Answer: Interestingly, I had a hard time finding any info on this subject--a problem that must be fairly common. (It sounds like a good subject for a magazine article.)
Here are a few ideas:
You can create a flower bed, and grow annual flowers along the roadside. Nasturtiums, for example, thrive in hot, dry, relatively infertile sites. You'd need to start with new seeds or plants each year.
You might try a few exceptionally durable perennials, such as yarrow, gallardia, and sedum. Also Roman chamomile (Chamaemelum nobile) and evergreen candytuft (Iberis sempervirens)
You might contact the Brooklyn Botanic Garden, and ask about their research into salt-tolerant grasses, especially 'Salty' alkaligrass. Ask for a copy of the article from their publication BBG Plants, Spring 1997.
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