If you are walking or cycling around Bangkok at night you really need to be careful of broken manhole covers. Some are on the road while others are on the sidewalk. This was my greatest worry during the floods falling down one of these holes. On my Soi alone there is one concrete manhole cover that is broken and three others with metal sheet covers that look like they will give way very soon. I always cycle around them just in case. The problem is heavy trucks on the roads and motorcycles on the sidewalk. Or is it inferior construction material?