Clean and ze o-emission u ban buses: Compliance wi h EU egula ions and
lee ansi ion in Se ille
M.A. Tagua Na a e e
a,*
, J. Se ano Reyes
a
, J.A. V´
elez Godi˜
no
b
,
F.J. Jim´
enez-Espada o Aguila
a
a
Depa men o Ene gy Enginee ing, School o Enginee ing, Uni e si y o Se ille, Camino de los Descub imien os S/N, 41092, Se ille, Spain
b
Depa men o Cons uc ion Enginee ing and Enginee ing P ojec s, School o Enginee ing, Uni e si y o Se ille, Camino de los Descub imien os S/N, 41092, Se ille,
Spain
ARTICLE INFO
Handling edi o : X Ou
Keywo ds:
EU egula ions
CO
2
emissions
Ba e y elec ic buses
CNG buses
Ene gy consump ion o u ban buses
Flee ansi ion
ABSTRACT
The EU public anspo sec o is domina ed by diesel and na u al gas buses, bu lee s uc u es a e apidly
changing. EU clima e laws d i e wo s a egies: one o bus manu ac u e s and ano he o public anspo
ope a o s (PTO), wi h di e en imelines. PTOs mus p og essi ely eplace lee s wi h clean and ze o-emission
buses. This pape de elops bus eplacemen s a egies aligned wi h EU s anda ds, ocusing on cos minimiza-
ion and CO
2
emission educ ion. Th ee p opulsion echnologies (diesel, comp essed na u al gas, and elec ic)
and wo bus ypes ( egula and a icula ed) a e analyzed. The s a egies conside acquisi ion, ope a ional, and
se ice cos s, along wi h CO
2
emissions. The p oposed app oach, applied o e a 10-yea pe iod, uses eal-wo d
da a om Se ille (Spain) PTO o mee EU s anda ds o 2025–2035. Ope a ional da a allow p ecise ene gy
demand es ima ion, conside ing p opulsion, clima iza ion ai comp esso , and auxilia ies. CO
2
emissions cal-
cula ions show ha CNG buses emi 24 % mo e CO
2
pe km han diesel buses. Op imiza ion esul s indica e ha a
CO
2
minimiza ion s a egy educes emissions by 16.3 %, wi h only a 6.7 % cos inc ease compa ed o he
minimal-cos s a egy.
1. In oduc ion
The ansi ion owa d sus ainable u ban anspo is a global p io i y
d i en by en i onmen al conce ns, emissions egula ions, and clean
ene gy ad ances. In 2022, anspo accoun ed o 23 % o global CO
2
emissions [1], and in he EU, i con ibu ed 29,7 %, wi h oad anspo
esponsible o abou 60 % o ha –o e 25 % om hea y-du y ehicles
and buses [2]. Wi h 70 % o i s popula ion li ing in u ban a eas [3], he
EU p omo es sus ainable, low-emission u ban mobili y h ough policies
like he U ban Mobili y F amewo k [4], emphasizing public anspo ,
clean, sa e and connec ed al e na i es. Simila ly, sec o s such as In o -
ma ion and Communica ion (ICT) a e inc easingly engaging in e o s o
educe CO
2
emissions, in alignmen wi h policy a ge s es ablished in EU
[5] and echoed in o he egions, including A ab coun ies, whe e s udies
ha e highligh ed he need o s a egic ac ion [6,7].
F om egula o y s andpoin , he EU p omo es sus ainable anspo
h ough he Eu opean G een Deal, a s a egic plan o achie e clima e
neu ali y by 2050. This ini ia i e was o malized in Communica ion
COM (2019) 640 [8], which ou lines key policies o educe emissions,
os e clean ene gy adop ion, and suppo sus ainable economic g ow h.
EU is p omo ing he use o al e na i e uels wi h he Regula ion EU
2023/1804 [9] was app o ed in Sep embe 2023, in line wi h he ob-
jec i es o he Eu opean G een Deal. Toge he wi h his Regula ion, he
Di ec i e 2019/1161 [10] da e om June 20, 2019, which p omo es
clean and ene gy-e icien oad anspo ehicles, includes an upda e o
he de ini ion o al e na i e uels. This Di ec i e a e ansposed in o
Spanish Law. The Di ec i e is mo i a ed by he EU commi men s o
educe g eenhouse gas emissions by a leas 40 % by 2030 compa ed o
1990 le els, o inc ease he consump ion o enewable ene gy by a leas
27 %, and o achie e ene gy sa ings o no less han 27 %. Wi hin his
Di ec i e, se e al ehicle ca ego ies a e de ined in acco dance wi h
Regula ion (EU) 2018/858 [11]. Among hem, ca ego y M
3
co esponds
o u ban buses. This classi ica ion speci ies ehicle ypes based on hei
uel o ene gy sou ce, including.
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (M.A. Tagua Na a e e).
Con en s lis s a ailable a ScienceDi ec
Ene gy
jou nal homepage: www.else ie .com/loca e/ene gy
h ps://doi.o g/10.1016/j.ene gy.2025.137025
Recei ed 19 Ma ch 2025; Recei ed in e ised o m 5 June 2025; Accep ed 6 June 2025
Ene gy 332 (2025) 137025
A ailable online 13 June 2025
0360-5442/© 2025 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY license (
h p://c ea i ecommons.o g/licenses/by/4.0/ ).
•Clean ehicles: Those ha use al e na i e uels o ene gy sou ces ha
eplace, a leas in pa , adi ional ossil uels and ha can
con ibu e o deca boniza ion, including: Elec ici y, hyd ogen,
ammonia, syn he ic pa a inic uels (HVO), bio uels, na u al gas in
gaseous o m (CNG) and lique ied o m (LNG), and lique ied pe o-
leum gas (LPG). In he case o liquid, syn he ic, o pa a inic bio uels,
mixing wi h con en ional ossil uels is no allowed. Excluded om
he abo e a e uels p oduced om aw ma e ials wi h a high isk o
indi ec land-use change, o which he e is a signi ican expansion o
he p oduc ion a ea on lands wi h high ca bon s ock.
•Ze o-emission ehicles: Clean ehicles wi hou an in e nal combus-
ion engine (ICE), o wi h an ICE ha emi s han 1 g o CO
2
/kWh
(measu ed in acco dance wi h Regula ion (EC) No 595/2009) o
emi s less han 1 g o CO
2
/km (measu ed in acco dance wi h Regu-
la ion (EC) No 715/2007).
Wi h cu en echnology, ze o-emission ehicles a e ypically
de ined as hose powe ed by ba e ies o hyd ogen uel cells (HFC).
Howe e , se e al manu ac u e s — including Vol o, Wes Po , MAN,
and IVECO — ha e al eady de eloped in e nal combus ion engines ha
ope a e exclusi ely on hyd ogen and a e expec ed o ecei e app o al by
2025 [12,13]. As a esul , he echnological landscape o ze o-emission
ehicles is poised signi ican ly in he nea u u e.
In addi ion o he p e iously men ioned de ini ion o al e na i e
uels used in ehicles wi hin he a ge ca ego y, Di ec i e (EU) 2019/
1161 se s minimum p ocu emen a ge s ha each EU Membe S a e
mus mee ega ding he public pu chase o M
3
ca ego y ehicles o
public anspo . Fo Spain, he a ge s es ablished by his Di ec i e a e
p esen ed in Table 1.
I is wo h highligh ing ha he p e ious s anda d applies exclusi ely
o he p ocu emen o new buses, no o he exis ing lee . Fu he mo e,
by Decembe 31, 2027, he Eu opean Commission (EC) is equi ed o
e iew he implemen a ion o Di ec i e 2009/33/EC and p opose new
legisla ion applicable beyond 2030, om which addi ional egula o y
cons ain s a e an icipa ed. Consequen ly, lee enewal s a egies
should be designed wi h su icien lexibili y o accommoda e hese
po en ial legal modi ica ions.
Regula ions a ge ing bus manu ac u e s mus also be aken in o
accoun . A key example is he Regula ion o he Eu opean Pa liamen
and o he Council o May 24, 2024, which ein o ces CO
2
emissions
s anda ds o new hea y-du y ehicles and es ablishes manda o y
epo ing obliga ions [14]. Acco ding o his egula ion, bus manu ac-
u e s a e equi ed o comply wi h he implemen a ion schedule p e-
sen ed in Table 2.
Regula o y amewo ks signi ican ly in luence u ban anspo op-
e a ions, pa icula ly h ough PTO which play a cen al ole in he EU
deca boniza ion e o s by aligning lee enewal wi h legal, echno-
logical, and en i onmen al a ge s. The ansi ion o clean o ze o-
emission ehicles manda ed by legisla ion poses in ica e economic
and ope a ional challenges. Cu en egula ions equi e PTOs o phase
ou non-complian ICE ehicles du ing new bus p ocu emen , d i en by
aging lee s and egula o y p essu e o educe g eenhouse gas emissions.
S a ing in 2035, EU-based manu ac u e s mus supply ze o-emission
buses o PTO, ma king a pi o al shi as ou lined in Table 2.
T adi ionally powe ed by diesel o comp essed na u al gas (CNG),
PTO lee s inc easingly conside elec i ica ion, ci ing ba e y elec ic
buses (BEB) as cleane and mo e ene gy-e icien al e na i es [2,15].
This e olu ion necessi a es s a egic amewo ks o decision-making
ha encompass economic iabili y, en i onmen al impac assess-
men s, and ope a ional con inui y. The shi om diesel and CNG o
elec ic and o he low-emission echnologies, including HFC, demands
ca e ul op imiza ion in iming, scale, and long- e m inancial planning.
