Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Carsharingthroughthedataanalysislens
ChiaraBoldrini*,RaffaeleBruno,andMohamedHaitam LaarabiIIT-CNR,Italy
Carsharing• ShareduseofafleetofcarsbyCSmembers• Obstaclesforcoordinationremovedbytechnology
• CSexplosioninthelast15years• 3maincarsharingmodes
• Two-way:tripsstartandendatthesameCSstation• One-way:tripsmayendatanyCSstation• Freefloating:on-streetparkinganywherewithinthegeofence
1891
Invention of taximeter
1916 1948 1970
Joe Saunder decided to lend out his Ford Model T to local and visiting businessmen
Sefage started its service in Zürich
Witkar(technology-based) in Amsterdam
2000
Zipcar
2008
Car2go(free-floating)
explosion2011
AutolibDriveNow
2013
Enjoy
Motivationbehindthiswork
• OpenproblemsinCSresearch• Vehicleredistribution• Cleaningandmaintenance• Infrastructureplanning
• Carsharingisaweaksignalinthecitylandscape• thefractionofpeoplerelyingoncarsharingfortheirdailytripsisrapidlyincreasing
butitisstillintheorderofsingledigitpercentagepointsinthebestcases.
• Carsharinghasbeenmostlystudiedthroughsurveys anddirectinterviewswithitsmembers.
• Carsharingistypicallynotaccountedforinhouseholdstraveldiariesperiodicallycollectedbycityadministrations.
• Candataminingofferhelpfulinsights?
Thedataset
• AvailabilityovertimeofCSvehicles in10Europeancitiesforoneofthemajorfree-floating carsharingoperators.
• Observationperiod:• May17,2015andJune30,2015(for9cities)• March11,2016toMay12,2016.
• Datacollectedevery1minute usingtheavailablepublicAPI,whichyieldsresponsesintheformofJSONfiles.
• Datacleaning:• technicalproblemsonthebookingwebsite->corrupted
entriesdiscarded• faultyGPSsystems->coordinatesthataremanifestlyinvalid
(e.g.,carsavailableindifferentcountries)havebeendiscarded.
• DatapreprocessingandanalysishasbeencarriedoutinR.
Electricvehiclesonly
Datasetlimitations
• Movementsareinferred fromcarsdisappearingontheCSmap• MovementfromAtoB=acardisappearsfromlocationAtolaterreappearatlocationB
• Noexplicitwayfordistinguishingbetweenregularcustomertripsandmaintenancetrips
• Nodirectinformationaboutthetrajectory followedbythesharedvehicle
• WehavequeriedGoogleMapsaskingfordirectionsandexpectedtraveltimebetweenthesourceanddestinationcoordinatesofeachtrip
• Estimatedthetravelleddistanceusingreal-lifeaverageconsumptionextractedfromhttps://www.spritmonitor.de/en/
<vehicle_id, GPS_coords, engine_type, fuel_level, interior_exterior_state>
Themodeshareinthe10cities
• 3classesofcities:oneinwhichmotorised modesdominate,oneinwhichpublictransport(andhencewalking)aremoreimportant,andoneinwhichpeoplemoveprevalentlybybike
Source:Eurostat’sCityUrbanAuditdatabase
Vehicleutilizationrate
• thenumberofdailytrips pervehicle• indexthatisoftenusedasameasureofcarsharingsuccess,asitcapturesshortandfrequenttrips
Service was in fact shutdown
DoesmodalsplitcorrelatewithsuccessfulCS?
• Bike(Pearsonr=−0.34)
• Publictransport(r=0.22)
• Walkingandmotorcycle(r=0.06andr=0.0051)
• Cars(r=0.09).
Dowereallyneedrelocation?
• Wedividetheoperationalareaincellswithsidelength500m
• Weobservehowthe%ofemptycellsvariesovertime
There are always a lot of empty zones in
the cities!
The CS in City#9 had opened just a few weeks before our
data collection, and its service hadn’t yet stabilized.
Therelocationpotential– part1
Even in the best
case, vehicles remain parked most of the time!
