In 2008 DDOT completed work on stairs from the New York Avenue Metro Station section of the Metropolitan Branch Trail to L Street NE, a trail in the L Street underpass beneath the railroad tracks and a one block portion of the trail along 2nd Street NE. The section of trail beneath the underpass was intended to be the city's first cycletrack (albeit a short one) with one section, closer to the road, for cyclists and a sidewalk closer to the wall. They even used different colors of concrete to differentiate which area was to be which.
Of course things didn't work out that way and the trail has remained unchanged here since 2008.
The NoMa BID is holding a contest to improve the underpasses in the area, which are currently dark and a little foreboding, and most of the designs for the L Street Underpass move away from this design. Several of the proposals add poles or hanging art that would get in the way of cyclists or divert trail users and seem to abandon the idea that the trail even utilizes the sidewal (although the one from Narduli doesn't).
While it's a good goal to see about improving these underpasses from an aesthetic standpoint, some of these improvements seem to come at the expense of the trail/transportation design rather than embracing them. DDOT should step in and make sure that the trail design elements they added in 2008 are not only protected, but enhanced. Perhaps it's time to more definitely partition the underpass for cyclists and pedestrians.