Originally Posted by livedarklions

Sorry, but if you've ever encountered one of these where the color of the metal matches the color of the pavement, they are not at all obvious. As I said above, many decades ago, I caught my wheel on one of these where the city had actually installed the grate the wrong way (it was square, and the other ones on the block were installed perpendicular to the street--i.e., correctly). Fortunately, I was not hurt and my bike was undamaged, but I don't think it's fair to call me clueless when the grate, the street and the spaces between the slats all appear black--it's really hard to see let alone measure. Also, keep in mind that these are most likely to be encountered in cities/suburbs where the traffic ahead of you is actually passing over the street feature when you'd be in a position to spot it.

I try to avoid riding over grates and manhole covers generally, but it's not always possible to avoid, especially in traffic.