Early Warning Method and Model of Inland Ship Collision Risk Based on Coordinated Collision-Avoidance Actions

Table 2

Comparison of two types of early warning methods.

	Early stage	Early warning conclusion	Later stage	Early warning conclusion	Early warning effectiveness
Group A	DCPA ≤ MinDCPA and TCPA > MinTCPA	A collision risk exists, but is not imminent	DCPA ≤ MinDCPA and 0 < TCPA ≤ MinTCPA	Imminent risk of collision exists	Ultimately, seven groups encountered close-quarters situations, and one was almost in immediate danger.
Group B	DCPA ≤ MinDCPA TCPA > MinTCPA, Co∈[1, Co1]	A collision risk exists, but is not imminent; an alert is issued that the two ships have not yet understood each other’s movements			Through step-by-step early warning alerts, when TCPA > MinTCPA, the vessels have understood each other’s movements and unified their avoidance strategies. Ultimately one group was almost in a close-quarters situation, but none encountered immediate danger
	DCPA ≤ MinDCPA TCPA > MinTCPA, Co∈[Co1, Co2)	A collision risk exists, but is not imminent; the vessels have understood each other’s movements; an alert is issued that the vessels have not unified their collision-avoidance strategies
	DCPA ≤ MinDCPA TCPA > MinTCPA, Co∈[Co2, Co3)	A collision risk exists, but it is not imminent; the vessels have unified their collision-avoidance strategies; an alert is issued that the vessels have not yet taken coordinated maneuvering actions
			DCPA ≤ MinDCPA 0 < TCPA ≤ MinTCPA, Co∈[Co3, e]	The collision risk is imminent; the vessels have taken coordinated maneuvering actions; an alert is issued that the vessels have to verify the effectiveness of collision-avoidance actions