Introduction
Literature review
Problem description
Modeling pickup and delivery service levels
Modeling transportation system
Modeling transportation network structure
Modeling transportation services
Modeling transportation process
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Step 1.1 A pickup start time is planned for the containers of a transportation order by considering: (1) satisfying pickup service level; and (2) balancing the carbon dioxide emissions and the in-transit inventory period at the rail terminal. And the containers start to be loaded on the trucks at the pickup start time.
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Step 1.2 After being loaded on the trucks, the containers depart from the origin immediately, and then arrive at the rail terminal by road service. After arriving at the rail terminal, the containers start to be unloaded from trucks immediately.
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Step 2.1 A rail service (i.e., a container block train) is selected based on a hard constraint that the time when the containers get loaded on it should not be later than its scheduled loading operation cutoff time. Containers should wait if the time when they get unloaded from trucks is earlier than the train’s scheduled loading operation start time, which leads to the in-transit inventory period.
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Step 2.2 After the loading is accomplished, containers should wait until the scheduled departure time of the train. The containers depart from the rail terminal along with the train and arrive at the successive terminal at the train’s scheduled arrival time.
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Step 2.3 After arrival at the rail terminal, the containers should wait until the scheduled unloading operation start time and then start to be unloaded from the train.
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Step 3.1 After the unloading is accomplished, the truck departure time is planned for the selected road service by considering: (1) satisfying delivery service level; and (2) balancing the carbon dioxide emissions and the in-transit inventory period at the rail terminal.
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Step 3.2 The containers depart from the rail terminal and arrive at the destination by road service. After arriving at the destination, the containers immediately start to be unloaded from the trucks. The transportation order when the unloading is accomplished.
Modeling uncertainty
Model formulation
Sets, indices, and parameters | Definitions |
---|---|
Symbols representing transportation orders | |
\(K\) | Set of transportation orders |
\(k\) | Index of a transportation order, and \(k\in K\) |
\( {\tau }_{k}\) | Index of the origin of transportation order \(k\) |
\({\epsilon }_{k}\) | Index of the destination of transportation order \(k\) |
\({q}_{k}\) | Volume in twenty feet equivalent unit (TEU) of the containers of transportation order \(k\) |
\(\left[{\pi }_{k}^{1},{\pi }_{k}^{2}, {\pi }_{k}^{3}, {\pi }_{k}^{4}\right]\) | Time window of picking up the containers of transportation order \(k\) at the origin |
\( {\xi }_{k}\) | Minimum pickup service level accepted by the shipper of transportation order \(k\), and \({\xi }_{k}\in \left[0, 1\right]\) |
