Freight shipment modal split and its environmental impacts: An exploratory study

Figures & data

Figure 1. Framework of an integrated freight emission project.

Figure 2. Maps of freight zones (adapted from Federal Highway Administration, U.S. Department of Transportation [2011] and Research and Innovative Technology Administration, U.S. Department of Transportation [2011]): (a) FAF³ analysis zones and (b) national transportation analysis regions (1993 CFS).

Table 1. Data statistics by mode and commodity type (4 years total)

(a) Commodity type	(b) Commodity description	(c) Number of observations	(d) Truck		(e) Rail
			tons (thousands)	%	tons (thousands)	%
1	Agricultural products and fish	5,704	4,585,159	12.63	530,930	9.52
2	Grain, alcohol, and tobacco products	8,202	2,485,347	6.84	158,335	2.84
3	Stones, nonmetallic minerals, and metallic ores	5,630	7,830,644	21.56	550,560	9.87
4	Coal and petroleum products	4,657	5,339,089	14.70	2,999,961	53.76
5	Basic chemicals, chemical and pharmaceutical products	8,824	1,928,319	5.31	585,510	10.49
6	Logs, wood products, and textile and leather	9,102	3,197,305	8.80	261,422	4.69
7	Base metal and machinery	9,053	6,377,410	17.56	291,342	5.22
8	Electronic, motorized vehicles, and precision instruments	7,651	597,028	1.64	51,440	0.92
9	Furniture, mixed freight, and miscellaneous manufactured products	7,561	3,326,713	9.16	145,849	2.61
10	Commodity unknown	3,093	649,901	1.79	4,428	0.08
	Total	69,477	36,316,916	100.00	5,579,778	100.00

Figure 3. Total tonnage and freight value per ton in 4 years: (a) total freight tonnage increasing rate and (b) freight value per ton.

Figure 4. Cumulative percentage of (a) total tons and (b) ton-miles shipped.

Table 2. Estimation results and goodness of fit

			Type 1	Type 2	Type 3	Type 4	Type 5	Type 6	Type 7	Type 8	Type 9	Type 10
(a) Estimation results	Intercept	Estimate	1.902E+00	1.163E+00	3.116E+00	−1.025E+00	4.035E−01	2.570E+00	3.305E+00	1.654E+00	3.131E+00	1.000E+00
		z-Statistic	18,886.00	4,133.00	43,384.00	−12,938.00	3,623.00	22,229.00	27,944.00	4,071.00	19,169.00	712.30
		Pr(>|z|)	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
	Value per ton	Estimate	2.379E−03	1.913E−03	1.100E−03	1.199E−02	7.781E−04	4.285E−04	1.627E−04	1.580E−04	2.977E−04	4.413E−03
		z-Statistic	8,939.00	7,237.00	1,414.00	29,956.00	10,033.00	4,201.00	1,880.00	2,672.00	2,053.00	2,833.20
		Pr(>|z|)	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
	Average truck distance × WTI crude oil price	Estimate	−4.681E−05	−2.748E−05	−6.435E−05	−5.718E−05	−1.812E−05	−3.392E−05	−2.858E−05	−1.547E−05	−2.059E−05	−3.941E−05
		z-Statistic	−16,435.00	−8,868.00	−11,929.00	−17,077.00	−8,360.00	−10,774.00	−8,523.00	−3,534.00	−4,569.00	−1,153.80
		Pr(>|z|)	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
(b) Number of data used			3,803	5,468	3,753	3,105	5,883	6,068	6,036	5,101	5,041	2,062
(c) Pseudo	McFadden		0.305	0.316	0.171	0.665	0.256	0.241	0.121	0.127	0.044	0.332
R ^2	Nagelkerke		0.348	0.344	0.187	0.764	0.300	0.262	0.129	0.143	0.047	0.338

Table 3. Comparison between observed and predicted total truck shares and paired comparison

