I can empathize with your wish to save the tree, but I would question whether it in fact should be saved, or even can be saved. It is too close to the road, and even if you could make it thrive, when it's bigger it will likely start to be hit by passing trucks, and the city might send out their mandatory tree hit squad to trim it back, which likely will be a recurring problem.

I can't tell quite what type of tree it is, but I'd bet it's having trouble either due to dirty water from the road (salt and grime) or too much heat hurting the roots, from the surrounding pavement in the Summer.

I might be a heretic, but not every tree should be kept. Many were planted in the wrong place, and in the wrong environment, and that's not your fault. How about planting two nice trees in nice places in your yard instead?

Just my thoughts...

Best of luck.

The odd thing is that the entire development has trees in similar places, yet my tree is the one that looks like this. Part of me wonders if there simply isn't enough soil in that particular spot.

OK, the first thing I would suggest is a ring of mulch around that tree (at least 2 ft in diameter) for moisture retention & as a mower buffer. It's perposterous to think the tree doesn't have enough "room" to grow....I mean really, the roots are growing & working BELOW the street & sidewalk. Mulch around it & make sure you keep it watered on a regular basis & I bet it does well...

Not that this helps much, but it appears to be a Black Walnut.

It looks like an ash. And you're going to want to look up Emerald Ash Borer.

Actually, what's preposterous is thinking that tree can be made viable in the long-term. People from North Carolina might not realize it, but it snows in NJ, which means road salt, I suspect, and snow plows. All that salty runoff is going right into that tree's roots. Also, it already appears that the branches over the road have been clipped off, either by the city or by trucks (ask anyone who's ever driven a big moving van). And I'm not sure how you could get a two foot mulch ring around it when it looks to be about eight inches from the curb.

I understand that there might be other trees on the street in the same situation that might be thriving, but every tree is different.

looks like an ash. I agree with philes21. I hope it's not the emerald ash borer.

I know trees are expensive and generally take forever to establish, so you might not like my opinion. As a general rule, trees can't be "saved." Once you get significant die back, you just have to cut your losses - literally.

As for a particular diagnosis - I have no idea. I'm sure an arborist could tell you, but for the cost of a visit, you may as well buy a new tree.

Agree that this one may not be saved. I'd talk with an arborist in your area.