Add essing hese complexi ies equi es holis ic app oaches ha balance
economic easibili y, en i onmen al sus ainabili y, and se ice
eliabili y.
This challenge is o mally e e ed o as he bus lee eplacemen
p oblem (BFRP), which in ol es he sys ema ic and cos -e ec i e sub-
s i u ion o con en ional buses wi h cleane al e na i es o e a de ined
planning ho izon. The BFRP is shaped by a ious in e dependen ac o s,
including high up on in es men cos s, ope a ional sa ings po en ial,
emissions educ ion goals, and he in as uc u e equi ed o suppo
new p opulsion echnologies —pa icula ly elec ic and hyd ogen-based
sys ems. Mo eo e , sol ing he BFRP equi es main aining a delica e
balance be ween se ice eliabili y and en i onmen al objec i es, all
while minimizing dis up ions o PTO.
Se e al s udies ha e in es iga ed he BFRP, signi ican ly b oadening
i s scope beyond adi ional cos minimiza ion o encompass he chal-
lenges o deca boniza ion and echnological ansi ion. Op imiza ion
models – equen ly employing Mixed-In ege P og amming – and he
ehicle cha ac e iza ion, lee capaci y and in o ma ion and pe iod o
analysis a e cen al o his esea ch. These models ypically aim o
minimize o al Li e Cycle Cos (LCC), as in he wo k o F ieβ & P e schy
[16], who analyzed a ze o-emission mixed lee and demons a ed he
ad an ages o a echnology-di e se composi ion. This wo k p esen s
simila i ies wi h [16] in he sense ha i includes he exploi a ion cos o
he ac ual bus lee , which also exhibi s echnological di e si y. How-
e e , i is o ien ed owa d he end use — he PTO—and in his ega d, i
add esses bo h cos issues and compliance wi h manda o y EU egula-
ions. To he au ho s’ knowledge, he e is cu en ly no esea ch wo k
ha add esses bo h aspec s simul aneously. Islam & Lownes [17], o
ins ance, de eloped a dual-objec i e app oach add essing bo h LCC and
GHG emissions, iden i ying op imal solu ions based on he in eg a ion o
BEB and Hyb id Elec ic Buses (HEB), ou wo k simila ly add esses dual
objec i es (cos and CO
2
minimiza ion) bu as sepa a e op imiza ion
goals, ocusing on a di e en echnological mix. Unde unce ain y,
A enali e al. [18] applied eal op ions o de e mine op imal eplace-
men iming and echnology adop ion, epo ing up o 10 % To al Cos o
Owne ship (TCO) sa ings when lee enewal is an icipa ed; in ou
cu en wo k, al hough employing a dis inc op imiza ion amewo k,
TCO conside a ions a e expanded o include a mo e g anula cos
b eakdown, such as speci ic ope a ional expenses (main enance,
pe sonnel) and he sal aged alues o ehicles and BEB ba e ies.
Fu he mo e, S asko & Gao [19] explo ed he in e play be ween
acquisi ion, e o i ing, and ask assignmen decisions, showing ha
CNG buses can be p o i able unde app op ia e CO
2
p icing schemes; ou
app oach di e s by di ec ly modelling EU egula o y a ge s o lee
composi ion o e a 10-yea ho izon, analysing he eplacemen o diesel,
CNG and BEB buses based on eal-wo ld ope a ional da a, a he han
ocusing on CO
2
p icing schemes, e o i ing, o ask assignmen . O he
s udies – such as Ribei o & Mendes [20] – ocused on policy-d i en lee
enewal c i e ia, including ehicle age h esholds; while ou s udy is also
policy-d i en, i applies speci ic EU p ocu emen a ge s (pe cen ages o
Table 1
Pe cen ages equi ed o public companies o he pu chase o hea y ehicles o
public anspo .
Bus (Ca ego y
M3)
F om Augus 2, 2021, o
Decembe 31, 2025
F om Janua y 1, 2026, o
Decembe 31, 2030
Clean ehicles 45 % 65 %
Ze o-emission
ehicles
A leas 50 % o he clean ehicles’ pe cen age
Table 2
Vehicle lee by ype in pe cen ages o EU bus manu ac u e s.
Bus
(Ca ego y
M3)
Be o e
2030
F om Janua y 1,
2030, o Decembe
31, 2034
F om Janua y 1,
2030, o Decembe
31, 2039
As
om
2040
Ze o-
emission
ehicles
0 % 90 % 100 % 100 %
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
2
Table 3
BFRP li e a u e e iew.
Au ho
(Re e ence)
Vehicle
ype
Objec i es Policy
Go
Conclusions
O hman
e al. [22]
BEB De elop ools
( eplacemen
ac o s, p edic ion
models) o es ima e
equi ed BEB lee
size o equi alen
se ice le el.
No Replacemen
ac o depends on
hea ing sys em &
season (highe in
win e ). ML
models p edic
lee size
accu a ely based
on dis ance, emp,
ba e y size.
F ieβ &
P e schy
[16]
BEB,
HFCB
Minimize LCC o
mixed- lee ZEB
sys em by
op imizing
echnology mix,
in as uc u e, and
schedules.
Con ex Mixed lee s
inancially
ou pe o m single-
ech solu ions.
Op imal mix
sensi i e o
ope a ional
cons ain s &
planning
assump ions.
Enaya i
e al. [23]
DB, BEB Find equilib ium
s a egies o PTS,
manu ac u e &
passenge choice
using game heo y
unde di e en go .
policies
Con ex Subsidies o
elec ic buses and
axes on diesel
ones a e he mos
e ec i e
go e nmen
measu es o
p omo e lee
elec i ica ion,
while ma ke -
based ools like
Cap & T ade a e
less e ec i e.
Public suppo is
d i en by
en i onmen al
conce n.
S asko &
Gao [19]
DB,
CNGB,
BEB,
HEB
Minimize long- e m
ope a ional cos s +
emission penal ies
by in eg a ing
pu chase, e o i &
ask assignmen
decisions.
No Long-ho izon
planning supe io
o sho -ho izon.
CNG can be cos -
e ec i e. Ca bon
p ice in luences
ech choice.
Ribei o &
Mendes
[20]
DB,
DHB,
CNGB
De elop & e alua e
a na ional (Po ugal)
bus eplacemen
scena io based on
age c i e ia o ull
deca boniza ion by
2034.
Con ex Full lee
eplacemen wi h
ZEVs by 2034 is
easible based on
age c i e ia.
Requi es
signi ican
in es men bu
g ea ly educes
a e age lee age.
Bakke
e al. [21]
Elec ic
and
Diesel
T ucks
Minimize o al cos s
o lee eplacemen
(pu chase, sal age,
ope a ion, in a.)
o e mul i-yea
ho izon.
No ETs can educe
o al cos s bu
equi e high
up on CAPEX
( ucks, cha ge s,
g id). Depo
cha ging key;
public cha ging
cos c i ical o
long-haul ET
iabili y.
Tang e al.
[24]
BEB Selec op imum EB
ype o single line
eplacemen by
analyzing ade-o
be ween LCC and
passenge wai ing
ime.
No T ade-o : La ge
EBs ha e lowe
LCC (ope a o
iew), small EBs
ha e lowe wai ing
ime (passenge
iew). Type
selec ion obus o
Table 3 (con inued)
Au ho
(Re e ence)
Vehicle
ype
Objec i es Policy
Go
Conclusions
line leng h & low
subsidies.
Lu e al.
[25]
DB, HEB,
BEB
E alua e li ecycle
economic &
en i onmen al
pe o mance o
al e na i e uel
buses in Eu ope,
conside ing clima e
& ene gy mix.
No Mixed lee s
(Hyb id +Elec ic)
can balance cos &
en i onmen
be e han ull
elec ic in some
Eu opean con ex s.
Seasonal ope a ion
adjus men s
bene icial.
Islam &
Lownes
[17]
DB, HEB,
BEB
Minimize LCC &
GHG emissions
simul aneously ia
op imized pa allel
lee eplacemen
schedule & mix.
No Op imized
eplacemen
educes LCC &
GHG. Op imal mix
depends on
cons ain s (e.g.,
79 % BEB/21 %
HEB ound cos -
op imal unde
elaxed
cons ain s).
A enali
e al. [18]
DB,
CNGB,
HEB,
BEB
E alua e lee
eplacemen
decisions unde
unce ain y using
Real Op ions o ind
op imal iming &
echnology,
maximizing cos
sa ings.
No RO shows
an icipa ing
eplacemen ( s.
end-o -li e) sa es
cos s (up o 10 %
TCO) by
le e aging
lexibili y unde
unce ain y. BEBs
become dominan
o e ime. Sho
con ac s hinde
op imal
in es men
wi hou
gua an ees.
This wo k DB,
CNGB,
BEB
Minimize CO
2
emissions and
o e all cos by
applying a BFRP
s a egy o each o
he p oblems in a
PTO in Se ille,
aking in o accoun
no only economic,
echnological, and
logis ical
cons ain s, bu also
EU legisla ion
applicable o PTO
and u ban buses
Yes The me hodology
enables cos o CO
2
ocused lee
op imiza ion using
eal Se ille da a.
Despi e BEB high
pu chase cos ,
labo ac o s
educe TCO
di e ences.
Emissions d op by
16.3 % wi h only a
6.7 % cos gap.
Accu a e ene gy
modeling and
in as uc u e
planning a e
c ucial o
e ec i e,
egula ion-
complian lee
enewal in u ban
se ings.
