Season Speed Baseline

This is a descriptive route/corridor speed-norms comparison only — it does not resolve, support, or undermine the causal question of whether StationKeeper messaging reduces speed (that question was closed out separately via a difference-in-differences analysis; see the main investigation report). This asks a different question: what speed do the same shipping corridors, in the same direction of travel, naturally see when the NARW seasonal speed rule isn't even in effect — and how does that compare to ordinary in-season ambient traffic and to the vessels that actually got messaged?

40,550Out-of-season transits

37,241In-season ambient transits

9.3 ktMedian out-of-season

8.7 ktMedian in-season ambient

+0.6 ktPooled median difference

What it shows

Out-of-season traffic runs modestly faster than in-season ambient traffic in 7 of 9 corridors (+0.1 to +2.1 kt at the median) — Block Island Sound and Off Race Point are the exceptions, both at very low absolute speeds (median 2–8 kt), consistent with those boxes capturing slow near-port/anchorage traffic rather than open-corridor transit. Where the gap is real, it's modest — mostly under 2 kt — and the pooled in-season-ambient median (8.7 kt) already sits comfortably under the 10 kt NARW limit, meaning ordinary traffic isn't typically hugging the line regardless of the rule. Critically, the messaged incidents' own pre-trigger speeds (11–14 kt in most corridors) sit well above both seasonal baselines in 8 of 9 SMAs — these vessels are running faster than typical traffic on the same routes, not just experiencing an ordinary cruising speed that happened to become illegal. A secondary, modest signal: the same vessels show more speed variability out-of-season than in-season in 7 of 9 corridors (e.g. Chesapeake: within-vessel SOG std 1.98 out-of-season vs 0.92 in-season), suggesting the season/rule environment may narrow the speed distribution somewhat — though this reverses in one SMA and shouldn't be read as a clean verdict.

Comparison chart

In-season vs out-of-season speed comparison by SMA

Per-SMA detail

SMA	n in-season	n out-season	Median in (kt)	Median out (kt)	Δ median	Pre-trigger median (kt)	Within-vessel std, in	Within-vessel std, out
Delaware SMA	4224	4409	9.0	10.6	+1.6	11.15	1.05	2.55
Great South Channel	556	467	9.0	10.4	+1.4	12.3	0.49	1.1
Block Island Sound	4764	6257	3.1	2.0	-1.1	12.25	1.08	1.62
Chesapeake	8899	7188	9.1	10.0	+0.9	12.35	0.92	1.98
NY/NJ	8039	6846	8.9	9.5	+0.6	13.1	1.63	2.11
Mid-Atlantic (South)	5422	6420	9.0	11.1	+2.1	13.05	2.72	1.84
Cape Cod Bay	1085	2853	8.1	9.2	+1.1	9.28	1.7	2.5
Off Race Point	383	1622	8.0	7.8	-0.2	13.8	0.57	1.59
Southeast/Calving Grounds	3869	4488	8.9	9.0	+0.1	12.6	1.68	2.26

Example Out-of-Season Vessel Movements

108 example transits (12 per SMA, sampled across the low/mid/high speed terciles to show variety, not just the median case) — actual vessel paths through each corridor with no NARW speed rule in effect. Track colored green ≤10kt / yellow 10–12.1kt / red ≥12.1kt; ■ marks the transit's starting position; SMA boundary in magenta. Some corridors (Cape Cod Bay, Off Race Point) show tight crossing/looping patterns rather than clean transit lines — likely fishing or loitering traffic rather than through-traffic, worth keeping in mind when reading their speed stats.

