While extra casings for bridges add visual clutter, it was noted by Minh in Slack that without them it can be difficult or impossible to disambiguate between an intersection and a flyover.

If we'd like to keep bridges subtle, then maybe just a slight extra width to the casing could be added. We could potentially layer two levels of casing (widest dark bottom, then a lighter slightly narrower, both under the normal road casing) to visually offset an outer bridge line from the normal casing. This technique could be especially useful for the dark-stroke style at lower zooms.

Maybe something along these lines:

This sort of treatment could work with both case+fill style as well as stroked style and shouldn't conflict with expressway rendering.

At some point features will become too small to make differentiating bridges useful, maybe somewhere around z12