Seite - 89 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 86 theireconomiccompetitiveness. For that reason, citiesaroundtheworldareworriedaboutdesigning sustainableyetefficientwaysofdoingfreightdeliveriesinurbanareas[15]. InEuropeandUSA,around 80%ofthepopulationlives inurbanareasalready. Sinceurbanareasusuallycontain largepopulations, extensivecommercial establishments, andan increasingdemandofservicesandcommodities, there is aneedto increase the frequencyofurbandeliveries,whichrequiresan intensiveuseof theexisting infrastructure. According to theUS Federal HighwayAdministration, the total vehiclemiles of travel increased 21% in the urban areas between 1996 and 2006. In fact, according to Feng and Figliozzi [16], theproportionof freight vehicles crossingurbanzones also increased from4.8% to 5.2%. As discussed before, freight distribution in densly populated cities are related to negative transportation externalities, such as congestion, pollution (both gas emissions andnoise), energy inefficiencies, decreasing road safety, infrastructures degradation, lack of roadway capacity and parkingspace,worsebreathingconditions, etc.AspointedoutbyRussoandComi[17],urbanfreight vehiclesaccount forabout6%–18%of the totalurbantravel, forabout19%of theenergyuse,andfor about21%of theCO2pollution. Someof the typicalpollutants inurbandistrictsare the following[18]: (i)mono-nitrogenoxides, whichareproducedbythecombustionof fossil fuelsandcontribute togeneratesmogandacidrain; (ii) sulfuroxides; (iii) carbonmonoxide; (iv)particulatematter;and(v)volatileorganiccompounds. All thepreviousgaseshavenegative effects onpeople’s health, asdiscussed inBernard et al. [19]. As a consequence, there is a strong impulse at international, national, and local levels tomitigate thembyswitchingtozeroemissions technologies, theshift toEVsbeingoneof themostpromising policies.Also, this shift canbeagoodsolutiontorelieveotherproblemsrelatedtourbandistribution. Thus, for instance, Nüesch et al. [20] propose amethod tominimize the fuel consumption using hybridEVswhile tracking agiven reference trajectory for both emissions and thebattery state of charge. Similarly,Collin et al. [21]designagenericmethodologyto incorporateenvironmentaland battery-relatedconstraints intoon-lineenergymanagement strategies fordifferent typesofhybrid EVs, while Chen et al. [22] introduce an energymanagement approach tominimize total energy costassociatedwith theuseofhybridEVs. Finally, in thecontextofurbantransportationnetworks, Hwang et al. [23] propose a stochasticmodel tominimize the expected total cost of freight truck activities,where thesecosts includetotaldelivery time,different typesofemissions,andapenalty for lateorearlyarrival. Urbantransportusually involvesvehiclesoperatingwith lowloading levels, thusresulting in anon-efficientuseofoil-basedenergy.Moreover,urbandeliveryvanshavea lowaveragedriving speed, andelectric enginesaremoreefficientat lowspeeds. Likewise, the routes covered inurban distributionarequitesimilar fromonedaytoanother,whichcanfacilitate thedesignofstablepolicies forbattery rechargingorbattery swapping. It is clear then that a shift froma fossil fuelfleet toan electric-poweredfleet isnecessary inorder toreducepollutantemissions incities.AconversiontoEVs wouldimplytheconjointdevelopmentof transportationandpowergenerationsectors,andwould shiftGHGemissions fromconventionalvehicle tailpipes tobigelectricpowerplants. Ontheonehand,EVsusingelectricity fromthepublicgridwillplayacritical role inreducing GHGemissions and inmitigatingnegative transport externalities. Nevertheless, these reductions in emissionswill be only possiblewithin a scenario of low-carbon electricity production, i.e., the replacementof ICEVsbyEVs isonlyreasonable if theelectricitygenerationhasa lowlevelofcarbon production.Otherwise,onepollutant technologywouldbeswappedbyanotherpollutant technology (maybe less pollutant, but not really sustainable either). Additionally, EVs are ideal tomake the distributionof lightproductswitha lowemissionpollutants impact incitycenters. That fact isdue to: (i) the lackofgasreleases inEVs;and(ii) theusuallysmall sizeofEVs,whichallowsthemtoeasily accesshighcongestedstreetswith limitedparkingspace.ManycitiesallowEVstouseparkingspaces for free. Thus,EVsareconstrainedtoa lesserdegreebytheexistenceofcongestionor lackofparking areas thanICEVs. This implies that thewalkingdistancescoveredbythedriversofEVsareusually shorter than the onesperformedby ICEVsdrivers [24]. In fact, it is common to see conventional 89