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Vehicle routing using remote asset monitoring: a case
study with Oxfam
Fraser McLeod, Tom Cherrett (Transport)
Güneş Erdoğan, Tolga Bektas (Management)
OR54, Edinburgh, 4-6 Sept 2012
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Problem summary (requirements)
• Visit shops on fixed days• Visit banks before they become full• Routes required Monday to Friday each
week• Start/end vehicle depot• Single trips each day (i.e. no drop-offs)
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Problem summary (constraints)
• Heterogeneous vehicle fleet– 1 x 1400kg (transit van)– 3 x 2500kg (7.5T lorry)
• Driving/working time constraints• Time windows for shops
Objectives• Maximise profit (£X per kg – £1.50 per
mile)– where X = f(site) (e.g. 80p/kg from banks; 50p/kg from shops)
• Avoid banks overfilling– prevents further donations (= lost profit)– upsets site owners– health and safety
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Data (locations, time, distance)
• Postcodes for 88 sites:– 1 depot– 37 bank sites– 50 shops
• Driving distances/times between 3828 (= 88x87/2) pairs of postcodes– Commercial software– Times calibrated using recorded driving
times
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Data (demand)
• Weights collected from shops and banks (April 2011 to May 2012)
• Remote monitoring data (from July 2012)
• Shop demand = average accumulation rate x no. of days since last collection
• Bank demand – randomly generated
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Assumptions (bank demand)
• Demand at bank i, day j = Xi,j
= max(Xi,j-1 + di,j-1, bank capacity)
where d = donations = Yi,j.Zi,j
Y = Bernoulli (P = probability of donation)Z = N( , m s) = amount donated
• m = mean daily donation amount, excluding days where no donations are made
• s estimated from collection data• bounded by [0, bank capacity]
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Solution approach
• Look ahead period = 1 day (tomorrow)• Minimum percentage level to be
collected– (50% and 70% considered)
• Overfilling penalty (applied to banks not collected from)– fill limit (%) (75% and 95% considered)– financial penalty (£/kg) (£10/kg considered)
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Solution approach
• Tabu search – Step 1 (Initialization) – Step 2 (Stopping condition): iteration
limit– Step 3 (Local search): addition, removal
and swap – Step 4 (Best solution update)– Step 5 (Tabu list update)– Go to Step 2
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Results / KPIs
• 20 consecutive working days • 3 random starting seeds• Performance indicators
– # bank visits– profit– distance– time– weight collected and lost donations
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Results (# bank visits)Probability of donation
Penalty fill level
Exist-ing
50% 70% Exist-ing
50% 70% Exist-ing
50% 70%0
50
100
150
200
250 240
8165
240
125
96
240
135
102
Minimum collection
bank
vis
its in
20
days
p = 0.8p = 0.5p = 0.2
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Profit
Exist-ing
50% 70% Exist-ing
50% 70% Exist-ing
50% 70%0
10
20
30
40
50
60
70
80
90
100
57.608 59.659 57.99664.049 65.036 64.535 65.754 65.727 64.804
Minimum collection
proft
(£/1
000)
p = 0.8p = 0.5p = 0.2
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Distance
Exist-ing
50% 70% Exist-ing
50% 70% Exist-ing
50% 70%0
4000
8000
12000
16000
20000
13714 13331 1309313819 14270
13544 14036 1450013938
Minimum collection
dist
ance
(km
)p = 0.8p = 0.5p = 0.2
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Time
Exist-ing
50% 70% Exist-ing
50% 70% Exist-ing
50% 70%0
100
200
300
400
500
600
700
800
900
1000
738684 671
737 725 700745 728 712
Minimum collection
time
(hou
rs)
p = 0.8p = 0.5p = 0.2
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Weight
Existing 50% 70% Existing 50% 70% Existing 50% 70%0
4
8
12
16
20
0.3652 0.2138 0.35650.2975 0.0773 0.1903 0.1762 0.0581 0.1329
Minimum collection
wei
ght c
olle
cted
& lo
st d
onati
ons
(kg/
1000
)p = 0.8p = 0.5p = 0.2