Humps on Hump Day

I ought to know what these are. They're on a bridge over the canal. I expect they're something to do with WW2, but they don't have doors which I think rules them out as Pill Boxes. Or, of course, they might just be an elaborate device to deter parking.

I've been catching up on assignment work. I am slowly bending Photoshop to my will but it's hard work. Today I got a mask to do exactly what I wanted. I'm pretty sure I could remove the cable from this one but you know it's nearly bedtime...  Soon I will catch up on all your blips and comments, thank you for bearing with me during this slow patch.