If you are departing DCA Northwest, and are on an IFR flight plan, you must intercept the 328 radial and track it outbound. If doesn't matter if it's clear and a million, the procedure is labeled VFR and IFR....not VMC and IMC. I don't know of anyone leaving DCA on a VFR flight plan, so the 328 radial is it.
I will also share this tidbit with you, after having been shown radar plottings of our departure path with speed and altitude data, and the P56 A and B airspace on it.....no one has a chart with the airspace shown TO SCALE...look at the diagrams we have..nothing is to scale......P56B isn't a tiny little dot..it extends almost to the river.
I have never heard the tower in DCA tell anyone to hug the eastern edge of the river during River Visual 19 approaches, and would highly recommend against that procedure, but if you want to try it be my guest.
They are deadly serious about enforcing the Prohibited airspace in DCA...they will come after you if the cockpit is filled with smoke and you are on fire and breach it after losing both engines and the apu....I asked our FAA POI (who sat in the ASAP event review) about the above scenario, and he stated the no matter what the reason, violating it will result in an enforcement action.
I now get practice flying 1/2 dot west of the LDA DME 19 final approach course, and 1/2 dot west of the 328 radial. I'm sure someone will get on here and say that's unnecessary, but having been the target of one of these enforcements for P56B (naval observatory where the VP is supposed to reside but currently doesn't) a couple years ago, I'm gonna err on the side of caution, and the people in the USA today building and Rosslyn can be thankful it's a quiet jet.