Vehicle ype
DB: Diesel bus; CNGB; CNG bus; HEB; Hyb id elec ic bus; DHB: Diesel hyb id bus;
HFCB: Hyd ogen Fuel Cell bus; BEB: Ba e y Elec ic Bus
Policy o go e nmen
Yes: Go e nmen policies a e explici ly in eg a ed in o he op imiza ion model as
o mal cons ain s, di ec ly in luencing he easible solu ion space
Con ex : Policy conside a ions a e acknowledged and in o m he o e all p oblem
se ing, bu a e no explici ly as cons ain s wi hin he op imiza ion amewo k
No: Go e nmen policies a e nei he conside ed in he o mula ion e e enced in he
con ex o he op imiza ion p oblem
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
3
clean and ze o-emission ehicles) di ec ly o a PTO in Se ille, a he
han ocusing on age-based c i e ia o a b oade na ional deca bon-
iza ion scena io. Bakke e al. [21] inco po a ed a de ailed analysis o
in as uc u e- ela ed decisions, such as he a ailabili y o depo and
public cha ging s a ions, in o cos minimiza ions amewo ks ha
include pu chase, sal age, and ope a ional cos s. In his s udy adop s a
simila cos s uc u e; howe e , i is uniquely g ounded in eal ope a-
ional da a om a Se ille PTO. This p o ides ac ual local da a, dis-
inguishing ou wo k om s udies ha migh ely on e e enced
in o ma ion om o he sou ces o in o m hei models. A comp ehensi e
compa ison be ween p io esea ch and he cu en s udy is delinea ed
in Table 3, whe e key li e a u e is syn hesized by compa ing objec i es,
ehicle ypes, policy in eg a ion (as o mal cons ain s, con ex ual ele-
men s, o absen ), and indings om each s udy.
While hese con ibu ions ha e g ea ly ad anced he ield, he
ansi ion o low-o ze o-emission lee s s ill p esen s majo challenges
o PTO [20], especially unde scena ios equi ing ull lee elec i ica-
ion. These challenges s em om dynamic ma ke condi ions, echnol-
ogy unce ain ies, and inc easingly s ingen EU di ec i e p omo ing
sus ainable u ban mobili y. Mo eo e , al hough a ious cos dimensions
ha e been s udied in isola ion, ew models simul aneously accoun o
egula o y compliance, eal-wo ld ope a ions, and he join e alua ion
o en i onmen al and economic pe o mance.
While in o med by s udies such as Ribei o & Mendes [20] ( ocusing
on CO
2
and cos minimiza ion, including capi al, main enance, and
ene gy expendi u e) and Bakke e al. [21] (inco po a ing pu chase,
sal age, and ope a ional cos s), he p esen esea ch o e s a dis inc
con ibu ion. We uniquely g ound ou analysis in a local con ex using
eal ope a ional da a om a PTO in Se ille, Spain. This s udy in oduces
an in eg a ed op imiza ion amewo k o he BFRP o he PTO, designed
o ill iden i ied esea ch gaps. A key ad ancemen o ou model is i s
explici inco po a ion o mul iple lee enewal s a egies ha a e
di ec ly cons ained by EU egula ions, a le el o egula o y in eg a ion
no consis en ly ound in exis ing app oaches.
The ollowing sec ions ou line he s uc u e o he pape : Sec ion 2
in oduces he BFRP p oblem desc ip ion and ma hema ical o mula-
ion. Sec ion 3de ines he cos s associa ed wi h he bus lee o in eg a e
hem in o he op imiza ion model. Sec ion 4p o ides da a on he spe-
ci ic case s udy ob ained om eal-wo ld ope a ional da a. Sec ion 5
p esen s he esul s o he op imiza ion model, discussing hem and
p o iding a sensi i i y analysis o a ious pa ame e s o alida e he
s udy. The conclusions a e p esen ed in Sec ion 6.
2. P oblem desc ip ion
In his sec ion, he BFRP is in oduced and ma hema ically o mu-
la ed. Fig. 1 shows he main s uc u e o he op imiza ion p oblem whe e
six main cos elemen s a e conside ed: pu chase cos , sal age e enue
(once he bus has eached sal age age, i is sold, making his e m a
sou ce o income), ene gy cos s (in e ms o diesel, CNG, o elec ici y),
main enance cos s, insu ance cos s, and d i e cos s. The p oblem has
been o mula ed wi h wo dis inc objec i es o be analyzed. One is o
minimize he discoun ed sum o all ope a ing cos s, and he o he is o
educe he o al amoun o ca bon dioxide emissions as much as
possible. Bo h objec i es a e add essed independen ly o e he planning
ho izon and a e subjec o echnical, company, and s anda d cons ain s.
In his ega d, he mos ele an aspec s a e compliance wi h EU s an-
da ds and budge limi a ions, assuming ha all inpu pa ame e s a e
known wi h ce ain y. The me hodology p esen ed in his wo k lies in
he use o eal, ope a ional da a a he han elying on gene ic as-
sump ions o li e a u e-based es ima es. Unlike many s udies ha base
hei cos analysis on heo e ical models o ex e nal sou ces, his s udy
de i es he cos s o all agen s in ol ed in he cu en ope a ion o he
PTO om ac ual ope a ional da a collec ed o e a ull calenda yea . In
addi ion, c i ical cos - ela ed in o ma ion was di ec ly p o ided by he
PTO, ensu ing ha he analysis e lec s he speci ic con ex and eali ies
o he lee ’s daily ope a ions. A gene al desc ip ion o he p oblem is
p o ided, ollowed by i s o mula ion as an in ege linea p og am.
Fig. 1. Main s uc u e o he op imiza ion BFRP.
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
4
Wi hin he scope o he echnologies a ailable, h ee di e en ele-
men s can be pu chased: buses, ba e ies, and ba e y cha ge s. Fo
buses, a ange o di e en bus ypes has been conside ed K ={1, …, m},
whe e K
E
, K
G
, and K
D
a e h ee di e en subse s o bus ypes ha a e,
espec i ely, powe ed by elec ici y (ba e ies), CNG, and diesel uel.
Addi ionally, o each p opulsion echnology, he e a e wo ypes o
buses: egula and a icula ed, so m =6. Hyd ogen buses powe ed by FC
ha e no been conside ed as an al e na i e p opulsion echnology o
buses. This is because EU legisla ion [10]can be ul illed wi h ba e y
elec ic buses, he cos o hyd ogen buses is almos double ha o elec ic
ones [26,27], and he bus pa king si e lacks in as uc u e o a
hyd ogen ueling s a ion, which would incu addi ional cos s.
Fo ba e ies, wo di e en ypes a e conside ed, di ec ly ela ed o
hei size: he low-capaci y ba e y is used o he egula elec ic bus,
while he high-capaci y ba e y is used o he a icula ed bus; in his
ega d le B ={1, …, }, whe e B
L
and B
H
a e he wo subse s o ba -
e ies o low and high capaci y, espec i ely, so =2. Fo he ba e y
cha ge s we conside a ange o cha ge ypes G ={1, …, n}, whe e G
L
and G
H
a e he wo subse s o cha ge o medium and high capaci y, so n
=2.
A planning ho izon T ={1, …,
F
} consis ing o
F
pe iods is
conside ed, wi h wo a ge pe iods,
G1
and
G2
, included in T a which
a leas P
G1
and P
G2
p opo ions should be ul illed, acco ding o he
schedule in Table 1. Clea ly,
G1
<
F
and
G2
<
F
, bu all pe iods >
G1
and >
G2
in he planning ho izon should mee he a ge s P
G1
and P
G2
,
espec i ely.
Rega ding bus ask assignmen , he ou es do no ha e any special
cha ac e is ics, which allows adop ing he same modeling s a egy as in
Re . [28]. This is due o wo easons: he i s one is a consequence o he
PTO schedule, in which any bus ype — whe he egula o a icula ed
and powe ed by ba e ies, diesel uel, o CNG — can ollow any ou e.
Bo h ypes o uels used o bus p opulsion, diesel and CNG, p oduce CO
2
locally and since he e a e no es ic ions in Se ille ega ding his issue,
any bus ype can ope a e on any ou e. The second eason is connec ed
o he ci y’s o og aphy; Se ille is a comple ely la ci y, and he e o e,
he e a e no speci ic ou es ha p esen di e en ene gy demands ( om
he pe spec i e o he ene gy equi ed o bus p opulsion o clima iza-
ion) o be conside ed. I Se ille had a eas wi h s eepe ou es compa ed
o la e ones, each speci ic ou e should be conside ed, o a leas
g ouped, o accoun o he impac on ene gy consump ion, as clea ly
explained in sec ion 4. F om he poin o iew o a ailable ene gy, he
PTO o ganizes he buses so ha e e y bus ype s a s i s ou e e e y day
wi h ull capaci y. This means ha gas anks a e comple ely illed wi h
CNG a 200 ba , he diesel ank is ull, and he ba e ies o egula o
a icula ed buses a e ully cha ged. Due o he na u e o he ci y o
Se ille, he bo le capaci y o he CNG buses, he ank capaci y o he
diesel buses, and he cha ging in as uc u e o he ba e y elec ic
buses allow e e y bus, i espec i e o he subse o bus ypes wi hin K,
see Table 4, o comple e i s ull day’s un (a ound 14 h pe day) wi hou
he need o echa ge ba e ies o e ill he anks o bo les. The e o e, i
is no necessa y o exp ess pe iodic demands in a mo e g anula manne
as in Re s. [29,30], because he e a e no compa ibili y conside a ions o
be aken in o accoun be ween he bus ype and he ope a ion hey will
pe o m.
