A decade sounds like a pretty good start. If we could combine that with transitioning away from lawns and towards gardens / orchards (like even on highway medians!), imagine the savings in terms of shipping food.
Seems like you'd intentionally plant many small/short trees that will act as nice crash barriers, not large strong trees that act like brick walls. Orchards tend to be short trees anyway.
Hitting the tree equivalent of those sand-filled barrels sounds a lot better than dissipating that same energy by either A) flipping, or B) colliding with oncoming traffic.
It would be interesting to see the videos of "crash testing" various types of orchards!
Grass contains even less carbon, and it doesn't produce anything of economic value.
As I wrote elsewhere in the thread, it's all about maximizing the total carbon stored per hectare. That means more trees in the median, more trees in our suburbs, more trees in the city, and (most importantly) more trees in agriculture.
There's a small set of "farmer's trees" (eg black locust) that coexist with crops right up to the trunk, drop copious mulch, have deep tap roots that bring up minerals, and make nutritious pods that are good fodder for animals. Planting 15-20 of these trees per hectare will actually increase the crop yield beneath.
Tons more carbon stored, better crop yield, cuts down wind erosion, and free fodder too. The cost is that the farmer has to drive around the trees. It's a non-zero cost yes, but it's a much easier switch than transitioning to full-on agroforestry.
