When first built, users of the bridge had to pay a half-penny toll, although this was withdrawn in 1895.
According to the ICE's Civil Engineering Heritage book, the bridge was widened in 1902, to cantilever the footpaths beyond the edge of the brickwork; and then the widening was "improved" in 1985, adding prestressed concrete beams on cantilevers to support both footways and new crash barriers.
Clearly, "improved" is used only in a technical sense, as the widening has utterly spoiled the appearance of the bridge. The original bridge appears not to have been a great beauty - its tall piers taper slightly, which seems attractive, but the semi-elliptical arches look awkward.
Now, the stubby little concrete cantilevers look quite horrible, and the effect of the deck widening is to hide the crowns of the arches, "squashing" them unpleasantly.