\(\left[{\eta }_{k}^{1},{\eta }_{k}^{2}, {\eta }_{k}^{3}, {\eta }_{k}^{4}\right]\) | Time window of delivering the containers of transportation order \(k\) at the destination |
\({\varpi }_{k}\) | Minimum delivery service level accepted by the receiver of transportation order \(k\), and \({\varpi }_{k}\in \left[0, 1\right]\) |
Symbols representing road-rail intermodal transportation network | |
\(N\) | Set of the nodes in the network |
\(h, i, j\) | Indices of nodes in the network, and \(h, i, j\in N\) |
\({\Gamma }_{i}^{-}\) | Set of the predecessor nodes to node \(i\), and \({\Gamma }_{i}^{-}\subseteq N\) |
\({\Gamma }_{i}^{+}\) | Set of the successor nodes to node \(i\), and \({\Gamma }_{i}^{+}\subseteq N\) |
\(A\) | Set of directed arcs in the network |
\(\left(i, j\right)\) | Directed arc from node \(i\) to node \(j\) |
\(S\) | Set of transportation services in the network |
\(r, s\) | Indices of transportation services, and \(r, s\in S\) |
\({S}_{ij}\) | Set of transportation services on arc \(\left(i, j\right)\), and \({S}_{ij}={\Psi }_{ij}\bigcup {\Omega }_{\mathrm{ij}}\) |
\({\Psi }_{ij}\) | Set of rail services on directed arc \(\left(i, j\right)\) |
\({\Omega }_{ij}\) | Set of road services on directed arc \(\left(i, j\right).\) |
Symbols representing transportation services | |
\({d}_{ij}^{s}\) | Travel distance in km of transportation service \(s\) on directed arc \(\left(i, j\right).\) |
\({t}_{i}^{s}\) | Separate loading and unloading operation time in hour per TEU of transportation service \(s\) at node \(i\) |
\(\left[{l}_{i}^{s},{o}_{i}^{s}\right]\) | Scheduled loading and unloading operation time window of rail service \(s\) at node \(i\), where \({l}_{i}^{s}\) is the operation start time and \({o}_{i}^{s}\) is the operation cutoff time |
\({\tilde{g }}_{ijs}\) | Fuzzy capacity in TEU of rail service \(s\) on directed arc \(\left(i, j\right)\), and \({\tilde{g }}_{ijs}=\left({g}_{ijs}^{1},{g}_{ijs}^{2},{g}_{ijs}^{3},{g}_{ijs}^{4}\right).\) |
\(\theta \) | Free-of-charge inventory period in hour provided by rail services |
\({P}_{ij}^{s}\) | Set of the periods for road service \(s\) on directed arc \(\left(i, j\right)\) in the planning horizon |
\(p\) | Index of a period |
\(\left[{a}_{ijs}^{p}, {b}_{ijs}^{p}\right]\) | Interval of period \(p\) of road service \(s\) on directed arc \(\left(i, j\right)\), and \(p\in {P}_{ij}^{s}\) |
\({\tilde{t }}_{ijsp}\) | Fuzzy travel time in hour of road service \(s\) on directed arc \(\left(i, j\right)\) in period \(p\), and \({\tilde{t }}_{ijsp}=\left({t}_{ijsp}^{1},{t}_{ijsp}^{2},{t}_{ijsp}^{3},{t}_{ijsp}^{4}\right)\) |
Symbols representing carbon dioxide emissions | |
\({\tilde{e }}_{ijsp}\) | Fuzzy emission factor in kg per km per TEU of road service \(s\) on directed arc \(\left(i, j\right)\) in period \(p\), and \({\tilde{e }}_{ijsp}=\left({e}_{ijsp}^{1},{e}_{ijsp}^{2},{e}_{ijsp}^{3},{e}_{ijsp}^{4}\right)\) |
\({e}_{ij}^{s}\) | Emission factor in kg per km per TEU of rail service \(s\) on directed arc \(\left(i, j\right)\) |
Symbols representing costs | |
\({c}_{1}^{\mathrm{rail}}\) | Travel cost rate in Chinese Yuan (CNY) per TEU of rail services |
\({c}_{2}^{\mathrm{rail}}\) | Travel cost rate in CNY per TEU per km of rail services |
\({c}_{3}^{\mathrm{rail}}\) | Inventory cost rate in CNY per TEU per hour at rail terminals |
\({c}^{\mathrm{road}}\) | Travel cost rate in CNY per TEU per km of road services |
