A simple but effective matrix visual built using Charticulator. The matrix comprises three categories; Accident Type, Road Type and Year. I used a gradient fill to show the values, and coloured borders to identify the Accident Type.
This chart uses both x- and y- categorical axes with a rectangle mark as the glyph. The top x-axis showing the Accident Type uses a text mark anchored to the glyph and using the Visibility attribute (and Conditioned by…) only shows for “70 mph”.
Hope this is interesting, I haven't found how to embed the pbix, but contact me if you would like a copy to play with.