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New Truck ModelsNew Truck Models

National Capital Region TPB

Travel Forecasting Subcommittee

William G. Allen, Jr., P.E.Transportation Planning Consultant

18 July 2008

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TimelineTimeline

• Feb. 04 – Apr. 07: COM model Feb. 04 – Apr. 07: COM model developeddeveloped

• 18 May 2007: COM presentation to TFS18 May 2007: COM presentation to TFS

• May 2007: truck models startedMay 2007: truck models started

• Jan. 2008: truck models completedJan. 2008: truck models completed

• Jan. – Jul. 08: TPB truck model testingJan. – Jul. 08: TPB truck model testing

• 23 May 2008: TPB truck presentation 23 May 2008: TPB truck presentation to TFSto TFS

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Vehicle TypesVehicle Types

• Commercial: Light-duty vehicle (car, Commercial: Light-duty vehicle (car, van, pickup) used for non-personal van, pickup) used for non-personal transportationtransportation

• Medium Truck: 2 axles, 6 tires Medium Truck: 2 axles, 6 tires (FHWA class 5)(FHWA class 5)

• Heavy Truck: 3+ axles (FHWA Heavy Truck: 3+ axles (FHWA classes 4 and 6-13)classes 4 and 6-13)– Includes BusesIncludes Buses

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DefinitionsDefinitions

• Heavy Truck: 3+ axles, Heavy Truck: 3+ axles, more than 6 tiresmore than 6 tires

• Medium Truck: 2 axle, Medium Truck: 2 axle, 6 tires6 tires

• Commercial: light duty Commercial: light duty vehicles used for vehicles used for businessbusiness

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Truck model historyTruck model history

• Original model developed from 1968 Original model developed from 1968 truck O-D surveytruck O-D survey

• Original truck types: light, medium, Original truck types: light, medium, heavyheavy

• Models updated in 1985, based on Models updated in 1985, based on limited count data and 1968 surveylimited count data and 1968 survey

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A new approachA new approach• Truck surveys don’t workTruck surveys don’t work

• Use new method developed for COM modelUse new method developed for COM model

• Trip-based method consistent with current Trip-based method consistent with current modelling proceduresmodelling procedures

• Borrow a starting modelBorrow a starting model

• Use counts to synthesize more countsUse counts to synthesize more counts

• Use counts to adjust starting tripsUse counts to adjust starting trips

• Use trip difference to refine the starting Use trip difference to refine the starting modelmodel

• Same method used for BMC, ARC, Ohio DOTSame method used for BMC, ARC, Ohio DOT

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Truck CountsTruck Counts

• Primary data source: MDOT countsPrimary data source: MDOT counts– 6 permanent counts6 permanent counts

– 315 short-term counts315 short-term counts

• Secondary data sources:Secondary data sources:– DC classification counts (11)DC classification counts (11)

– Virginia classification counts (33)Virginia classification counts (33)

– TPB 4-hour class. counts (148)TPB 4-hour class. counts (148)

– (2003) TPB External Truck Survey (10 (2003) TPB External Truck Survey (10 sites) sites)

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Daily truck count statisticsDaily truck count statistics

• Truck percentage: MTK=3.3%, Truck percentage: MTK=3.3%, HTK=3.2%HTK=3.2%

• TRK % range: 0.9% to 26.1% (US 1 TRK % range: 0.9% to 26.1% (US 1 in Jessup, MD)in Jessup, MD)

• TRK vol. range: 27 – 14,700 (I-95, TRK vol. range: 27 – 14,700 (I-95, Howard Co.)Howard Co.)

• Approx. TOD split: 19% AM, 14% Approx. TOD split: 19% AM, 14% PM, 67% OPPM, 67% OP

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Synthesized CountsSynthesized Counts• Model % HTK, % MTK by link using Model % HTK, % MTK by link using

count datacount data

• Logit function: % TRK = 1 / (1 + eLogit function: % TRK = 1 / (1 + eUU))

• U U lanes, facility type, area type, lanes, facility type, area type, jurisdictionjurisdiction

• Apply to all links with countsApply to all links with counts

• TRK “count” = est % TRK * countTRK “count” = est % TRK * count

• Thorough manual reviewThorough manual review

• Use actual counts where availableUse actual counts where available

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% TRK analysis findings% TRK analysis findings

• Synthesizing counts provides data Synthesizing counts provides data for DC and VAfor DC and VA

• % TRK goes up with:% TRK goes up with:– Less developed areasLess developed areas

