I’m a regular user of the First Avenue bike lane in Manhattan and I love it. It’s by no means perfect — there’s still too much pedestrian dodging required in the East Village and Upper East Side — but it’s a huge step towards a safer and better use of that very wide avenue.
These days, my favorite stretch of the lane is the segment in front of the United Nations. The urban planner in me just loves how the bike lane merges beautifully with the vehicular lanes on the south end of the First Avenue tunnel, taking you comfortably past an area that used to be tricky for cycling. As an added bonus, there’s also now a Citi Bike station directly across the street from the Secretariat Building.
The only improvement I can think of would be giving one lane of the tunnel to bikes if cycle traffic one day warrants it. I’d love to see that in my lifetime.