There are different types of gaps explained here that can apply to transportation infrastructure:
System gaps: Larger geographic areas (e.g. neighborhood or business district) where road connectivity is poor or doesn’t exist.
Corridor gaps: On clearly defined or otherwise well-connected routes, corridor gaps are usually missing bicycle or pedestrian infrastructure links. These gaps will sometimes encompass an entire corridor where facilities are desired but do not currently exist.
Intersection gaps: Point-specific locations lacking dedicated facilities or other treatments to accommodate safe and comfortable pedestrian or bicycle travel. Intersection gaps primarily include areas with potential conflicts between vulnerable users and motor vehicles.
Redundancy: Includes developing a parallel roadway to handle capacity issues in an otherwise well-connected roadway network.