median strip
US /ˈmiː.di.ən ˌstrɪp/
UK /ˈmiː.di.ən ˌstrɪp/

1.
a strip of land or concrete in the middle of a divided highway or road, separating traffic flowing in opposite directions
:
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The car swerved across the median strip into oncoming traffic.
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Trees were planted along the median strip to enhance the scenery.