How best to map lines based on multiple attributes?

Question

I need to plot lines onto a map to display road quality. I'm already using colours to distinguish between different road conditions, but I also need to display another factor - the survey origin.

There are only two different origins to display, but I'm not sure what's the best way to do this. Dashed lines with gaps are not appropriate as surveys can legitimately contain gaps.

My current approach is to display the two types as follows:

1. Solid colour lines for one of the survey types.
2. For the second type, use a dashed line, but with the gaps drawn in a lighter shade of the same colour (shown below).

However it still seems a little confusing to see where surveys start and end.

Are there any alternatives or best practices to follow?

Answer 1

Since you are already symbolizing by road condition (which I'm guessing may be represented by a few colors), I would suggest to not use a multi color dash line to represent survey origin (sometimes less is more). I generally use a buffer/fade effect for displaying multi attribute line info, see caption below.