Per-SMA grid of example out-of-season vessel tracks

Example Vessel List

Vessel	AIS type	MMSI	SMA	Date	Min (kt)	Max (kt)	Avg (kt)	Distance (nm)
BRANDY STATION	Other type	368803000	Delaware SMA	2026-09-01	0.0	9.5	1.0	13.2
CALUSA COAST	Tug	367029960	Delaware SMA	2026-06-14	4.1	7.2	5.1	18.6
ETERNITY	Passenger	367099280	Delaware SMA	2026-05-01	6.5	8.3	7.1	3.9
DEFENDER	Tug	368138460	Delaware SMA	2026-07-13	5.6	9.4	7.9	162.6
LA CONDAMINE	Tanker	228433700	Delaware SMA	2026-07-27	6.7	10.8	8.4	17.2
AS FELICIA	Cargo	255806103	Delaware SMA	2026-05-15	4.1	14.6	10.7	29.9
WICKY SPIRIT	Tanker	316041032	Delaware SMA	2026-07-24	8.1	11.2	11.0	19.8
MANTA NILGUN	Cargo	538009477	Delaware SMA	2026-08-21	7.6	12.9	12.2	19.2
MSC STAR R	Cargo	636015031	Delaware SMA	2026-06-22	8.3	13.9	12.6	18.8
NYMFAION LADY	Tanker	563164700	Delaware SMA	2026-07-20	9.8	15.1	13.4	19.1
R/V JOANNE DAIBER	Not available	338169577	Delaware SMA	2026-08-18	13.8	19.6	16.9	39.0
CG45665	Search and rescue vessel	369493665	Delaware SMA	2026-05-09	33.9	33.9	33.9	0.0
AVENGER	Fishing	367379150	Great South Channel	2026-03-10	0.0	6.1	2.6	25.4
MSC SINDY	Cargo	372736000	Great South Channel	2026-02-08	4.0	8.5	6.0	29.7
BBC FELIX	Cargo	255916062	Great South Channel	2026-01-17	7.9	11.5	9.3	25.5
MSC BERANGERE	Cargo	636021665	Great South Channel	2026-01-01	9.1	10.2	9.4	15.1
BULK ATACAMA	Cargo	636022964	Great South Channel	2026-03-11	9.2	9.5	9.4	13.5
INDEPENDENCE OTS	Passenger	309374000	Great South Channel	2026-09-04	9.8	9.9	9.9	1.1
ZIM EMERALD	Cargo	563291900	Great South Channel	2026-01-22	10.7	11.9	11.2	27.7
HAFNIA TIGER	Tanker	564230000	Great South Channel	2026-01-22	11.4	12.6	12.2	19.9
LUNITA	Cargo	257427000	Great South Channel	2026-01-04	12.1	12.5	12.4	10.7
HAFNIA DAISY	Tanker	249347000	Great South Channel	2026-01-25	13.2	13.9	13.5	14.1
ZIM CORAL	Cargo	563291700	Great South Channel	2026-03-31	9.3	16.1	15.2	18.9
CG45678	Search and rescue vessel	369493678	Great South Channel	2026-08-20	0.9	37.3	22.9	10.4
WIND SCYLLA	Cargo	356068000	Block Island Sound	2026-08-26	0.0	0.1	0.0	0.0
NANUQ	Wing in ground	338361000	Block Island Sound	2026-08-14	0.0	9.6	0.8	7.0
JO-ANN V	Fishing	368294050	Block Island Sound	2026-07-19	0.0	8.8	1.4	20.2
SEA WIND	Fishing	368364250	Block Island Sound	2026-07-30	0.7	4.0	2.7	33.3
ECO EDISON	Other type	368359690	Block Island Sound	2026-08-07	0.0	10.1	3.3	55.7
SOVEREIGN	Tug	205644000	Block Island Sound	2026-05-28	0.0	9.2	3.4	30.8
GENERATER	High speed craft	368379370	Block Island Sound	2026-06-08	0.0	9.9	5.3	66.5
ERICA KNIGHT	Fishing	338402566	Block Island Sound	2026-07-03	0.0	9.6	5.4	25.2
ATLANTIC PIONEER	High speed craft (HSC)	367722360	Block Island Sound	2026-05-27	0.0	24.4	6.1	18.1
NACC PROVIDENCE	Cargo	352001173	Block Island Sound	2026-07-24	5.9	6.7	6.4	33.4
ARGO B	Cargo	538003906	Block Island Sound	2026-05-28	10.2	11.2	10.9	34.1
