First check to see if your municipality regulates this activity. Seattle, for instance, has height restrictions and other rules.

I would be planting the islands for the village. I need plant options to present them in my proposal. Height limitation is about 36 inches, so as not to obstruct the view of drivers.

The city of Chicago has successfully populated many a median strip with the following plants:

At the top of the list: Prairie Dropseed - Sporobolus heterolepsis

New England Aster 'Purple Dome' - Aster Novae-anglae
Prairie Sundrops - Oenothera fruticosa
Wild Petunia - Ruellia humilis
Nodding Onion - Allium cernuum
Orange Coneflower - Rudbeckia fulgida (note: you want the straight species as the cultivar 'goldstrum' is prone to botrytis and should be avoided)

Traffic medians around here go with yuccas, short ornamental grasses, stella d'oro daylilies, russian sage (you'd need one of the short varieties), black-eyed susans, sometimes knock-out roses.

Some things that come to mind are:

Function: are they for shade, screening, iconic, aesthetic, pedestrian control, vehicular navigation icon, drainage control, erosion control?

Safety: consider sight lines, physical nature of the plant, proximity to other activities and people, concealing bad actors.

Structural Durability: woody plants break when loaded or impacted, grasses and herbaceous perenials rejuvenate, what is present if there is a snow load.

Situational durability: polution, dog visits, compaction of soil, wind, light, road salt

Maintenance: water, fert, size, shape, catching trash, removing debris.

When you get through defining the criteria, plant selection should be a good attempt to address those equitably based on how you weight those values.

coreopsis early sunrise. Blooms forever, likes dry and short. Hardy and attracts butterflies, which people like too.