My guess would be that they wanted to be able to stretch a cable across, at need.
Next time I pass by there I’ll stop and get out and take some photos.
You can see that there isn’t much room for pedestrians on the bridge, so I’ll have to be quick and keep an eye out, but I’m curious about the outside as well as what those letters are.
So they’re preparing for the coming zombie apocalypse? Good on you, New Jersey!
If you zoom in on the near hole, you can see there’s brick on the outside as well. But that could still be just for looks.
ETA: What letters are people talking about? All I see are the letters “DP”, and no smaller letters.
The answer may be somewhere in the engineering section of NJDOT’s website.
Design Manual for Bridges and Structures
Here’sthe next small bridge downriver (skipping the turnpike).
The bridge style is completely different, but there’s a notch on either side right in the middle. It’s not a hole and it’s not right next to an expansion joint. But it looks like it could serve the same purpose.
My guess is that they are “drafting points” for firefighting. The stream below the bridge does not look too far down which would allow good pumping. The holes would aid in the placing of the suction hose.
I dunno. Too small to fit a body through, and the wall is short enough you don’t need a hole.
I don’t know nuthin’, and I’m sticking with it. 
I think we have a winner. Here’s a PDF from Hopewell township, NJ, that says
The sixth picture in the gallery at that last link shows a cutout in the middle of a bridge that looks functionally close to the ones in the OP’s bridge.
I agree that that must be the answer. The openings are probably at the height of the hose connector on a pumper fire truck.
They are obviously cutouts as one of the bricks above a cutout is suspended in the middle of it. A difficult bit of bricklaying without a course of bricks below it.
Hardly. They could just use a metal lintel. Look at how the line where the mortar would be even with the top of the hole is darker.
ETA: Here’s a page with some lintels. They could have used one like L11, at the bottom of the page.
Yeah. Bricks dont just ‘suspend’ like that on their own. Mortar isn’t actually very strongly adhesive.
Yeah, admittedly, I couldn’t think of any good reason why defensive features would be built in. Also, if they were embrasures, there would probably be more of them.