That, and the heat from the road dries things out faster.

Keep adding the compost, it'll help hold moisture, but you'll also have to irrigate that area more than others.

Agreed. Streets and concrete curbing holds daytime heat into the night. That heat dries out the soil long after the sun goes down. I have run a soaker hose around adjacent to my driveway to help keep it moist. Which reminds me I need to turn that back on.

What I do is a very slow soak for several days. By slow I mean I set the water to trickle out of the faucet at 1 cup per minute. That's pretty slow when you spread it out over a 50-foot soaker hose. But it works when you leave it on long enough. Three days is usually enough in my soil. You'll have to come up with something for your particular situation.

It's the salt. My post is not going to be very helpful as a long time ago I was in a seeed store and asked what some bags of ? were for and the owner said it was an amendment for clay soils but he said he was selling tons of it that summer as people found it did wonders to conteract the salt in there tree lawns. Unfortunately I can't remember what it was so maybe someone here can put it together for you.

Granulated gypsum. Spread like lime.