A unique roadworthy boom trailer comprises a roadworthy wheeled chassis, four independently-adjustable trailer-leveling motorized legs attached to the bottom of the chassis, pneumatic-tool compressor built in the chassis, turret assembly attached to the top of the chassis, and on-site-extendable-interchangeable quick-release assemblies of boom, ladder, and catwalk rotatably attached to the turret assembly. The ladder assembly has safety rungs for safety cables to be hooked thereon. The catwalk assembly has adjustable telescopic safety handrails. The unique roadworthy boom trailer can work with suspension-cable-or-truss-type bridges, low-or-high-power-line bridges, short-or-tall-supporting-column bridges, single-or-multiple-lane bridges, and regular-or-rail-road bridges. The catwalk assembly can have multiple additional catwalk assemblies attached thereto to extend its width or length to generally equal the width or length of a bridge, respectively. The catwalk assembly is sized to operate entirely within the width of a sidewalk, and to lift and shift equipment and personnel through narrow openings or into nooks both over and under bridges.