\({c}^{s}\) | Separate loading and unloading cost rate in CNY per TEU of transportation service \(s\) |
Symbols representing auxiliary parameters | |
\(L\) | A large enough positive number |
\(m\) | Index of a prominent point of a trapezoidal fuzzy number, and \(m\in \left\{1, 2, 3, 4\right\}\) |
Variables | |
\({x}_{ijs}^{k}\) | 0–1 binary decision variable: if the containers of transportation order \(k\) are moved from node \(i\) to node \(j\) by transportation service \(s\), \({x}_{ijs}^{k}=1\); otherwise \({x}_{ijs}^{k}=0\) |
\({w}_{ijsk}^{p}\) | 0–1 binary decision variable: if the containers of transportation order \(k\) are moved from node \(i\) to node \(j\) by road service \(s\) in period \(p\), \({w}_{ijsk}^{p}=1\); otherwise \({w}_{ijsk}^{p}=0\) |
\({u}_{i}^{k}\) | Non-negative deterministic decision variable representing the time when the containers of transportation order \(k\) start to be loaded on road service at node \(i\) before departure |
\({v}_{k}\) | Non-negative deterministic decision variable representing the pickup start time of the containers of transportation order \(k\) at the origin |
\({\tilde{y }}_{ik}\) | Non-negative trapezoidal fuzzy variable representing the time when the containers of transportation order \(k\) arrive at node \(i\) by road service and get unloaded, and \({\tilde{y }}_{ik}=\left({y}_{ik}^{1},{y}_{ik}^{2},{y}_{ik}^{3},{y}_{ik}^{4}\right)\) |
\({\tilde{z }}_{ijsk}\) | Non-negative trapezoidal fuzzy variable representing the waiting period in hour of the containers of transportation order \(k\) at node \(i\) before being loaded on rail service \(s\) on directed arc \(\left(i, j\right)\), and \({\tilde{z }}_{ijsk}=\left({z}_{ijsk}^{1},{z}_{ijsk}^{2},{z}_{ijsk}^{3},{z}_{ijsk}^{4}\right)\) |
\({\stackrel{\sim }{\delta }}_{ijsk}\) | Non-negative trapezoidal fuzzy variable representing the charged in-transit inventory period in hour of the containers of transportation order \(k\) at node \(i\) before being loaded on rail service \(s\) on directed arc \(\left(i, j\right)\), and \({\stackrel{\sim }{\delta }}_{ijsk}=\left({\delta }_{ijsk}^{1},{\delta }_{ijsk}^{2},{\delta }_{ijsk}^{3},{\delta }_{ijsk}^{4}\right)\) |
\({\varphi }_{ijs}^{k}\) | Non-negative deterministic representing the charged in-transit inventory period in hour of the containers of transportation order \(k\) at node \(i\) before being loaded on road service \(s\) on directed arc \(\left(i, j\right)\) |
Optimization objectives
Economic objective
Environmental objective
Constraints
Processing of the proposed FMOMINLP model
Model defuzzification to obtain a MOMINLP model
Defuzzification of the fuzzy objective functions
Defuzzification of the fuzzy constraints
Model linearization to obtain a MOMILP model
Interactive fuzzy programming approach
Objectives of MILP model | \({F}_{1}\) values | \({F}_{2}\) values |
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Minimize \({F}_{1}\) | \({F}_{1}\left({\Gamma }_{1}^{\mathrm{PIS}}\right)={F}_{1}^{\mathrm{PIS}}\) | \({F}_{2}\left({\Gamma }_{1}^{\mathrm{PIS}}\right)={F}_{2}^{\mathrm{NIS}}\) |
Minimize \({F}_{2}\) | \({F}_{1}\left({\Gamma }_{2}^{\mathrm{PIS}}\right)={F}_{1}^{\mathrm{NIS}}\) | \({F}_{2}\left({\Gamma }_{2}^{\mathrm{PIS}}\right)={F}_{2}^{\mathrm{PIS}}\) |
Empirical case study
Case design
Case description
