Types of Traffic Counts and Their Applications
CVC, TMC, spot speed, and OD surveys explained — what each measures and when to use it.
Different planning and enforcement questions call for genuinely different count types — using the wrong one doesn’t just give incomplete data, it can give data that actively misleads a downstream decision.
Classified Volume Count (CVC) answers “how much traffic, and what kind, passes this point” — vehicle counts broken down by type, typically in 15-minute intervals. This is the foundation dataset for road capacity assessment and pavement design, since vehicle-class mix directly affects design loading.
Turning Movement Count (TMC) answers “how does traffic actually move through this junction” — every movement (straight, left, right) by approach and vehicle class, all approaches simultaneously. This is the core input for signal-timing design and junction capacity analysis.
Spot speed studies answer “how fast is traffic actually moving at this point” — a speed distribution across the traffic stream, from which the 85th-percentile speed becomes the engineering basis for setting speed limits.
Origin-Destination (OD) surveys answer “where does this traffic actually come from and go to” — trip-pattern data that’s foundational for corridor planning and understanding whether a proposed intervention (bypass, new route, closure) will divert traffic the way planners expect.
Each has a distinct methodology, a distinct data output, and a distinct downstream use — picking the right one starts with being precise about which question actually needs answering.