The age o each bus and ba e y mus be conside ed in he model
because e e y echnology has i s own end-o -li e. This is no he case o
ba e y cha ge s, which a e assumed o ha e an in ini e li espan. Le he
se J
k
={0, 1, …,
k
+1} be de ined o con ain all possible ages o a bus
o ype k, wi h j ∈J
k
ep esen ing an age o j pe iods. The age j =
0 co esponds o a new bus and he age j =
k
+1 is he poin a which he
bus mus be sal aged. A he s a o he planning ho izon, he lee
consis s o a
j
k
buses o ype k and age j.
Fo ba e ies, le he se Y
B
={0, 1, …, z
B
+1} be de ined o con ain all
possible ages o a ba e y o ype B, wi h y ∈Y
B
ep esen ing an age o y
pe iods. The age y =0 co esponds o a new ba e y and he age y =
z
B
+1 is he poin a which he ba e y mus be sal aged. A he s a o
Table 4
Pa ame e and a iable de ini ions o he BFRP model.
Se s
BSe o ba e y ypes
B
H
Se o ba e ies o high size
B
L
Se o ba e ies o low size
GSe o ba e y cha ge s
G
H
Se o ba e y cha ge s o high capaci y
G
L
Se o ba e y cha ge s o low capaci y
J
K
Se o possible ages o a bus o ype K
KSe o bus ypes
K
DA
Se o diesel a icula ed buses
K
DS
Se o diesel egula buses
K
EA
Se o elec ic a icula ed buses
K
ES
Se o elec ic egula buses
K
GA
Se o CNG a icula ed buses
K
GS
Se o CNG egula buses
TSe o
F
pe iod in he planning ho izon
Y
S
Se o possible ages o a ba e y o ype B
Pa ame e s
a
j
k
Numbe o buses o ype k and age j in he lee a he s a o he planning
ho izon
CMinimum age equi ed o any bus pu chased o be sal aged
c
y
b
Numbe o ba e ies o ype b and age y a he s a o he planning ho izon
d
y
b
Sal age alue o a ba e y o ype b and age y e i ed a he s a o pe iod
E
DS
Emission ac o Kg CO
2
pe km o egula diesel bus
E
DA
Emission ac o Kg CO
2
pe km o a icula ed diesel bus
E
GS
Emission ac o Kg CO
2
pe km o egula CNG bus
E
GA
Emission ac o Kg CO
2
pe km o a icula ed CNG bus
Δ Maximum allowable ime o achie e a comple e cha ge o he ba e ies
k
Pu chase cos o bus ype k a he s a o pe iod
h
g
Numbe o cha ge s o ype g owned a he s a o he planning ho izon
H
Budge o pu chases o buses, ba e ies and ba e y cha ge s a he s a o
pe iod
i Annual in la ion a e
KMM Annual dis ance [km] a eled by each bus pe yea
L
H
Elec ic load capaci y o high-capaci y cha ge s
L
L
Elec ic load capaci y o low-capaci y cha ge s
M
H
Capaci y o la ge-sized ba e ies
M
L
Capaci y o small-sized ba e ies
N
A
Capaci y o a icula ed bus (maximum numbe o passenge s)
N
S
Capaci y o egula bus (maximum numbe o passenge s)
NN
Capaci y o he whole lee a he s a o pe iod
o
j
k
To al pe iodic ope a ion cos when a bus o ype k is o age j a he s a o
pe iod
P
G1
Minimal p opo ion o he lee o be pu chased o clean and ze o emission
ehicles om a ge pe iod G1
P
G2
Minimal p opo ion o he lee o be pu chased o clean and ze o emission
ehicles om a ge pe iod G2
p Annual discoun a e
q
g
Pu chase cos o ba e y cha ge ype g a he s a o pe iod
k
+1Age a which buses o ype k mus be sal aged
R
1
Minimum a io be ween egula and a icula ed buses a he s a o pe iod
R
2
Maximum a io be ween egula and a icula ed buses a he s a o pe iod
s
j
k
Sal age alue o a bus o ype k and age j e i ed a he s a o pe iod
G1
Ta ge pe iod G1 o he applica ion o cu en EU s anda d [10]
G2
Ta ge pe iod G2 o he applica ion o cu en EU s anda d [10]
w
b
Pu chase cos o ba e y ype b a he s a o pe iod
z
b
+1Age a which ba e y o ype b mus be sal aged
Decision a iables
u
g
Numbe o cha ge s o ype g pu chased a he s a o pe iod
ua
g
Numbe o a ailable cha ge s o ype g a he s a o pe iod
x
k
Numbe o buses o ype k pu chased a he beginning o pe iod
xs
j
k
Numbe o buses o ype k and age j sal aged a he beginning o pe iod
xa
j
k
Numbe o a ailable buses o ype k and age j a he beginning o pe iod
b
Numbe o ba e ies o ype b pu chased a he beginning o pe iod
s
y
b
Numbe o ba e ies o ype b and age y sal aged a he beginning o pe iod
a
y
b
Numbe o a ailable ba e ies o ype b and age y a he beginning o pe iod
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
5
he planning ho izon, he e a e c
y
B
ba e ies o ype B and age y.
Al hough age is no conside ed o ba e y cha ge s, a he s a o he
planning ho izon he e a e h
G
cha ge s o ype G.
Conside ing cos issues, o
j,
K
ep esen s he o al pe iodic ope a ing
cos when a bus o ype K is a age j a he s a o pe iod . These
ope a ing cos s include expenses o ene gy, main enance, pe sonnel
and insu ance and a e speci ic o each p opulsion echnology. Le
K
be
he pu chase cos o bus ype K a he s a o pe iod , conside ing ha
only new buses a e pu chased, al hough conside ing used buses o
leasing could be a iable al e na i e. Only K
E
and K
G
buses a e he e
conside ed in o de o educe bo h local and global pollu ion [31]. The
sal age alue o a bus o ype K and age j e i ed a he s a o pe iod is
s
j,
K
.
Le w
B
be he pu chase cos o ba e y ype B a he s a o pe iod ,
conside ing ha only new ba e ies a e pu chased. In he case o ba e y
elec ic buses, he cos o he bus does no include he cos o he ba e y,
which mus be conside ed sepa a ely. This modeling decision has been
made because he li espan o he ba e y is signi ican ly sho e han ha
o he elec ic bus. The sal age alue o a ba e y o ype B and age y
e i ed a he s a o pe iod is d
y
B
; since ba e ies can only be sal aged
a he end o hei use ul li e, y =z
B
+1.
Fo ba e y cha ge , le q
G
ep esen he pu chase cos o ba e y
cha ge ype G a he s a o pe iod . Since ba e y cha ge s a e
conside ed o ha e an in ini e li espan, no sal age alue is conside ed.
I is assumed ha he pa king a ea o ba e y elec ic buses has
su icien space o he ins alla ion o ba e y cha ge s, and he e o e
he e a e no es ic ions in his ega d. Addi ionally, because he elec ic
demand is ela i ely low compa ed o he o al ins alled elec ic powe
a he bus pa king si e, he e a e no ex a cos s o elec ici y con-
sump ion beyond he ac ual ene gy used.
A budge H
is a ailable a he s a o pe iod o pu chase o buses,
ba e ies and ba e y cha ge s, which can be inc eased by sal age e -
enues ea ned a he s a o . Howe e , he sal age alue o buses and
ba e ies is e y low compa ed o he acquisi ion cos , 15 % o pu chase
p ice [32]. Finally, le p be he pe iodic discoun a e used o conside
he ime- alue o money, being 1/(1 +p ) he co esponding one-pe iod
discoun ac o . All cash lows a e assumed o occu a he beginning o
each pe iod; he e o e, an amoun incu ed in pe iod will be discoun ed
by 1/(1 +p )
−1
. Finally, a cons an annual in la ion a e i has been
inco po a ed in o he model o he en i e analysis pe iod.
2.1. In ege linea p og amming model
The op imiza ion model is o mula ed as a de e minis ic he e oge-
neous lee eplacemen model, whe e all inpu pa ame e s a e known
wi h ce ain y. The decision a iables a e de ined in Table 4; all a e
in ege s, non-nega i e, and ep esen he numbe o each componen
pu chased (ba e ies, cha ge s, buses) o di e en ypes, he numbe o
sal aged componen s, and he numbe o a ailable componen s.
Two independen objec i e unc ions a e conside ed, wi h he
model’s cons ain s emaining he same o bo h. One o he objec i e
unc ions minimizes he o al discoun ed cos o e he planning pe iod,
including pu chase cos s, sal age e enues, and ope a ing cos s. The
pu chase cos a ies o each pe iod o buses, ba e ies, and cha ge s
o e he analysis pe iod. The objec i e unc ion is de ined by equa ion
(1), while he comple e se o equa ions ha comp ise his model in-
cludes equa ions (1), (3) and (4), …, (29).
Simila ly, he objec i e unc ion o minimizing he o al CO
2
emis-
sions o e he analysis pe iod is de ined by equa ion (2), wi h he co -
esponding model consis ing o equa ions (2)–(4), …, (29), whe e i is
assumed ha all buses co e he same dis ance (KMM) each yea . I is
wo h men ioning ha he elec ici y consumed by he PTO is ce i ied
g een, meaning ha 100 % o he ene gy used comes om enewable
sou ces. As a esul , he elec ici y used o cha ge he ba e ies is en i ely
ca bon- ee, meaning he e a e no CO
2
emissions om he ba e y
elec ic buses.
