Hi Dave,
I use in my nuvi 1490 another img file with only arrows and bridges.
I don't know explain why, but with another img file all arrows and bridges are always on top of the way.
In styles i have only the line file, and I use one code for each type of way, because I use different colors for each arrow and bridge (the same of the darker color way)
highway=motorway & (oneway=yes | oneway=1 | oneway=true) [0x10401 resolution 24]
highway=trunk & (oneway=yes | oneway=1 | oneway=true) [0x10402 resolution 24]
highway=primary & (oneway=yes | oneway=1 | oneway=true) [0x10403 resolution 24]
highway=secondary & (oneway=yes | oneway=1 | oneway=true) [0x10404 resolution 24]
highway=tertiary & (oneway=yes | oneway=1 | oneway=true) [0x10405 resolution 24]
highway=minor & (oneway=yes | oneway=1 | oneway=true) [0x10406 resolution 24]
highway=living_street & (oneway=yes | oneway=1 | oneway=true) [0x10406 resolution 24]
highway=residential & (oneway=yes | oneway=1 | oneway=true) [0x10406 resolution 24]
highway=service & (oneway=yes | oneway=1 | oneway=true) [0x10407 resolution 24]
highway=bridleway & (oneway=yes | oneway=1 | oneway=true) [0x10407 resolution 24]
The result is something like that

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I'm testing different colors and kinds of arrows too.
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Wesley