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What does a small square yellow sign with a red cross mean? I encountered this on the autobahn in , and it appeared directly before and after bridges. In addition, there was sometimes a similar sign with a white cross in the central reservation.

Street View example, red cross on yellow sign

(from Google Street View, location)

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These signs are, as some answers state, for snow plow operators to mark parts of the streets where the snow plow has to be lifted to prevent hooking into the surface and damaging the plow.

The crosses are placed on expansion gaps and other elevations in the road. There are also arrows which indicate to keep distance to the curb. Those are mostly placed on sewer grates and similar features on some side of the road.

As the snow plow usually moves relatively fast (above 50km/h) with a lot of downward force to scrape the ice from the surface, the damage while hooking into the street is colossal, not only destroying the plow, but also the truck.

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    You can easily see something in the road, right at the sign, and cut off by the left edge of the picture. This is the thing that the sign is warning about. Whatever it is will cause damage to the plow, and the plow will cause damage to the road.
    – FreeMan
    May 31, 2022 at 12:23
  • @FreeMan Beginning of a bridge ("Brücke" Z 24), probably one of the expansion gaps mentioned. Yes, indeed: Google streetview is here: google.com/maps/@47.1182836,13.5754352,3a,75y,278.74h,82.45t/… The funny construction to the right is a noise protection wall with a window so that motorists can have a view of the valley.
    – Peter - Reinstate Monica
    Jun 1, 2022 at 13:44
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In Switzerland, there are signs of the same size positioned at the beginning and end of bridges, overpasses, etc... along motorways and some secondary roads.

Likewise, there is no reference to them in driving education material, and they are different in each canton. In Valais and Bern cantons, they show the picture of a truck with a giant shovel or blade.

The commonality with Austria is the higher exposure to snowfalls, due to the geographic situation.

My guess about their usefulness would be: when the roads have to be cleared of snow in winter, the snowplow operators know when they are going to enter an overpass section. They may take extra caution not to push snow off the side that may fall on the other road below, and resume normal procedure after they leave the overpass section, marked by the second sign.

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    The bridge surface may freeze before other parts of the road, so different cold weather treatment may be needed as well as more care.
    – Weather Vane
    May 30, 2022 at 13:51
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    Bridges cool quicker than roads, as they also cool from the underside. Thus they need more aggressive de-icing. But at the same time they normally are made of (steel) reinforced concrete (or a steel box), which can't be de-iced with salt (this will cause rusting), so urea needs to be used.
    – CSM
    May 30, 2022 at 16:22
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    I would rather assume that the signs are at expansion joints, where the plow must be lifted to prevent damaging the joint or perhaps as an instruction to interrupt road salting, as salt water may seep into and destroy the concrete around such joints. Bridges must also be cleared for snow in winter, even if there is something under the bridge, as otherwise the snow may easily overload the bridge, so the sign is unlikely used to stop plowing the bridge completely. I just find it a little bit odd, that I have never seen any special markings on Norwegian roads.
    – Tor-Einar Jarnbjo
    May 30, 2022 at 17:04
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    @Tor-EinarJarnbjo Expansion joints would also be my guess. Searching around in the neighborhood using the link in the question shows that those signs are always precisely at the expansion joints, with a white on yellow counterpart on the inside of the road if that joint is not perpendicular to the road. If it was meant to mark the bridge instead, I would also expect a different sign at the other end of the bridge, instead it is again the same.
    – mlk
    May 30, 2022 at 19:33
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    The signs in Switzerland are red and green. The red one indeed indicates that snow plows are no longer allowed to shove snow to the side of the road because it would fall on other participants (pedestrians, cars, railway, ...). The green one allows plowing to the side again. I drive a lot and I have specifically spent time investigating each bridge I drive over if they have the symbol or not and it is extremely consistent. Whenever there is something besides nature below the bridge you have the symbol, otherwise not (or if there is a "wall" on the side of the bridge).
    – Yanick Salzmann
    May 30, 2022 at 19:37
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These signs are probably there for road maintenance crews, maybe to show where bridges begin and end. They aren't taught in driver's school in Austria.

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