• #emptycells +#idlevehicles =strongconcentrationofvehiclesincertainareas
• Thisisgoodnewsfortheresearchonvehicleredistribution:theoperatorcanindeedexploitalargenumberofvehiclesthatarenotusedmostofthetime…
Therelocationpotential– part2
• …provideditispossibletoaccuratelypredictwherecarswillberequestedinthenearfuture
• WemeasureCELL REGULARITY intermsofthenumberofpickupeventsobservedwithinthecellduringworkingdays.
• Inordertomeasurehowmuchthenumberofpickupsvariesacrosstheobservationperiodweusethetechniquedescribedin[1].
• Wedivideeachdayintobins• ForeachcellN,wecomputethe#oftripsstartingatNforeachbin(1,…,n)ofdayi:
• Wecomputetheaccumulatedvarianceduringthel daysofobservationperiodas:
[1]Zhong,Chen,etal."Variabilityinregularity:MiningtemporalmobilitypatternsinLondon,SingaporeandBeijingusingsmart-carddata." PloS one 11.2(2016):e0149222.[1]Zhong,Chen,etal."Variabilityinregularity:MiningtemporalmobilitypatternsinLondon,SingaporeandBeijingusingsmart-carddata." PloS one 11.2(2016):e0149222.
Squared correlation
the vast majority of cells has an extremely predictable behaviour, with limited variability
the number of outliers is significant, and it should be taken into account when designing supply models for car sharing services
(e.g., unpredictable cells should not be taken into account in the redistribution process).
Howmanydifferentcellusages?• Weusedthefollowingtechniques:
• Wediscretize time into bins with a duration of 10 minutes• We compute the average occupancy (# available vehicles) in each bin across
the observation period• We normalize by the average daily availability in each cell• DynamicTimeWarping:measureshow“close”twotimeseriesare
• Takesintoaccountminorshiftsintimethatcanbeoftenseenintimeseries• PAMClustering:createsk groupsofsimilarstationsbasedontheDTWdistance
• SilhouetteMethod:forselectingthemostinformativek
• The optimal number of clusters in all cities ranges from 2 to 4.
• The fourth cluster, when present, is a very special cluster, composed of just one cell (overlapping with the airportzone)
Bell shaped: above average availability at night and below average availability
during the day
Inverted bell: above average availability at night and below average availability during the day
Flat: no significant difference in usage is detected over the whole day
Business/commercial areas
Residential areas
Mixed usage
Identifyingpotentialserviceareas
• Cleaningandmaintenance isacriticaloperationalaspectinCS
• thecarsharingworkforceisdispatchedtocollectvehiclesthatareinneedofeither
• Movingworkersaroundisexpensive,andmoreefficientsolutionscouldbefoundbasedonthevehicleusageinthecity
• POTENTIAL SERVICE AREA:alocationvehiclepassbywithveryhighprobabilitywithinapredefinedtimewindow
• workshopscouldbedeployedinthisarea,andthiswouldmakecleaningandmaintenanceoperationsmuchmoreefficient
Ourapproach
• WedefineareferencetimewindowW,correspondingtotheacceptedtimebeforetakingoutavehicleformaintenance
• Then,foreachcell,wecountthenumberofdistinctvehiclesseenbythecellsduringW
• Weassumethatathresholdof50%vehicleswouldbeacceptableforthecarsharingoperatortojustifytheopeningofaworkshopinthearea
Only 2 out of 10 when W=15 days
• In both cases, the service area would be located at the airport!
Only 5 cities out of 10 are able to satisfy this requirement when W=30 days
Conclusions
• Carsharinghasn’tbeenmuchdata-drivensofar,butdataanalysiscanofferimportantinsightsforthemanagementofacarsharingsystem
• Inthisworkwehaveprovidedsomeexamples,highlightingtheirimpactonCSoperations:
• Wehaveshowntheimportanceofvehicleutilizationrate andhowitcorrelateswithmodalsharesinthecities
• Wehavehighlightedthehugepotentialforvehiclerelocationduetothehighnumberofemptycellsandalsoofidlevehicles
• Wehaveshownthatthedemandisgenerallyverypredictable,andthisalsocanbeexploitedforrelocation
• Wehavediscussedhowtosmartlydeploycleaningandmaintenancefacilities basedonvehicleflowsintheCSnetwork