Abbreviations | Rail terminals | Locations |
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BT | Baotou Railway Station | Baotou City, Inner Mongolia |
HHT | Hohhot Railway Station | Hohhot City, Inner Mongolia |
HN | Huinong Railway Station | Shizuishan City, Ningxia |
YCS | Yinchuan South Railway Station | Yinchuan City, Ningxia |
QTX | Qingtongxia Railway Station | Wuzhong City, Ningxia |
XZ | Xinzhu Railway Station | Xi’an City, Shaanxi |
CX | Chengxiang Railway Station | Chengdu City, Sichuan |
PT | Putian Railway Station | Zhengzhou City, Henan |
XG | Xingang Railway Station | Tianjin City |
JZ | Jiaozhou Railway Station | Qingdao City, Shandong |
HD | Huangdao Railway Station | Qingdao City, Shandong |
YP | Yangpu Railway Station | Shanghai City |
Parameters | Values | Units | Sources |
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\({c}_{1}^{\mathrm{rail}}\) | 440 | CNY per TEU | [69] |
\({c}_{2}^{\mathrm{rail}}\) | 3.185 | CNY per TEU per km | [69] |
\({c}_{3}^{\mathrm{rail}}\) | 3.125 | CNY per TEU per hour | [69] |
\({c}^{\mathrm{road}}\) | 6.0 | CNY per TEU per km | [70] |
\({c}^{s}\) | 195 (\(s\) = rail); 25 (\(s\) = road) | CNY per TEU | |
\({t}_{i}^{s}\) | 0.2 (\(s\) = rail); 0.05 (\(s\) = road) | h per TEU | [71] |
\(\theta \) | 6.0 | h | Set by this study |
No. | Origins | Destinations | Volumes in TEU | Pickup time windows | Delivery time windows |
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1 | LZ | LYGP | 21 | [5, 9, 12, 14] | [90, 95, 103, 111] |
2 | LZ | LYGP | 19 | [20, 24, 28, 33] | [135, 142, 152, 161] |
3 | LZ | LYGP | 14 | [10, 14, 18, 24] | [126, 133, 142, 149] |
4 | LZ | LYGP | 16 | [16, 20, 25, 29] | [80, 88, 98, 106] |
5 | LZ | LYGP | 32 | [22, 28, 34, 38] | [134, 140, 148, 154] |
6 | LZ | LYGP | 16 | [7, 13, 18, 22] | [102, 110, 119, 125] |
7 | LZ | LYGP | 22 | [26, 30, 36, 42] | [125, 133, 142, 148] |
8 | LZ | LYGP | 32 | [30, 37, 42, 46] | [140, 145, 155, 163] |
9 | LZ | LYGP | 30 | [12, 15, 19, 23] | [95, 102, 112, 119] |
10 | LZ | LYGP | 25 | [19, 23, 29, 35] | [126, 135, 144, 151] |
Computing environment
Number of variables | Number of integer variables | Number of constraints |
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3559 | 1120 | 7672 |
Optimization results and analysis
Pareto solutions to the empirical case
Economic objective values in CNY | Environmental objective values in kg | |
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Minimize of the total costs | 2,511,642 | 388,544.3 |
Minimize of the emissions | 2,527,123 | 383,117.9 |
\(\mathrm{LB}\) | Satisfaction degrees | Objective values | CPU time (s) | ||
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\(\mu \left({F}_{1}\right)\) | \(\mu \left({F}_{2}\right)\) | \({F}_{1}\) (Total costs in CNY) | \({F}_{2}\) (Total emissions in kg) | ||
0 | 1.0 | 0 | 2,511,642 | 388,544.3 | 40 |
0.1 | 0.978 | 0.111 | 2,511,982 | 387,939.5 | 38 |
0.2 | 0.968 | 0.231 | 2,512,137 | 387,293.4 | 26 |
0.3 | 0.966 | 0.305 | 2,512,162 | 386,889.2 | 34 |
0.4 | 0.913 | 0.406 | 2,512,982 | 386,342.6 | 40 |
0.5 | 0.839 | 0.587 | 2,514,130 | 385,358.0 | 38 |
0.6 | 0.818 | 0.645 | 2,514,447 | 385,044.6 | 42 |
0.7 | 0.807 | 0.818 | 2,514,625 | 384,107.1 | 32 |
0.8 | 0.807 | 0.818 | 2,514,625 | 384,107.1 | 31 |
0.9 | 0.766 | 0.909 | 2,515,262 | 383,613.8 | 29 |
1.0 | 0 | 1.0 | 2,527,123 | 383,117.9 | 32 |