How do I increase spacing between shields on the same road?


In Mapnik reference I find this:

The spacing between repeated occurrences of the same shield on a line
Default: none

In the xml file spacing are currently used like this within the ShieldSymbolizer tag:

<ShieldSymbolizer spacing="750"

I have tried to set it to 1500, and 0 - but none of these numbers make any difference in the spacing.

So how do I increase the space between shields on the same road?

Now shields are repating themselves to often, making the map interface cluttered with shields.

Using Mapnik 2.2, on Windows 7.

Here I have made the shields smaller both in width and height, applied a white background for all shields not a motorway, and shrinked the font as well. This helped a lot (compared to default look ref. Mapnik 2.2 XML, but it would be a lot better without shields repeating itself so often. Example is from level 11: