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Two-Tiered City Logistics Modelling Demand Uncertainty in Tactical Planning
Teodor Gabriel [email protected]
Colloque Logistique Urbaine et Interdisciplinarité, ParisLe 27 novembre 2014
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© Teodor Gabriel Crainic 20142
City Logistics Ideas
“New” organizational strategies/models Reduce & control freight vehicle flows & types Improve efficiency of freight transportation
Higher loads, less empty vehicle-km Reduce environmental footprint & congestion &
interference with people impact Without penalizing its economic activities To foster an efficient transportation system To make the city a better place to experience: live, work,
visit, move within and through … Work on demand & supply sides + behaviour, policy,
regulation, law, …
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© Teodor Gabriel Crainic 20143
Move Freight Differently, “Out of the Way”
Underground automated systems: new supply systems Conveyor belts or adapted vehicles on particular
infrastructure Particular packing Loading/unloading stations Huge investments required
Night deliveries: Move the demand out in time Successful pilot in New York city – much interest
elsewhere Requires particular city regulations Does not necessarily decrease number of vehicles
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© Teodor Gabriel Crainic 20144
Move Freight Differently (2)
Most actual systems, past projects and proposals are based somehow on the principle of
Consolidation and coordination Coordination of shippers and carriers (& consignees) Consolidation of several shipments of different
shippers & carriers into, and delivery by the same (improved, more energy efficient, “green”) vehicle
Makes use of one or a series of terminals Consolidation facilities, Urban / city distribution /
logistics centers, of various sizes and roles
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© Teodor Gabriel Crainic 20145
The City Logistics (Supply) Fundamental Idea
An integrated logistics system = Shippers, shipments Carriers (all modes including passenger and
interurban, e.g., rail, navigation), vehicles Service providers, consignees/customers, …
Optimize this logistics system “Public system” view (not ownership!) operated as best
fits the local culture, laws and regulations
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© Teodor Gabriel Crainic 20146
Single-Tier Single-CDC City Logistics
Customerzone
Urban vehicle
CityDistributionCenter
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© Teodor Gabriel Crainic 20147
City Logistics for Large or Sensitive Urban Areas
Most display a two-tier structure Loads consolidated at CDC into “large” vehicles Moved to CDC-like facilities – satellites – “close” to
customers Transferred to “small” vehicles appropriate for city
center Delivered to final destinations
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© Teodor Gabriel Crainic 2014
SS S
SS
SP
P
P
Center 1Center 2
Origin-node
AirportRailway station
Navigation Terminals
Platforms
Depots
Satellites
Multi-Tiered City Logistics
SRailway station
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© Teodor Gabriel Crainic 201410
City freighter - route
Urban vehicle - route
Empty vehicle
Two-Tier City Logistics
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© Teodor Gabriel Crainic 201411
2T-CL with Rail & Transit (Public Transport)
Navigation
Long-Haul Trucks
Rail
City Freighter
Urban Vehicle
Satellite Crossdock
Customer
Distribution center
City route
City Distribution Center
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© Teodor Gabriel Crainic 201412
City Logistics for Large Cities
Several not necessarily integrated sub-systems Many have access to some public infrastructure (light rail
lines, parking lots, …) even for private initiatives A few initiatives to use dynamically available
transportation & storage capacity An implicit idea: Disconnect the actual mean of
transportation / delivery from the carrier/shipper/3PL originally contracted
Private inititive implementing CL operating principles Multimodal systems that aim for intermodality
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© Teodor Gabriel Crainic 201413
Modular & Standard Physical Internet -Containers
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© Teodor Gabriel Crainic 2014
Ship
Long-distancevehicle
Train
City freighter
Plane
Bicycle
Urban vehicle
Urban hub
Interconnected, Multi-tiered City Logistics
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© Teodor Gabriel Crainic 201415
Challenges & Opportunities
CL = complex consolidation-based transport system Multiple “layers”, facilities, fleets, modes Time restrictions, dependencies, synchronization
Goal of sustainable efficiency for stakeholders & city Operations Research & Transportation Science
“New” problems New models, algorithms, instruments
Methods for the system and its components Appropriate for the decision-level concerned
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© Teodor Gabriel Crainic 201416
Challenges & Opportunities (2)
Culturally and socially-aware organization and business models, e.g.,
Cultural (government ↔ people & business, business models, taxation, etc.) impact and need for somewhat tailored solutions
Stakeholder behaviour modelling Demand identification and modelling Partnerships & collaborations → Supply modelling Public policy Materials (“boxes”), law, regulation, land use, …
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© Teodor Gabriel Crainic 201417
An illustration of O.R. development:Uncertainty and tactical planning
Nicoletta Ricciardi (Sapienza U. di Roma)Walter Rei (UQAM)
Fausto Errico (CIRRELT)
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© Teodor Gabriel Crainic 201418
Tactical (Medium-term) Planning
season
day
• Tactical planning = Plan regular operations, based on a (point) forecast, for efficient resource allocation & utilization, customer satisfaction, profitable operations
• Day-to-day situation generally different from forecast
XBuild
the plan
Adjust the plan
X
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© Teodor Gabriel Crainic 201419
Accounting for Uncertainty
season
day
Tactical medium-term planning accounting for uncertainty = Integrate into the tactical planning model/method the possible “adjustments” and their costs
XBuild a more flexible and robust plan
Adjust the plan “less”
X
System dataForecast demand
Observed demand
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© Teodor Gabriel Crainic 201420
Sources of Uncertainty in City Logistics
Time Work at facilities & service at customers Travel through the city
Demand (regularity of activities within customer zones) Volume (including no show; volume = 0) Unexpected
Rare but predictable events (e.g., vehicle or infrastructure incidents)
Rare, “catastrophic” events
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© Teodor Gabriel Crainic 201421
Demand Uncertainty & Planning
Robust plans (flexible operations) versus managerial concerns
Build a season plan based on available/forecast data Each “day”, once the uncertain demand data is resolved
Keep part/most of the plan External and satellite facility utilization Urban-vehicle service network
Adjust using a recourse policy Routing city freighters and extra vehicles
Two-stage modelling
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© Teodor Gabriel Crainic 201422
Two-Stage Modelling Framework
Two-stage recourse formulation First stage
Selection of first-tier services (& departure times) Allocation of customers to services & satellites
Second stage Routing of second-tier city freighters Service adjustment (eventually) Customer-to-satellite allocation (eventually) Calling on extra vehicles (when required)
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© Teodor Gabriel Crainic 201423
Two-Stage Stochastic Programming
A priori optimization
First-stage decisions: the a priori plan x : Realization of demand for : Cost of “optimal” operation plan using
the a priori plan for demand given a recourse policy RP
DMinimize ( ) E ( ( , ( ))
Subject to ,
RPDf x Q x D
x X
( )D ( , ( ))RPQ x D
( )D
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© Teodor Gabriel Crainic 201424
Problem Elements: Facilities & Customers
d
External zone
, , ,z zz
: , , , ,[ , ], ( )d p vol e c a b d
e
Satellite
Customer demand
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© Teodor Gabriel Crainic 201425
Scheduled Urban-Vehicle Services
r’: t(r’)=t
r: t(r)=t+1
Decision: Whichservice to run?(When?)
e
s
(r) {1,0}
r’: t(r’)=t; (r)={z}
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© Teodor Gabriel Crainic 2014
st
s’t+
c4
gt- g’t++
e’t’
e’’’t’’’e’’t’’
c2
c3
c4
c1c5
c6
c7
c8
c8
c3
c2
c1
c5
c7
c6
City-Freighter Work Segment & Assignment
(h) {1,0}
Decision: Whichc-f work assignment to operate?
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© Teodor Gabriel Crainic 201427
Demand Itineraries
m:{e,r(m),t(m) < t(r),z(m)=z(m) (r(m)),(p(d)), l(h(m)), c(d)}
d
z’
z
Select itinerary to deliver cargo on time:(m) {1,0}
ed: e,c,p,t,[a,b],vol
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© Teodor Gabriel Crainic 201428
First Stage
Information considered System data Estimation of future demand
Defining an a priori plan Aggregated service network design model with
approximate routing costs (Tr. Sc. 2009) Decision variables
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© Teodor Gabriel Crainic 201429
First Stage FormulationGeneralized costfirst-tier services
Generalized cost second-tier work assignments – forecast demand Recourse cost
U. Vehicle capacityLinking
Single itinerary
Satellite capacityU. Vehicles
C. Freighters
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© Teodor Gabriel Crainic 201431
Second Stage – Observing the Demand
All demands Forecasts Determine routing =
Synchronized, scheduled, multi-depot, multiple-tour, heterogeneous VRPTW
Attempt to improve system response =Apply a recourse policy + routing
Adjust plan + routing, otherwise Straightforward to determine which customers need
extra capacity to be serviced
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© Teodor Gabriel Crainic 201432
2nd Stage Recourse Policies
Routing (R) Routing & possible customer re-assignment (RA) Service Dispatch and Routing (SR) Service Dispatch, Routing & possible customer re-
assignment (SRA) Increased latitude in the recourse actions Extra city freighters with high cost for the demand that
cannot be moved by regular vehicles A single city-freighter fleet to service the “regular”
and the “extra” demand Direct-shipment policy
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© Teodor Gabriel Crainic 201433
3-Leg City Freighter Work Segment
zt
z’t++
i ’’
k’’
j ’’
h’’
i
k
j
h
gt-
g’t+++
et+
i ’
k’
j’
h’
Direct shipment
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© Teodor Gabriel Crainic 201434
2nd Stage Routing Recourse
Keep Selected first-tier services (routes and schedules) Customer-to-satellite assignments Bounds on
second-tier vehicle departures at each rendez-vous point (satellite, period)
Optimize the routing & demand itineraries
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© Teodor Gabriel Crainic 201437
2nd Stage Route & Reassign Recourse
Keep Selected first-tier services (routes and schedules)
Relax the customer-to-satellite rendez-vous assignments Optimize the routing & demand itineraries without pre-
assignment of customers to satellites Same formulation, larger set of itineraries, simpler
stochastic formulation
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© Teodor Gabriel Crainic 201438
2nd Stage Service Dispatch and Routing Recourse
Keep Selected first-tier services (routes and schedules) Customer demands to be served from each (satellite,
period) point Identify satellite opportunity windows and urban-vehicle
compatible services
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© Teodor Gabriel Crainic 2014
Output of Service Network Design
zt
i
j
k
et’
or
ztC
[ ( ), ( )]a k b k[ ( ), ( )]a j b j
[ ( ), ( )]a i b i( )id
( )jd ( )kd
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© Teodor Gabriel Crainic 2014
Opportunity Windows and Compatible Services
zt
i
j
k
et’
ztC
or
[ ( ), ( )]o oa r b r
[ ( ), ( )]a k b k
[ ( ), ( )]a i b i
[ ( ), ( )]a j b j
[ ( ), ( )]a zt b zt
( )jd
( )id
( )kd
( )oR r
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© Teodor Gabriel Crainic 201441
2nd Stage Service Dispatch and Routing Recourse
Optimize the restricted selection of services, the routing of regular and extra city freighters & demand itineraries: restricted tactical model With and without fixed customer-to-rendez-point
assignment
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© Teodor Gabriel Crainic 201444
Experimental Study of Recourse Alternatives
System performance & management issues Monte Carlo-like simulation
Not an evaluation of the value of stochastic model
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© Teodor Gabriel Crainic 201445
Experimental Setup
The four recourse strategies No tactical plan but daily plan = “the day before” A simplified setting: single product & vehicle type, fixed
travel times, no split Data sets randomly generated – “small” dimensions
(including with realistic geographical settings) 1-2 external zones, 2-3 satellites, 15 & 25 customer
zones, 6 periods of 25 minutes (2.5 hours) 2 demand-size distributions, 2 prediction values
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© Teodor Gabriel Crainic 201448
Experimental Setup (2)
Analyses based on Traffic intensity: numbers of vehicles, vehicle-km Vehicle (capacity) utilization System cost Impact & social cost Managerial concerns
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© Teodor Gabriel Crainic 201449
Cost Analysis
No-planning = Lower bound on costs & no direct deliveries (extra vehicles); Management (e.g., labor)?
Cost of planning ≈15% and but extra vehicles More flexibility = less direct services (60%, lower
variance) & costs (2% - 3.5%) Direct services: ↑nb. Customers, ↓nb. of CDC Do not use the “average” forecast
Recourse 1s2l 2s2l 2s2l_std DirectDel avg#DD R 20941 22900,4 10% 7878,2 2,8RA 20938,9 22087,1 11% 366,9 1,3NO 18311,7 18506,2 13% -3265,8 0 SR 20947,5 23041,5 10% 7871,7 2,8
SRA 20899,9 22538,8 11% 91,3 1,2
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© Teodor Gabriel Crainic 201450
Route Length Analysis
More flexibility = shorter city-freighter routes (4,8%) and less empty travel (6%)
Higher empty travel with # of customers Lower empty travel with # of external zones / satellites Modifying – sliding – the urban-vehicle departures
appears beneficial
Recourse 2s1l 2s2l 2s2l_std Empty c-f R 64.8 318.6 37.6 156.4RA 64.8 298.4 36.2 147.0NO 80.4 233.4 29.3 118.6 SR 64.8 321.8 38.8 157.2
SRA 65.2 303.3 36.7 149.6
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© Teodor Gabriel Crainic 201451
Vehicle Capacity Utilization
No planning = few more vehicles 1st level, less on 2nd
Planning yields very good loading factors More flexibility yields better vehicle loadings (≈ 15%) Most city freighters operate a single leg, a few two
Need to investigate “waiting” strategies (synchronization is hard)
Recourse Urban vehs. City freighters avg#DD C-f WSeg U-v load C-f load R 4,5 10,2 2,8 11,4 77% 79,30%RA 4,5 10,2 1,3 11,1 88,40% 81,10%NO 4,6 9,2 0 9,5 85,60% 82,60% SR 4,5 10,2 2,8 11,5 77% 78,80%
SRA 4,5 10,4 1,2 11,3 88,40% 79,40%
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Satellite Utilization
System appears stable Increasing flexibility, increases the “volatility” of using
the satellites Trade off to find between operation flexibility and
management concerns Need of ITS
Recourse veh1l veh2l custAssR 0 0,1 0,1
RA 0 0,1 0,2NO 0,3 0,7 1,1SR 0,2 0,4 0,8
SRA 0,3 0,6 1,1
Standard deviations
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© Teodor Gabriel Crainic 201453
Conclusions and Perspectives
Flexibility in adjusting the plan is beneficial on all counts: costs, km performed, capacity utilization …
It might come with higher requirements for management (& labor relations and work rules) flexibility
Needs advanced IT and decision-support systems NOW: Address the stochastic models (and the deterministic ;-) Large dimensions City Logistics systems design, policies, financing, …