.C. in Ward 1.

BE IT ENACTED BY THE COUNCIL OF THE DISTRICT OF COLUMBIA, That this act be cited as the "Closing of Girard Street, Fairmont Street, and Howard Place, between Georgia Avenue and 6th Street N.W.; Sixth Street N.W., between Girard Street and Bryant Street; College Street from 6th Street to one block east of Fourth Street; and public alleys in Squares 3057, 3058 and 3064, S.O. 94-213, Act of 1997."