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New Truck Models

New Truck Models. National Capital Region TPB Travel Forecasting Subcommittee William G. Allen, Jr., P.E. Transportation Planning Consultant 18 July 2008. Timeline. Feb. 04 – Apr. 07: COM model developed 18 May 2007: COM presentation to TFS May 2007: truck models started

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New Truck Models

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  1. New Truck Models National Capital Region TPB Travel Forecasting Subcommittee William G. Allen, Jr., P.E. Transportation Planning Consultant 18 July 2008

  2. Timeline • Feb. 04 – Apr. 07: COM model developed • 18 May 2007: COM presentation to TFS • May 2007: truck models started • Jan. 2008: truck models completed • Jan. – Jul. 08: TPB truck model testing • 23 May 2008: TPB truck presentation to TFS

  3. Vehicle Types • Commercial: Light-duty vehicle (car, van, pickup) used for non-personal transportation • Medium Truck: 2 axles, 6 tires (FHWA class 5) • Heavy Truck: 3+ axles (FHWA classes 4 and 6-13) • Includes Buses

  4. Definitions • Heavy Truck: 3+ axles, more than 6 tires • Medium Truck: 2 axle, 6 tires • Commercial: light duty vehicles used for business

  5. Truck model history • Original model developed from 1968 truck O-D survey • Original truck types: light, medium, heavy • Models updated in 1985, based on limited count data and 1968 survey

  6. A new approach • Truck surveys don’t work • Use new method developed for COM model • Trip-based method consistent with current modelling procedures • Borrow a starting model • Use counts to synthesize more counts • Use counts to adjust starting trips • Use trip difference to refine the starting model • Same method used for BMC, ARC, Ohio DOT

  7. Truck Counts • Primary data source: MDOT counts • 6 permanent counts • 315 short-term counts • Secondary data sources: • DC classification counts (11) • Virginia classification counts (33) • TPB 4-hour class. counts (148) • (2003) TPB External Truck Survey (10 sites)

  8. Daily truck count statistics • Truck percentage: MTK=3.3%, HTK=3.2% • TRK % range: 0.9% to 26.1% (US 1 in Jessup, MD) • TRK vol. range: 27 – 14,700 (I-95, Howard Co.) • Approx. TOD split: 19% AM, 14% PM, 67% OP

  9. Synthesized Counts • Model % HTK, % MTK by link using count data • Logit function: % TRK = 1 / (1 + eU) • U  lanes, facility type, area type, jurisdiction • Apply to all links with counts • TRK “count” = est % TRK * count • Thorough manual review • Use actual counts where available

  10. % TRK analysis findings • Synthesizing counts provides data for DC and VA • % TRK goes up with: • Less developed areas • Higher facility types • Increasing lanes (MTK); decreasing lanes (HTK)

  11. Borrow a starting model • Simple linear regression model, from BMC model • Based on employment by type (industrial, office, retail, other) and HHs • Adjustments for area type, truck zone • F’s from BMC and Quick Response Freight Manual • TOD percentages from MDOT count data

  12. Truck Zones • Zones with identifiable truck generators • Business districts, warehouses, manufacturing, transfer, airport, delivery • 1/0 flag • 35 zones identified • 3-5 times higher truck trip rate per job

  13. Model Statistics • Retail, Industrial empl are most important • Higher trip rate (per empl) in less developed areas • External share  distance from cordon • 2005 trip totals: MTK=474 K, HTK=192 K, total=666 K • Avg. trip length: MTK=24 min., HTK=58 min., total=34 min. • Prior model: 553K trips, 43 min. avg

  14. “Adaptable Assignment” Starting model Starting trip table Assign trips Repeat (7 iter.) Skim loads & counts Final trip table Adjust trips Delta trip table Inform

  15. Delta analysis • Subtract starting trips from new trips • Analyze trip end summary of difference • Correlate with HH, employment • Use to inform model (revise coeffs.) • Keep “delta” table as adjustment

  16. Calibration adjustment • O/D table of mostly small adjustments • Accounts for random error in assignment • Table totals: MTK=7.8 K, HTK=25.7 K • Tend to be short trips; no other pattern • Carried along for forecasting, added to model’s starting trip table

  17. Validation results (2005) • Prior model (v2.1D, fall 2005) • % RMSE: 104%, volume/count: 1.16 • 553 K trips • Starting model • % RMSE: 111%, volume/count: 1.33 • 632 K trips • Final model • % RMSE: 51%, volume/count: 1.07 • 666 K trips

  18. More results • 2005 VMT • Current: 11.4 M • New: 10.8 M (-5%) • Trips go up, average length goes down • 2030 estimate • Trips: 916 K (+38%) • VMT: 17.3 M (+60%)

  19. Conclusions • TPB wanted a cost-effective, practical, proven approach • Goods movement approach not ready • Truck trips are complex -- not suited to an aggregate four-step approach • Truck travel is related to national policy and macroeconomic factors beyond our knowledge • Don’t wait 20 years to revisit the truck models

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