Objec i e unc ion o minimizing he o al exploi a ion cos
minimize ∑
∈T(1+i
1+p ) −1
∑
k∈K( k
xk
−∑
k+1
j=1
sk
j xsk
j +∑
k
j=0
ok
j xak
j )+
+∑
∈T(1+i
1+p ) −1
∑
b∈B(wb
b
−∑
k+1
j=1
db
y sb
y )+∑
∈T(1+i
1+p ) −1
∑
g∈G
qg
ug
(1)
Objec i e unc ion o minimizing he o al CO
2
emissions
minimize (∑
k∈KDS
xak
j EDS +∑
k∈KDA
xak
j EDA ∑
k∈KGS
xak
j EGS +∑
k∈KGA
xak
j EGA )KMM
∈T,j∈Jk { k+1}(2)
Cons ains
∑
k∈KG,KE
xk
≥PG1∑
k∈K
xk
∈T,∀ ≥ G1(3)
∑
k∈KG,KE
xk
≥PG2∑
k∈K
xk
∈T,∀ ≥ G2(4)
∑
k∈KE
xk
≥PG1∑
k∈K
xk
∈T,∀ ≥ G1(5)
∑
k∈KE
xk
≥PG2∑
k∈K
xk
∈T,∀ ≥ G2(6)
xk
=xak
j j=0,k∈K, ∈T {1}(7)
b
= ab
y y=0,b∈B, ∈T {1}(8)
xk
+ak
j=xak
j ,j=0,k∈K, =1 (9)
b
+cb
y= ab
y ,y=0,b∈B, =1 (10)
ug
+hg=uag
=1,g∈G(11)
uag
=uag
−1+ug
∈T {1},g∈G(12)
xak
j =xak
j−1, −1−xsk
j k∈K, ∈T {1},j∈Jk {0, k+1}(13)
ab
y = ab
y−1, −1− sb
y b∈B, ∈T {1},y∈Yb {0,zb+1}(14)
xsk
k+1, =xak
k, −1k∈K, ∈T {1},(15)
sb
zb+1, = ab
zb, −1b∈B, ∈T {1},(16)
xak
j =ak
j−xsk
j k∈K, =1,j∈Jk {0, k+1}(17)
ab
y =cb
y− sb
y b∈B, =1,y∈Yb {0,zb+1}(18)
∑
k∈K( k
xk
−∑
k+1
j=1
sk
j xsk
j )+∑
b∈B(wb
b
−∑
k+1
j=1
db
y sb
y )+∑
g∈G
qg
ug
≤H ∈T
(19)
ab
y ≥xak
j ∈T,b∈BL,k∈KES,y∈Yb {zb+1},j∈Jk { k+1}(20)
ab
y ≥xak
j ∈T,b∈BH,k∈KEA,y∈Yb {zb+1},j∈Jk { k+1}(21)
∑
k∈KES,KDS,KGS
xak
j NS+∑
k∈KEA,KDA,KGA
xak
j NA≥NN ∈T,j∈Jk { k+1}(22)
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
6
∑
k∈KES,KDS,KGS
xak
j ≥R1 ⋅∑
k∈KEA,KDA,KGA
xak
j ∈T,j∈Jk { k+1}(23)
∑
k∈KES,KDS,KGS
xak
j ≤R2 ⋅∑
k∈KEA,KDA,KGA
xak
j ∈T,j∈Jk { k+1}(24)
xsk
j =0k∈K, ∈T,j∈Jk {C+1,C+2,…, k+1}(25)
sb
y =0b∈B, ∈T,y∈Yb {zb+1}(26)
Δ (∑
g∈GL
uag
LL+∑
g∈GH
uag
LH)≥∑
b∈BL
ab
y ML
+∑
b∈BH
ab
y MH ∈T,b∈B,g∈G,y∈Yb {zb+1}(27)
uag
≥xak
j ∈T,g∈GL,k∈KES,j∈Jk { k+1}(28)
uag
≥xak
j ∈T,g∈GH,k∈KEA,j∈Jk { k+1}(29)
Cons ain s (3) o (6) exp ess he es ic ions imposed by he cu en
EU di ec i e [10], as gi en in Table 1. Al hough his s anda d pe mi s
he con inuous pu chase o diesel buses, a majo goal o public com-
panies is o educe local con amina ion. Since eplacing diesel buses
does no achie e his goal, he pu chase o new diesel buses is no
allowed.
Cons ain (7) s a es ha he numbe o a ailable buses o each ype
wi h age 0 is equal o he numbe o buses o he same ype pu chased a
he s a o pe iod . Res ic ion (8) s a es ha he numbe o a ailable
ba e ies o each ype wi h age 0 is equal o he numbe o ba e ies o
he same ype pu chased a he s a o pe iod . Cons ain (9) exp esses
ha he numbe o a ailable buses o age 0 in he i s pe iod o analysis
is equal o he numbe o pu chased buses plus he numbe o new buses
o he same ype acqui ed be o e he i s analysis pe iod. Res ic ion
(10) exp esses ha he numbe o a ailable ba e ies o age 0 in he i s
pe iod o analysis is equal o he numbe o pu chased ba e ies plus he
numbe o new ba e ies o he same ype acqui ed be o e he i s
analysis pe iod. Res ic ion (11) s a es ha he numbe o a ailable
cha ges in he i s pe iod o analysis is equal o he numbe o pu chased
cha ge s plus he numbe o new ba e y cha ge s o he same ype ac-
qui ed be o e he i s analysis pe iod. Res ic ion (12) s a es ha he
numbe o a ailable cha ge s o any ype o any yea >1 is equal o he
numbe o cha ge s o he same ype a ailable in he p e ious yea , plus
he cha ge s o he same ype pu chased a he beginning o yea .
Equa ion (13) s a es ha he numbe o a ailable buses o any ype and
age j a he beginning o yea is equal o he a ailable buses o he same
ype om he p e ious yea , one yea younge , minus he buses o he
same ype and age sal aged a he beginning o yea . Equa ion (14)
exp esses ha he numbe o a ailable ba e ies o any ype and age y a
he beginning o yea is equal o he a ailable ba e ies o he same ype
om he p e ious yea , one yea younge , minus he ba e ies o he
same ype and age sal aged a he beginning o yea . Cons ain (15)
s a es ha he numbe o buses o ype k ha ha e eached he maximum
a ailable age a he beginning o yea is equal o he numbe o
a ailable buses ha , in he p e ious yea , we e one yea away om
being sal aged. Cons ain (16) s a es ha he numbe o ba e ies o
ype b ha ha e eached he maximum a ailable age a he beginning o
yea is equal o he numbe o a ailable ba e ies ha , in he p e ious
yea , we e one yea away om being sal aged. Equa ion (17) s a es ha
he numbe o a ailable buses o any ype and age j in he i s yea o
analysis is equal o he a ailable buses o he same ype and age p e i-
ously a disposal, minus he numbe o sal aged buses o he same ype
and age a he beginning o yea . Equa ion (18) exp esses ha he
numbe o a ailable ba e ies o any ype and age y in he i s yea o
analysis is equal o he a ailable ba e ies o he same ype and age
p e iously a disposal, minus he numbe o sal aged ba e ies o he
same ype and age a he beginning o yea . Cons ain s (19) s a e ha
he amoun o unds a ailable o he pu chase o buses, ba e ies, and
cha ge s a he s a o a pe iod is he sum o he budge and sal age
e enues gene a ed a he s a o ha pe iod. The model could
accommoda e di e en annual budge amoun s i hose igu es we e
known wi h ce ain y; his is o g ea impo ance because, in he con ex
o u ban public companies, he budge can change due o poli ical
easons.
Res ic ion (20) es ablishes ha he numbe o a ailable ba e ies o
any age y and ype B
L
mus be equal o o g ea e han he numbe o
a ailable egula ba e y elec ic buses o any age j a he beginning o
he analysis yea . Res ic ion (21) es ablishes ha he numbe o
a ailable ba e ies o any age y and ype B
H
mus be equal o o g ea e
han he numbe o a ailable a icula ed ba e y elec ic buses o any age
j a he beginning o he analysis yea . This ela ionship be ween ba -
e y and bus ype is due o he ac ha i is no possible o in e change
di e en ba e y capaci ies; ha is, he ba e ies a e no modula .
Cons ain (22) s a es ha he sum o he capaci y o egula and
a icula ed buses o any ype and age mus be a leas equal o he
es ablished capaci y o he bus lee in each analysis pe iod. Inequali y
(23) s a es ha he a io o egula o a icula ed buses o any p opulsion
ca ego y and age mus be a leas g ea e han R
1
a he beginning o he
analysis pe iod. Inequali y (24) s a es ha he a io o egula o a ic-
ula ed buses o any p opulsion ca ego y and age mus be less han o
equal o R
2
a he beginning o he analysis pe iod.
Equali y (25) s a es ha any pu chased bus o any ype can only be
sal aged a e eaching a minimum age C, in acco dance wi h Spanish
equi emen s. Equali y (26) s a es ha any pu chased ba e y o any
ype can only be sal aged a e i has eached i s allowable ope a ional
li e.
Cons ain (27) es ablishes ha he cha ging capaci y o he ba e y
cha ge s du ing a ime in e al Δ , ypically less han 6 h, is su icien o
ully cha ge all he ba e ies, ega dless o whe he hey a e o low o
high capaci y. Res ic ion (28) s a es ha a leas is necessa y one low
capaci y cha ge o each egula elec ic bus and (29) s a es ha a leas
is necessa y one high capaci y cha ge o each a icula ed elec ic bus.
