we find that block groups that installed protected bicycle lanes experienced bicycle commuter increases 1.8 times larger than standard bicycle lane block groups, 1.6 times larger than shared-lane marking block groups and 4.3 times larger than block groups that did not install bicycle facilities. Focusing on mileage, protected bicycle lane mileage installed was significantly associated with bicycle commuter increases 52.5% stronger than standard bicycle lane mileage and 281.2% stronger than shared-lane marking mileage.

The answer to your question hinges on how gradular a “block group” is. It’s probably that safe infrastructure encourages biking.