The local council has a fleet of cargo carrying bicycles which are used by people doing work such as keeping the beaches and other areas of the city clean. They're painted with just the same colour-scheme as the vans, and the same scheme as the council's normal bikes. Typically for a job requiring a few workers these bakfietsen are outnumbered by the "normal" council bikes.
And underneath, here's another one in the city centre (with a standard council bike on the left and a "civilian" bakfiets in the background).
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