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The connectivity index measures how many choices a cyclist has for turning from one bike route onto another without leaving the network. A bigger index means a network that is more complete and more interconnected, not just longer.
Methodology: Bike facility segments are joined into a network wherever they share an endpoint. An intersection only counts when at least 3 distinct bike routes meet; dead ends, corners, and one segment simply continuing into the next offer no turn choice. Segments that run in nearly the same direction from an intersection (for example a lane on each side of a street) are treated as a single route. Each pair of routes that meet at an intersection, other than going straight through, contributes lanes × lanes / 2 turn movements where a one-way lane counts as 1 and a two-way route as 2, so a two-way route crossing a two-way route contributes 8 and a T-intersection of two-way routes contributes 4. Each year shows the network that was installed and not yet retired by December 31 of that year (the latest year is through the most recent data). Greenways include link segments. Tiers are cumulative: Greenway, then + Class I (protected), then + Class II (unprotected), then + Class III (shared) for all facilities. Intersections are counted only within the selected borough, so borough totals do not sum to the citywide total.