Unknown	Sailing	338650608	Block Island Sound	2026-05-09	52.7	52.7	52.7	0.0
LIVING STONE	Other type	244010952	Chesapeake	2026-08-23	0.0	0.2	0.0	1.4
NEPTUN FURY	Tug	244514000	Chesapeake	2026-05-04	0.0	9.7	3.3	11.6
WARSHIP 95	Military ops	369962000	Chesapeake	2026-06-30	0.0	12.0	5.5	28.8
CHARYBDIS	Other type	338146000	Chesapeake	2026-09-05	3.0	10.0	6.8	23.2
HOS ROSEBUD	Cargo	368269610	Chesapeake	2026-07-17	9.2	10.4	10.0	18.5
GIA GLORY	Cargo	538009917	Chesapeake	2026-08-16	9.7	10.7	10.3	19.7
SMUGGLERS POINT	Fishing	367163370	Chesapeake	2026-08-14	11.1	12.7	12.1	11.2
HAMPTON ROADS	Pilot vessel	368042970	Chesapeake	2026-06-15	6.0	24.6	12.7	4.6
SANDERLING ACE	Cargo	538007573	Chesapeake	2026-06-18	10.1	16.8	12.7	19.2
GRANDE LAGOS	Cargo	247341100	Chesapeake	2026-08-28	8.5	14.7	12.9	19.9
SANTA LORETTA	Cargo	218643000	Chesapeake	2026-08-23	9.6	18.0	16.8	19.6
VBFD FIRE BOAT 12	Search and rescue vessel	338560912	Chesapeake	2026-08-28	4.5	39.6	34.7	3.6
ARCTIC STAR	Tanker	241952000	NY/NJ	2026-07-30	0.0	0.5	0.0	1.3
CAPTAIN DAVE III	Passenger	367610930	NY/NJ	2026-08-10	0.0	8.8	1.1	5.4
PRIDE OF BALTIMORE 2	Sailing	303615000	NY/NJ	2026-07-03	4.0	4.2	4.2	0.1
Unknown	Sailing	228796000	NY/NJ	2026-07-07	2.9	9.0	7.1	9.3
ONE AQUILA	Cargo	374858000	NY/NJ	2026-08-08	6.0	12.3	8.0	22.4
CHOPTANK	Towing	367147860	NY/NJ	2026-06-05	7.0	9.3	8.3	22.3
STI WESTMINSTER	Tanker	538005539	NY/NJ	2026-06-11	0.0	13.8	8.4	16.8
SFL MAUI	Cargo	636021013	NY/NJ	2026-05-25	6.4	11.2	8.9	20.5
MSC NOA	Cargo	636018659	NY/NJ	2026-06-25	8.0	10.1	9.1	22.6
PORT EVERGLADES EXPR	Cargo	563281200	NY/NJ	2026-07-04	5.0	17.6	13.3	22.2
ATLANTIC SEA	Cargo	215800000	NY/NJ	2026-06-26	8.3	14.7	13.4	23.6
FDNY M8A	Search and rescue vessel	368111610	NY/NJ	2026-07-31	0.1	36.0	25.7	17.1
MAERSK HARTFORD	Cargo	338403000	Mid-Atlantic (South)	2026-08-30	0.0	0.4	0.0	1.9
SPIEKEROOG	Cargo	305997000	Mid-Atlantic (South)	2026-04-30	0.0	0.5	0.2	0.8
BIG M CASINO	Passenger	366992110	Mid-Atlantic (South)	2026-06-14	2.8	13.8	8.2	53.1
Unknown	Unknown	241552170	Mid-Atlantic (South)	2026-07-30	8.3	8.3	8.3	0.0
TWIN COVE	Pleasure craft	368069720	Mid-Atlantic (South)	2026-05-19	6.7	10.4	9.0	54.1
NABELLA	Pleasure craft	338427981	Mid-Atlantic (South)	2026-04-28	4.4	16.0	10.0	9.9
SPRING ODYSSEY	Cargo	352006552	Mid-Atlantic (South)	2026-06-29	11.2	12.2	11.9	3.4
ALTAMIRA EXPRESS	Cargo	563277100	Mid-Atlantic (South)	2026-09-03	7.3	16.3	13.3	20.2
OOCL KAPOK	Cargo	477156100	Mid-Atlantic (South)	2026-05-18	10.8	16.7	13.8	18.9
CMA CGM GANGES	Cargo	256104000	Mid-Atlantic (South)	2026-08-28	0.0	17.6	14.1	86.6
ALLIANCE FAIRFAX	Cargo	366771000	Mid-Atlantic (South)	2026-07-07	10.0	15.4	14.3	1975.0
MS-CF-1	Law enforcement	338556454	Mid-Atlantic (South)	2026-07-01	40.7	43.0	41.9	3.0
CHECKMATE40	Pleasure craft	368460470	Cape Cod Bay	2026-06-25	0.0	0.0	0.0	4.8
JOY	Passenger	368086399	Cape Cod Bay	2026-08-21	0.0	10.1	1.9	24.3
