They're too small to provide efficient intersection execution. I suspect they're there just for "traffic calming" to slow bike traffic as it approaches the intersection of various trails.

You can see two in this Youtube video at 1:04 and 1:12. The one at 1:04 has been removed.

Here is a still of the one I slipped off:


""Look! It's Grandpa!" and ran in for a hug." Priceless! My grand-daughter is 24 and married. Her husband is deployed overseas. She called me the office the other day and said she was having breakfast...oatmeal and coffee and reading the news..."just like you!" My heart is full.