	(a) Number of data used	Total truck shipment share (%)			Paired comparison (α = 0.05)
		(b) Observed	(c) Predicted	(d) = |(b) − (c)|	(e) p-Value	(f) Test result
Type 1	1,901	89.306	89.997	0.691	0.6490	Do not reject H0
Type 2	2,734	94.147	94.245	0.097	0.8436	Do not reject H0
Type 3	1,877	92.013	94.410	2.397	0.3013	Do not reject H0
Type 4	1,552	68.086	69.409	1.322	0.4658	Do not reject H0
Type 5	2,941	77.928	77.328	0.600	0.6329	Do not reject H0
Type 6	3,034	92.568	92.274	0.294	0.7060	Do not reject H0
Type 7	3,017	94.879	96.077	1.198	0.5125	Do not reject H0
Type 8	2,550	92.403	91.158	1.246	0.3011	Do not reject H0
Type 9	2,520	94.223	96.442	2.219	0.2052	Do not reject H0
Type 10	1,031	99.363	99.497	0.134	0.6305	Do not reject H0

Figure 5. Observed and predicted truck shipment shares for (a) type 6 and (b) type 8 commodities.

Figure A1. Observed and predicted truck shipment shares for all commodity types: (a) commodity type 1, (b) commodity type 2, (c) commodity type 3, (d) commodity type 4, (e) commodity type 5, (f) commodity type 6, (g) commodity type 7, (h) commodity type 8, (i) commodity type 9, and (j) commodity type 10.

Table 4. Modal split and emission estimations under different WTI crude oil prices

(a) WTI crude oil price ($/barrel)	(b) Truck share prediction (%)	(c) Rail share prediction (%)	(d) Truck CO2 emission (ton)	(e) Rail CO2 emission (ton)	(f) Total CO2 emission (ton)	(g) Truck CH4 emission (kg)	(h) Rail CH4 emission (kg)	(i) Total CH4 emission (kg)	(j) Truck N2O emission (kg)	(k) Rail N2O emission (kg)	(l) Total N2O emission (kg)	(m) Truck PM10 emission (kg)	(n) Rail PM10 emission (kg)	(o) Total PM10 emission (kg)
50	68	32	66,247	3,560	69,807	781	283	1,063	602	85	687	20,521	1,836	22,358
60	64	36	62,228	4,012	66,240	733	318	1,052	566	96	661	19,276	2,070	21,346
70	59	41	58,006	4,487	62,493	684	356	1,040	527	107	634	17,968	2,315	20,283
80	55	45	53,640	4,978	58,618	632	395	1,027	488	119	606	16,616	2,568	19,184
90	50	50	49,198	5,477	54,675	580	435	1,014	447	130	578	15,240	2,826	18,065
100	46	54	44,751	5,977	50,728	527	474	1,002	407	142	549	13,862	3,084	16,946
110	41	59	40,373	6,470	46,842	476	513	989	367	154	521	12,506	3,338	15,844
120	37	63	36,132	6,947	43,078	426	551	977	328	165	494	11,192	3,584	14,776
130	33	67	32,088	7,401	39,489	378	587	966	292	176	468	9,940	3,818	13,758
140	29	71	28,289	7,828	36,118	333	621	955	257	186	444	8,763	4,039	12,802
150	25	75	24,771	8,224	32,995	292	653	945	225	196	421	7,673	4,243	11,916
160	22	78	21,555	8,586	30,141	254	681	935	196	204	400	6,677	4,429	11,106
170	19	81	18,650	8,912	27,563	220	707	927	170	212	382	5,777	4,598	10,375
180	16	84	16,054	9,204	25,259	189	731	920	146	219	365	4,973	4,748	9,721
190	14	86	13,757	9,463	23,220	162	751	913	125	225	350	4,261	4,882	9,143
200	12	88	11,741	9,689	21,431	138	769	907	107	231	337	3,637	4,999	8,636