– Higher facility typesHigher facility types

– Increasing lanes (MTK); decreasing Increasing lanes (MTK); decreasing lanes (HTK)lanes (HTK)

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Borrow a starting modelBorrow a starting model

• Simple linear regression model, from Simple linear regression model, from BMC modelBMC model

• Based on employment by type Based on employment by type (industrial, office, retail, other) and HHs(industrial, office, retail, other) and HHs

• Adjustments for area type, truck zoneAdjustments for area type, truck zone

• F’s from BMC and Quick Response F’s from BMC and Quick Response Freight ManualFreight Manual

• TOD percentages from MDOT count dataTOD percentages from MDOT count data

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Truck ZonesTruck Zones

• Zones with identifiable truck generatorsZones with identifiable truck generators

• Business districts, warehouses, Business districts, warehouses, manufacturing, transfer, airport, manufacturing, transfer, airport, deliverydelivery

• 1/0 flag1/0 flag

• 35 zones identified35 zones identified

• 3-5 times higher truck trip rate per job3-5 times higher truck trip rate per job

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Model StatisticsModel Statistics• Retail, Industrial empl are most importantRetail, Industrial empl are most important

• Higher trip rate (per empl) in less Higher trip rate (per empl) in less developed areasdeveloped areas

• External share External share distance from cordon distance from cordon

• 2005 trip totals: MTK=474 K, HTK=192 K, 2005 trip totals: MTK=474 K, HTK=192 K, total=666 Ktotal=666 K

• Avg. trip length: MTK=24 min., HTK=58 Avg. trip length: MTK=24 min., HTK=58 min., total=34 min.min., total=34 min.

• Prior model: 553K trips, 43 min. avgPrior model: 553K trips, 43 min. avg

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““Adaptable Assignment”Adaptable Assignment”

Assigntrips

Skim loads& counts

Adjusttrips

Finaltrip table

Deltatrip table

Repeat

(7 iter.)

Startingtrip table

Startingmodel

Inform

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Delta analysisDelta analysis

• Subtract starting trips from new tripsSubtract starting trips from new trips

• Analyze trip end summary of Analyze trip end summary of differencedifference

• Correlate with HH, employmentCorrelate with HH, employment

• Use to inform model (revise coeffs.)Use to inform model (revise coeffs.)

• Keep “delta” table as adjustmentKeep “delta” table as adjustment

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Calibration adjustmentCalibration adjustment

• O/D table of mostly small adjustmentsO/D table of mostly small adjustments

• Accounts for random error in Accounts for random error in assignmentassignment

• Table totals: MTK=7.8 K, HTK=25.7 KTable totals: MTK=7.8 K, HTK=25.7 K

• Tend to be short trips; no other patternTend to be short trips; no other pattern

• Carried along for forecasting, added to Carried along for forecasting, added to model’s starting trip tablemodel’s starting trip table

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Validation results (2005)Validation results (2005)

• Prior model (v2.1D, fall 2005)Prior model (v2.1D, fall 2005)– % RMSE: 104%, volume/count: 1.16% RMSE: 104%, volume/count: 1.16

– 553 K trips 553 K trips

• Starting modelStarting model– % RMSE: 111%, volume/count: 1.33% RMSE: 111%, volume/count: 1.33

– 632 K trips632 K trips

• Final modelFinal model– % RMSE: 51%, volume/count: 1.07% RMSE: 51%, volume/count: 1.07

– 666 K trips666 K trips

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More resultsMore results

• 2005 VMT2005 VMT– Current: 11.4 MCurrent: 11.4 M

– New: 10.8 M (-5%)New: 10.8 M (-5%)

– Trips go up, average length goes downTrips go up, average length goes down

• 2030 estimate2030 estimate- Trips: 916 K (+38%)Trips: 916 K (+38%)

- VMT: 17.3 M (+60%)VMT: 17.3 M (+60%)

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ConclusionsConclusions• TPB wanted a cost-effective, practical, proven TPB wanted a cost-effective, practical, proven

approachapproach

• Goods movement approach not readyGoods movement approach not ready

• Truck trips are complex -- not suited to an Truck trips are complex -- not suited to an aggregate four-step approachaggregate four-step approach

• Truck travel is related to national policy and Truck travel is related to national policy and macroeconomic factors beyond our macroeconomic factors beyond our knowledgeknowledge

• Don’t wait 20 years to revisit the truck modelsDon’t wait 20 years to revisit the truck models