Class A = Excellent - suspiciously light or fast-moving traffic.
Class B = Better than normal - short queues or moving traffic.
Class C = Usual - queue lengths or traffic speed are as expected.
Class D = Bad - queues longer, progress slower than usual.
Class E = Terrible - enormous queues, excruciatingly slow progress.
Class F = Transport Failure - not moving at all.
Class E traffic makes it as quick, or quicker, to walk. Class F traffic makes it reasonable to abandon your journey.
