Possible Clues:

• Caught by traffic light at bend in the road
• It's fossilised after a century on the road
• Convex shape of road surface
• Arch going across the road
• Slight convexity, as of the surface of a road
• Slight upward curve in road, wing etc
• Convex shape of a road surface
• At last, traffic light may appear on road
• After a century it's yellow enough to be up in the road
• Slight tilt