3. Use ul li e and cos s
3.1. P opulsion ba e y cos and sal aged alue
Acco ding o Bloombe g NEF’s annual ba e y p ice su ey [33],
p ices ha e allen in 2023. The p ice e olu ion is he esul o h ee
opposing o ces: he e olu ion in aw ma e ial and componen p ices,
he g ow h in p oduc ion capaci y, and expec ed demand, all o which
a e cons an ly changing. The e o e, ba e y p ices a e expec ed o e ol e
in he nea u u e wi h a nega i e slope o app oxima ely 8
€
/kWh pe
yea s a ing wi h a cons an p ice o 245
€
/kWh in Janua y 2024.
P opulsion ba e ies ha e a maximum ope a ional li e o 10 yea s, as
assu ed by he manu ac u e [34]. Once his limi is eached, he ba -
e ies mus be sal aged om use as p opulsion ene gy s o age. Howe e ,
EU egula ions conce ning ba e ies equi e o be designed in a way ha
allows o easy eco e y, euse, and ecycling [35]. In his ega d, i is
expec ed ha , in he sho e m, he e will be a seconda y ma ke o he
use o elec ic bus ba e ies in o he applica ions, and he e o e a sal age
alue mus be conside ed. The Na ional Renewable Ene gy Labo a o y
(NREL) om he U.S. Depa men o Ene gy has s udied he cos o
second-li e ba e ies in de ail. Acco ding o hei indings, a p ice o
second-li e ba e ies o a ound 15 % o he o iginal pu chasing cos can
be expec ed, which has been included in he analysis [32].
3.2. Bus cos and sal aged alue
Since diesel buses will no be pu chased, only he p ices o CNG and
ba e y elec ic buses a e conside ed. The e a e wo ypes o CNG buses
in he lee : egula and a icula ed. The a e age capi al cos o a new
M.A. Tagua Na a e e e al.
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7
uni is 375,000
€
and 460,000
€
, espec i ely. The cu en EU s anda d
[14], which manda es ha EU manu ac u e s educe he supply o his
ype o p opulsion echnology o no mo e han 10 % by 2034 (see
Table 2), will a ec he p ices o hese buses. Howe e , he e a e
cu en ly no p ojec ions ega ding hei p ice e olu ion, so a cons an
p ice is assumed o e he planning ho izon. Fo ba e y elec ic buses,
u u e p ice changes will p ima ily come om ba e y cos s, as he e is
li le oom o u he educe he p ice o o he ehicle componen s. The
capi al cos o a egula elec ic bus is 515,000
€
, and o an a icula ed
bus, i is 700,000
€
, bo h o which include he cos o he ba e ies. The
p ices come om Re . [36] and ha e been upda ed o m a e age alues
aken om a local su ey o manu ac u e s.
The ba e ies o he egula ba e y elec ic buses ha e a capaci y o
470 kWh, while hose o he a icula ed ba e y elec ic buses ha e a
capaci y o 720 kWh.
Buses powe ed by hyd ogen h ough FC o in e nal combus ion en-
gines ha e no been conside ed o h ee easons.
•The cos o hese buses is oughly 35 % highe han he p ice o an
elec ic bus [20].
•The cos o g een hyd ogen is app oxima ely wice ha o elec ici y
[37].
•Wi h ba e y elec ic buses, he EU s anda d [10] is ully me .
The maximum use ul li e o diesel and CNG buses is ixed: 22 yea s
o diesel buses and 19 yea s o CNG buses [38,39]. In he case o CNG
buses, his limi is imposed by he use ul li e o he comp essed na u al
gas anks. The sal age alue o bo h diesel and CNG buses is negligible
because, a e such a long ope a ional pe iod, he alue is almos null. In
his ega d, Henshe ’s esidual p ice es ima e o 15 % o he pu chase
cos o diesel/CNG buses [40] is no conside ed. Ins ead, a ixed sal age
e u n alue o
€
2000 pe bus has been assigned. Fo ba e y elec ic
buses, he si ua ion is di e en . Al hough he expec ed use ul li e is 20
yea s, he deg ada ion o componen s (excluding he ba e y) is ex-
pec ed o be lowe [31], esul ing in a sal age alue o
€
50,000 o
egula buses and
€
60,000 o a icula ed ones.
3.3. Main enance cos s
Main enance cos s e e o a ious bus componen s such as i es,
ools, ex e nal wo kshops, spa e pa s, con aine s, ba e ies (non-p o-
pulsion), al es and b ake wea . The main enance cos s o ba e y
elec ic buses a e expec ed o be lowe han hose o diesel o CNG
buses, excluding ba e y eplacemen cos s. Fo ins ance, ba e y elec ic
buses ha e a egene a i e b aking sys em, which educes b ake wea
and lowe s ene gy consump ion [41]. Addi ionally, he cooling sys em
o diesel o CNG buses equi es signi ican ly mo e main enance and
spa e pa s compa ed o ba e y elec ic buses, which expe ience much
lowe he mal loads.
The a e age main enance cos is known and is based on a PTO su ey
o he en i e cu en lee , as shown in Table 5. Howe e , main enance
da a p esen ed in echnical publica ions di e signi ican ly om cu en
Table 5
Yea ly a e age main enance cos o he en i e lee o 425 buses o all ypes.
Main enance cos s
€
/yea o he whole lee
Ti es 268,418
Ba e ies (no o elec ic p opulsion) 62,367
Accesso ies/spa e pa s 2,817,248
Tools 111,029
Cleaning, Con aine s, ecycle bins 142,880
Ex e nal bus wo kshop 165,340
∑3,567,282/425 =
€
8394 pe bus
Table 6
Comple e bus lee composi ion as o Janua y 1, 2025; he age o each bus and ba e y ype a e included in he i s column.
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
8
p o en da a. Fo example [41], epo s a main enance cos o 0.35
€
/km
o diesel buses and 0.18
€
/km o ba e y elec ic buses (excluding he
p opulsion ba e y). Fo he PTO o Se ille, his ansla es o an annual
main enance cos o
€
15,750 pe diesel bus (simila ly o CNG buses)
and
€
8100 pe elec ic bus, assuming an a e age o 45,000 km/yea pe
bus [42]. Wi h ba e y elec ic buses accoun ing o 7.8 % o he en i e
lee , as shown in Table 6, and he a e age main enance cos o he
en i e lee being
€
8394 pe bus pe yea , i is clea ha he es ima ed
main enance cos s o diesel and CNG buses a e excessi e. A simila
o e es ima ion o main enance cos s o diesel and CNG buses is also
ound in Re . [17]. Ne e heless, he a io o main enance cos s be ween
elec ic and diesel buses in Re s. [17,41] is in he ange o 0.35–0.55.
In his ega d, his wo k conside s he same global main enance cos s
p esen ed in Table 5 bu assumes a a io o 0.45 be ween elec ic and
diesel o CNG buses, which esul s in a inal cos o
€
0.19/km o each
diesel o CNG bus and
€
0.087/km o each elec ic bus.
3.4. Insu ance and d i e cos s
Insu ance cos s a e he same o e e y bus, ega dless o he p o-
pulsion sys em o size ( egula o a icula ed), and a e ixed a
€
6000 pe
bus pe yea . The cos pe d i e is
€
61,000 pe yea , which includes he
o al sala y plus social secu i y con ibu ions paid by he company o
each d i e . Wi h 1264 d i e s o 425 buses, his implies an a e age
a io o 2.97 d i e s pe bus. This a io will also apply o e e y new bus
pu chased.
3.5. Fuel and ene gy cos s
Diesel and CNG a e he uels used o powe diesel and CNG buses,
espec i ely. Al hough uel p ices can luc ua e, he PTO bene i s om a
la a e ha alls wi hin he scope o he subsidies i ecei es. Diesel is
p iced a
€
1.20 pe li e , while CNG is p iced a
€
57 pe MWh.
The cos o elec ici y o cha ging bus ba e ies is also a la a e, se
a
€
0.14 pe kWh. In any case, e e ence [43] p o ides an EU benchma k
o elec ici y p ices applicable o ehicle cha ging.
3.6. Ba e y cha ge cos and cha ging schedule
Two ypes o ba e y cha ge s a e used: as cha ge s wi h a powe o
100 kW and apid cha ge s wi h a powe o 150 kW, wi h co esponding
cos s o
€
60,000 and
€
80,000, espec i ely. A as cha ge can ully
cha ge a 300 kWh ba e y ( o egula ba e y elec ic buses) in less han
4 h, while a apid cha ge akes a ound 4 h o ully cha ge a 450 kWh
ba e y ( o a icula ed ba e y elec ic buses). The e o e, wi h he
app op ia e numbe o cha ge s, all o he ba e y elec ic buses can be
cha ged in no mo e han 4 h, which is wi hin he ime ha he buses a e
pa ked. Mo eo e , i has always been conside ed ha a egula elec ic
bus equi es a leas a as cha ge , while an a icula ed elec ic bus
equi es a leas a apid cha ge .
3.7. Ex e nal cos s
The EU has p o ided a comp ehensi e handbook o e alua ing
ex e nal cos s, which quan i ies he cos pe kilome e (
€
/km) o each
i em [44], applicable o EU coun ies as well as a g oup o non-EU
coun ies. This opic has also been discussed in Re . [45], bu he
impac o including hese cos s in he analysis is negligible, as he ocus
is on minimizing he o al lee ope a ing cos o o al CO
2
emissions
[45]. Fo his eason, ex e nal cos s ha e no been included in his
analysis.
3.8. Flee composi ion
Table 6 p esen s he comple e bus lee composi ion as o Janua y 1,
2025, wi h he age o each bus and ba e y ype included in he i s
column. These co espond o he se o ages J
k
and Y
s
om Table 4. The
numbe o ba e y cha ge s a ailable includes 10 low-powe uni s and
23 high-powe uni s.
