The idea of roads that glow in the dark is one any kid (or kid-at-heart adult) can appreciate, as well as a possible boon to safety. But the pilot project in the Netherlands has run into a serious stumbling block: the roads go dark when they get too wet.

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More specifically, moisture, such as that encountered during rainfall, can quickly reduce the effectiveness of the glowing paint’s light output—the pilot road markings were just put in place two weeks ago, reports the BBC, and yet already they’re dimming due to large amounts of rain.

Another potential pitfall to the glowing lane markers: drivers have already been spotted cruising down the road in the test area with their headlights off so that they can see the glowing lines—a clear safety hazard if such roads should become widespread.

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Nevertheless, the engineering firm Heijmans, which is behind the realization of the pilot program in the Netherlands along with interactive artist Daan Roosegaarde, says a new version of the glowing road markings is already in development, and will be ready later this summer.

Presuming the second iteration of the glow-in-the-dark roads works as expected, a wider rollout is planned, both within the Netherlands and in other countries.