CGC MAURICE JESTER	Law enforcement	338926452	Cape Cod Bay	2026-06-02	2.5	13.2	6.1	73.1
ROBERT GRAY	High speed craft	368158120	Cape Cod Bay	2026-07-16	7.1	10.1	8.3	185.5
SEA HAWK	Spare	366843420	Cape Cod Bay	2026-05-23	7.7	10.1	9.7	26.7
RV DISCOVERY	Other type	338522247	Cape Cod Bay	2026-06-25	0.2	16.8	10.6	71.6
DOLPHIN X	Not available	367487640	Cape Cod Bay	2026-05-22	0.0	23.9	10.8	37.0
TAILS OF THE SEA	Passenger	367450190	Cape Cod Bay	2026-06-13	0.0	25.4	12.7	216.1
ANJILIS	Pleasure craft	319072000	Cape Cod Bay	2026-08-10	10.7	13.5	13.0	26.5
PATIENCE	Pleasure craft	319844000	Cape Cod Bay	2026-07-18	10.0	13.8	13.0	45.3
CG29136	Search and rescue vessel	369990136	Cape Cod Bay	2026-05-21	0.0	42.2	24.4	10.9
PROVINCETOWN III	Passenger	366954420	Cape Cod Bay	2026-07-10	0.0	30.6	28.2	282.9
HURRICANE II	Other type	366859760	Off Race Point	2026-05-08	0.0	20.0	1.3	1.2
TAILS OF THE SEA	Passenger	367450190	Off Race Point	2026-08-10	0.3	13.9	3.8	0.8
CAPT JOHN & SON	Passenger	367450150	Off Race Point	2026-07-12	0.2	17.7	4.2	5.8
TAILS OF THE SEA	Passenger	367450190	Off Race Point	2026-06-20	0.1	20.4	6.0	11.5
CAPT JOHN & SON	Passenger	367450150	Off Race Point	2026-06-13	0.0	18.2	7.9	41.5
DENALI	Spare	367452180	Off Race Point	2026-08-23	8.1	8.7	8.4	11.2
CGC WILLIAM CHADWICK	Law enforcement	338926450	Off Race Point	2026-07-10	8.6	11.1	9.9	45.5
DAISY MAE	Not available	367797720	Off Race Point	2026-05-27	9.9	10.8	10.3	18.3
EVER FRANK	Cargo	563163400	Off Race Point	2026-06-29	8.5	15.1	11.5	86.8
PRIVATEER IV	Passenger	367529770	Off Race Point	2026-06-05	0.0	19.1	13.3	46.7
SANCTUARY	High speed craft	367677670	Off Race Point	2026-06-09	0.1	29.8	15.2	114.4
CG27102	Search and rescue vessel	338926622	Off Race Point	2026-06-05	30.1	37.3	34.4	1.2
UBC TILBURY	Cargo	212040000	Southeast/Calving Grounds	2026-07-05	0.0	0.9	0.2	1.1
SMITH PRIVATEER	Not available	367396520	Southeast/Calving Grounds	2026-07-12	0.0	8.0	2.2	45.3
PACIFIC DAWN	Towing	366847780	Southeast/Calving Grounds	2026-07-10	6.4	7.4	7.0	6.1
SAGA MONAL	Cargo	311001622	Southeast/Calving Grounds	2026-05-24	0.0	11.7	7.1	22.5
CALCASIEU RIVER	Port tender	367313850	Southeast/Calving Grounds	2026-08-10	0.0	22.7	8.0	61.4
HOEGH SEOUL	Cargo	257496000	Southeast/Calving Grounds	2026-05-01	4.7	11.6	8.6	27.8
NORDMOSEL	Cargo	255806294	Southeast/Calving Grounds	2026-08-01	4.3	12.9	10.4	27.2
LIBRA LEADER	Cargo	636022754	Southeast/Calving Grounds	2026-04-25	8.7	16.8	10.6	31.7
TITANIA	Cargo	248225000	Southeast/Calving Grounds	2026-04-21	5.1	14.1	11.4	28.2
ATB LIBERTY	Towing	369109000	Southeast/Calving Grounds	2026-08-15	10.1	12.8	11.7	36.0
US GOVT VESSEL 19	Military ops	368926297	Southeast/Calving Grounds	2026-08-20	9.8	15.2	11.7	5.6
USCG 33154	Military ops	369493454	Southeast/Calving Grounds	2026-08-14	38.1	41.6	39.7	24.6

Distance = total path length tracked that day within the SMA polygon, not straight-line displacement.