4. Ene gy demand and CO
2
emissions
Conside ing all ene gy consume s o he elec ic bus, he ollowing
ela ionship applies:
˙
We
TOTAL =˙
We
p op +˙
We
clim +˙
We
ai comp +˙
We
aux +˙
We
eg (30)
Whe e.
•
˙
We
TOTAL is he o al elec ic powe p o ided by he bus ba e ies.
•
˙
We
p op is he elec ic powe demanded o p opulsion.
•
˙
We
clim is he elec ic powe demanded by he clima iza ion sys em.
•
˙
We
ai comp is elec ic powe demanded by he bus ai comp esso .
•
˙
We
aux is he elec ic powe demanded by auxilia y equipmen .
•
˙
We
eg is he elec ic powe due o he egene a i e b aking, always
nega i e.
The mos signi ican ene gy consump ion comes om p opulsion,
and he powe equi ed by a ehicle o his pu pose [46] is de ined by
he ollowing equa ion:
˙
Wp op
η
mech = [(mbus +mpas)(g sin(
α
)+g cos(
α
)+a)+0.5CdA
ρ
2+Θw
2
w]
(31)
Whe e.
•˙
Wp op p opulsi e powe p o ided by he engine (elec ic o he mal).
•m
bus
is he mass o he ehicle.
•m
pas
is he mass o he passenge s.
•g is he g a i a ional accele a ion.
•
α
is he e ain slope.
•C
d
is he ehicle’s ae odynamic d ag coe icien .
•A is he on al a ea o he ehicle.
•
ρ
is he ai densi y (a he ambien empe a u e and p essu e o he
loca ion).
•
is he olling esis ance coe icien .
• is he ehicle speed.
•a is he ehicle’s accele a ion.
•
η
mech is he mechanical e iciency be ween he engine (diesel/CNG/
elec ic) and he p opulsion wheels ha i is es ima ed as a cons an
alue o 0.95.
•Θw is he momen o ine ia o a wheel.
• 2
w is he wheel adius.
F om he analysis o he abo e exp ession, i can be seen ha he
powe demand is a unc ion o he cube o he ehicle’s speed, and
he e o e, a medium and high speeds, he shape and on al a ea o he
ehicle s ongly in luence his powe . Howe e , o buses ope a ing
s ic ly in u ban a eas, he a e age speeds a e e y low, wi h a com-
me cial speed [42] below 14 km/h. Consequen ly, he e m o (31)
ela ed o he ae odynamic d ag ca ies li le weigh compa ed o he
o he e ms. The e m in equa ion (31) ha depends on he slope o he
e ain is in luenced by he ci y’s opog aphy [47]. While he e is no
possible ac ion on his e m, i can a ec he o he s—p ima ily he e m
(m
bus
+m
pas
)—since i he slope is s eep, he powe ese e a ailable o
accele a ion dec eases. The e m
mainly depends on he cha ac e is-
ics o he oad su ace and he i es and emains cons an o a ehicle
whose i es a e kep in good condi ion and p ope ly in la ed. Addi-
ionally, he momen o ine ia e m is e y small in compa ison wi h he
o he pa ame e s and can be neglec ed, as i ep esen only a minimal
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
9
would be equi ed, which would educe he alidi y o he model’s e-
sul s. Mo eo e , he model is designed o guide immedia e decisions
based on cu en ly a ailable in o ma ion and o ensu e compliance wi h
he EU s anda d. Addi ionally, he model can be e- un i he e is a
change in he EU s anda ds du ing he planning pe iod. Fu he mo e,
eme ging echnologies, such as FC buses o hyd ogen-powe ed in e nal
combus ion engines (H
2
ICE), can be in eg a ed in o he model as soon as
hey become comme cially a ailable and demons a e clea cos
ad an ages.
Gi en he da a, conside a ions, and pa ame e s om he p e ious
sec ions, he p oblem now becomes de e mining he decision a iables
lis ed in Table 4 acco ding o he cons ain s p o ided by equa ion (3)
h ough (29) o each o he 10 yea s o he analysis, in such a way ha
he o e all cos is minimized gi en by equa ion (1).
Fig. 5 shows he o al ope a ional cos and annual CO
2
emissions,
including all he ac o s discussed in Sec ions 3 and 4, o each yea o
he op imal solu ion, assuming a cons an maximum allowable budge
H
o
€
16.5 million. I is wo h no ing ha no easible solu ion exis s o
H
below
€
16.5 million. This indica es ha he EU places signi ican
economic p essu e on he PTO; i i had no pu chased he ba e y
elec ic buses lis ed in Table 6 p io o Janua y 1, 2024, i may no be
able o comply wi h he EU s anda d. I is wo h no ing ha he op i-
miza ion p ocedu e de ined unde his s a egy does no explici ly a ge
CO
2
emissions educ ion as an objec i e. Consequen ly, he dec ease in
CO
2
emissions obse ed in Fig. 5 is solely a esul o compliance wi h he
EU s anda d, a he han any delibe a e e o o minimize en i on-
men al impac .
By examining he e olu ion o global cos s o e he planning pe iod,
as shown in Fig. 5, i becomes e iden ha cos s expe ience a d as ic
educ ion s a ing in 2030, ollowed by an almos la end up o 2033,
when egula elec ic and CNG buses a e acqui ed as i can be app eci-
a ed in Fig. 6a. Looking a Fig. 7, which shows he pu chases o ba e ies
and cha ge s, due o he sho use ul li e o ba e ies, a la ge numbe o
hem need o be pu chased s a ing in 2032, al hough hese cos s a e low
compa ed o ope a ional cos s. The e o e, om 2031 onwa d, he p i-
ma y d i e o o al cos e olu ion is ope a ional expendi u e. Howe e ,
a no able cos inc ease occu s in 2033, due o he p ocu emen o 15
CNG buses and 8 ba e y elec ic buses, all o which a e egula uni s, as
can be seen in Fig. 6a. Wi h his s a egy, by 2029, he pe cen age o
clean ehicles o he lee eaches 95 %, and he sha e o ze o-emission
ehicles exceeds 17 %. As a esul o he inc ease in ba e y elec ic
buses, he equi ed elec ic powe ises om 6.2 MW in 2025 o 12 MW
by 2029, eaching a peak o 12.9 MW in 2033. This inc ease in powe
demand is ela i ely small and can be accommoda ed by he ins alled
capaci y a he PTO acili ies.
Since diesel buses a e no longe pe mi ed o new pu chases, he
numbe o bo h s anda d and a icula ed diesel uni s g adually dec eases
as hey each he end o hei se ice li e, as illus a ed in Fig. 6a. The
a io o a icula ed o s anda d buses is main ained a 40 % each yea ,
e lec ing he ope a ional limi cu en ly se by he PTO. This cons ain
is inco po a ed in o he model as inequali ies (23) and (24) (see Sec ion
2.1). Despi e he highe uni cos o a icula ed buses in each ca ego y,
his a io emains he mos cos -e ec i e con igu a ion due o he
associa ed educ ions in d i e - ela ed ope a ional cos s. The main
eason o his esul is he high d i e - ela ed cos s, wi h a d i e - o-bus
a io o 2.97, as discussed in Sec ion 3. In his con ex , a icula ed
sal aged diesel buses a e eplaced by a icula ed CNG buses o main ain
cos -e iciency. Addi ionally, he numbe o ba e y elec ic buses pu -
chased is kep a he minimum equi ed o sa is y he cons ain s se by
equa ions (3)–(6). Al hough ba e y elec ic buses o e lowe main e-
nance and ene gy cos s compa ed o CNG al e na i es, inc easing he
sha e o ze o-emission ehicles beyond he minimum manda ed by he
EU s anda d [10] is no a cos -e ec i e s a egy, p ima ily due o he
highe capi al in es men equi ed o elec ic ehicles, ba e ies, and
cha ging in as uc u e.
Mo eo e , he pu chase o new ba e y elec ic buses imposes an
addi ional elec ic powe load on he PTO, which e ol es annually as
shown in Fig. 8. In his igu e, i is assumed ha all he ba e y elec ic
buses a e a ailable o cha ge hei ba e ies simul aneously. I a di e en
cha ging schedule we e implemen ed o educe cha ging simul anei y,
he equi ed elec ic powe could be educed.
5.2. Sensi i i y analysis
The pu pose o he sensi i i y analysis is o accoun o u u e a i-
a ions in he model ou pu s due o unexpec ed changes in he model
pa ame e s. Gi en he cu en global economic and geopoli ical si ua-
ion, a educ ion in he cos s o ba e ies, ba e y elec ic buses, elec-
ici y, diesel, and CNG is expec ed in he medium e m, hough in an
unp edic able manne and he e o e i has no been included. Addi-
ionally, in la ion is expec ed o dec ease smoo hly in he sho e m, bu
i canno be p edic ed om he middle o he analysis pe iod onwa ds. In
his con ex , independen changes in he allowed a io be ween a icu-
la ed and egula buses a e conside ed. Inc easing he a io ange
Fig. 9. Annual global cos and CO
2
emissions o he minimum CO
2
emissions s a egy o e he planning pe iod.
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
16
be ween a icula ed and egula buses o 0.3–0.5 educes he global cos
om 905.7 M
€
o 881.2 M
€
, a 2.7 % educ ion. The numbe o a icu-
la ed CNG buses ises o 158 uni s by 2029, compa ed o 128 uni s in he
p e ious solu ion (see Fig. 5b). The o al numbe o a icula ed buses
inc eases o 201 due o he pu chase o CNG a icula ed buses ( he e is
no pu chase o a icula ed ba e y elec ic buses), educing he lee a
he end o he pe iod om 415 o 401.
