That's an interesting question. Its date of construction probably goes back to the electrification of 1906. The first phase of the Harlem Division electrification was completed that year and extended just about to E.241st Street at Wakefield. A photo in an old Railway Age showed the motor storage tracks (at the temporary engine change point) deadended at the New Haven flyover. Total grade crossing elimination was part of the electric project so presumably -- if E.241st once upon a time crossed the Harlem at grade -- it was closed at that time or a little later.
Was that when the bridge was built?
The bridge appears in photos at least from the 1920s I think. The thing I wonder about is, did New York Central really pay for it? New York City paid for a lot of the grade crossing elimination when Central was electrifying. In fact that's what held up the extension of the electric zone to North White Plains and Harmon. The County of Westchester would not pay for the grade crossing elimination and Central would not extend third rail without it. I think eventually they agreed to split the cost 50/50 between the county and the railroad.
I used to walk that bridge all the time back in the 1980s. I believe the 241st Street bridge crosses (from east to west) some city land, then (what was) the New Haven Railroad, a sliver of private property, then (what was) New York Central, then the Bronx River and, finally the Bronx River Parkway, though the Parkway probably came after the bridge. So the bridge crosses a lot more than just the Harlem tracks so maybe Central would not have been responsible for all the cost. Maybe NYC and the NH shared the cost? With maybe the City kicking in too?
Maybe it was just the railroads that paid. Because, I believe, when the viaduct was rebuilt about 15 years ago, Metro-North did get stuck with the repair bill. I think I read that in a Metro-North Milepost.
I guess all of which is a longwinded way of saying I don't know when the 241st Viaduct was built.