I did Highwood for the first and only time last year. I was out of shape and slow as hell compared to the guy I rode with. I think he was about 30 minutes faster than me. It's a good challenge and I want to do it again this year.
Here's my ride if anyone is interested in the data.
https://www.strava.com/activities/607469415
I did the South side. Here's the segment:
https://www.strava.com/segments/703006 (300/436 for me

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When does it open to cars?