Fu he inc easing he a io ange o 0.3–0.6 (see R
1
-R
2
in Table 4)
educes he global cos o 863.1 M
€
, a 4.7 % educ ion, wi h he numbe
o a icula ed buses inc easing o 233 uni s by 2030. In his scena io, he
numbe o a icula ed ba e y elec ic buses eaches 60 uni s by 2029,
while in he base solu ion he e was no change in he numbe o uni s.
This inc ease in a icula ed ba e y elec ic buses esul s in a educ ion
in CO
2
emissions, om 299.2 Mkg in he base case o 287.9 Mkg in he
new a io, a educ ion o 3.8 %. Howe e , he equi ed elec ical powe
o cha ging ba e y elec ic buses has inc eased om 13 o 14 MW, a
7.7 % inc ease.
5.3. Shi ing he op imiza ion ocus: CO
2
minimiza ion
Based on he da a, conside a ions, and pa ame e s ou lined in he
p e ious sec ions, he ask now is o de e mine he decision a iables
lis ed in Table 4, subjec o he cons ain s de ined by equa ion (3)
h ough (29) o each o he 10 yea s o analysis, in a way ha minimizes
he o e all CO
2
emissions as desc ibed by equa ion (2).
Fig. 9 p esen s he esul s in e ms o global cos and CO
2
emissions.
Compa ed o Fig. 5, his solu ion shows a sligh ly highe global cos o
€
967.5 million (an inc ease o 6.6 %) and CO
2
emissions o 254.0 Mkg,
ep esen ing a signi ican educ ion o 16.3 %. In Fig. 9, he cos de-
c eases mo e p og essi ely han in Fig. 5, while emissions expe ience a
sha p educ ion s a ing in 2029, d i en by he pu chase o egula
ba e y elec ic buses beginning in 2030, as illus a ed in Fig. 10. The
cos o he equi ed elec ic acili ies is excluded om he analysis, as
he e a e nume ous easible solu ions o he cha ging schedule ha
could signi ican ly educe he powe demand.
Fig. 10. Op imum solu ion minimizing CO
2
emissions pe each yea o he planning pe iod; a) numbe o pu chased buses, b) numbe o a ailable buses.
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
17
I is su p ising ha he inc ease in cos is no p opo ional o he
dec ease in CO
2
emissions, al hough he cos o he ba e ies mus also
include he cos o he cha ge s. This is due o he ac ha he o e all
cos o he buses is domina ed by d i e cos s, as each bus equi es nea ly
h ee d i e s o p o ide ull se ice. The inc ease in ba e y elec ic
buses necessi a es he ins alla ion o mo e ba e y cha ge s, and conse-
quen ly, he maximum ins alled elec ical powe a he PTO mus be
inc eased om 13 MW ( he op imum solu ion o minimum global cos )
o 30 MW, mo e han wice, as indica ed by he esul s in Fig. 11. In his
igu e, i is assumed ha all ba e y elec ic buses a e a ailable o cha ge
hei ba e ies simul aneously. I a di e en cha ging schedule we e
implemen ed o educe cha ging simul anei y, he equi ed elec ic
powe could be educed.
6. Conclusions
The p oposed me hodology de e mines he numbe o buses o each
ype ha need o be pu chased o ei he minimize o al ope a ing cos s
o educe CO
2
emissions while consis en ly mee ing EU s anda ds and
PTO equi emen s, aking in o accoun he exis ing lee composi ion a
he s a o he analysis. I also calcula es he equi ed elec ical ins alled
powe , p o iding aluable in o ma ion o he PTO o adjus he powe
capaci y in he pa king a ea. The main s eng h o his wo k lies in he
implemen a ion o a me hodology based on he use o de ailed, eal-
wo ld da a om he cu en lee , pa icula ly h ough he measu e-
men o all ele an elec ic ene gy consump ion pa ame e s in e ms o
powe . In his ega d, all ope a ional da a we e ob ained om he
CANBUS, which p o ides he ins an aneous elec ic powe o he a ious
ene gy-consuming componen s o he buses.
The compa ison be ween he wo op imiza ion s a egies e eals a
small cos inc ease—below 6.7 %—when CO
2
emissions a e minimized,
bu a signi ican educ ion in o al CO
2
emissions o 16.3 %. This solu-
ion, he e o e, makes a g ea e con ibu ion o he deca boniza ion o
he ci y o Se ille. Ne e heless, o comply wi h EU s anda ds, a mini-
mum annual budge o
€
16.5 million o pu chasing buses, ba e ies and
cha ge s is equi ed, which places signi ican p essu e on he PTO.
Despi e he signi ican cos di e ence be ween CNG and ba e y
elec ic buses—app oxima ely 40 % highe o s anda d buses and o e
50 % o a icula ed buses— he o e all cos di e ence be ween he wo
op imiza ion s a egies emains ela i ely small. This can be a ibu ed
o wo key ac o s.
•The high d i e - o-bus a io, app oxima ely 2.9
•The subs an ial sha e o d i e sala ies in he o al ope a ing cos s
These wo ac o s help mi iga e he inancial impac o acqui ing
mo e expensi e ba e y elec ic buses. Fu he mo e, inc easing he
p opo ion o a icula ed buses in he lee leads o lowe o e all cos s, as
ewe d i e s a e equi ed o anspo he same numbe o passen-
ge s— hus educing he o al labo cos .
The me hodology used o es ima e speci ic ene gy consump ion [kJ/
km] is pa icula ly app op ia e, as i allows he model o be cus omized
o he speci ic condi ions o he ci y o Se ille, a he han elying on
gene alized a e age alues om exis ing li e a u e. Using s anda d ig-
u es om o he s udies could esul in op imiza ion ou comes ha
signi ican ly de ia e om eali y. In his s udy, no able di e -
ences—app oxima ely 20 %—we e obse ed be ween he ene gy con-
sump ion measu ed di ec ly om Se ille’s lee ( o bo h s anda d and
a icula ed buses) and he alues commonly epo ed in he li e a u e.
These indings unde sco e he impo ance o using localized, eal-wo ld
da a o ensu e he accu acy and eliabili y o he op imiza ion p ocess.
Rega ding speci ic CO
2
emissions [kgCO
2
/km], i is wo h no ing
ha his alue is highe o CNG buses compa ed o diesel buses, despi e
he ac ha he kgCO
2
/MJ o na u al gas is lowe han ha o diesel
uel. This esul is explained by he highe ene gy consump ion o CNG
buses, which is due o he echnical design o CNG engines o powe
con ol. Fac o s such as a lowe comp ession a io compa ed o diesel
engines, a uel-ai s oichiome ic a io close o one, and a high pumping
loop a pa load—whe e hese buses ypically ope a e—con ibu e o
his inc eased consump ion. As he demanded powe dec eases, powe
losses inc ease, leading o lowe e iciency. I should also be no ed ha
he a e age demanded powe gene ally does no exceed 50 % o he
engine’s maximum powe .
Fu u e esea ch should ocus on inco po a ing he equi ed ins alled
elec ic powe o ba e y cha ging in o he op imiza ion model. This
aspec in oduces wo signi ican limi a ions. Fi s , he e is he inc eased
ins alla ion cos associa ed wi h upg ading in as uc u e o suppo
highe powe demands. Second, he e is he physical space equi emen
needed o accommoda e he necessa y cha ging acili ies. Ul ima ely,
bo h ac o s con ibu e o a highe o al cos in elec ic bus-based solu-
ions and will he e o e in luence and cons ain he ou comes o u u e
op imiza ion s a egies.
CRediT au ho ship con ibu ion s a emen
M.A. Tagua Na a e e: W i ing – e iew & edi ing, W i ing –
o iginal d a , Visualiza ion, Valida ion, So wa e, In es iga ion, Fo mal
analysis, Da a cu a ion, Concep ualiza ion. J. Se ano Reyes: W i ing –
e iew & edi ing, Valida ion, Supe ision. J.A. V´
elez Godi˜
no: W i ing –
e iew & edi ing, Valida ion, Fo mal analysis. F.J. Jim´
enez-Espada o
Aguila : W i ing – e iew & edi ing, Visualiza ion, Valida ion, Supe -
ision, Me hodology, Fo mal analysis, Da a cu a ion, Concep ualiza ion.
Decla a ion o compe ing in e es
The au ho s decla e he ollowing inancial in e es s/pe sonal e-
la ionships which may be conside ed as po en ial compe ing in e es s:
Miguel A. Tagua Na a e e epo s adminis a i e suppo was p o ided
by Uni e si y o Se ille. Miguel A. Tagua Na a e e epo s a ela ion-
ship wi h Uni e si y o Se ille ha includes: employmen . Collabo a ion
ag eemen be ween he Uni e si y o Se ille and T anspo es U banos de
Se illa S.A.M. I he e a e o he au ho s, hey decla e ha hey ha e no
known compe ing inancial in e es s o pe sonal ela ionships ha could
ha e appea ed o in luence he wo k epo ed in his pape .
Acknowledgemen s
We would like o exp ess ou since e g a i ude o TUSSAM o
Fig. 11. Annual maximum elec ic powe demand o he PTO in he minimum
CO
2
emission scena io.
M.A. Tagua Na a e e e al.
Ene gy 332 (2025) 137025
18
g an ing us access o he da a gene a ed by hei buses. This aluable
in o ma ion has been essen ial o ou analysis and has signi ican ly
con ibu ed o he de elopmen o his s udy. We uly app ecia e hei
collabo a ion and suppo , which ha e been ins umen al in ad ancing
ou esea ch.
Da a a ailabili y
The da a ha has been used is con iden ial.
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