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Ohio Traffic Forecasting Manual

Ohio Traffic Forecasting Manual. Module 3: Travel Demand Modeling. Training Organization. Module 2: Traffic Forecasting Methodologies Data and Parameters, Step-by-Step Procedures, Examples. Ohio Traffic Forecasting Training Modules. Module 1: Traffic Forecasting Background

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Ohio Traffic Forecasting Manual

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  1. Ohio Traffic Forecasting Manual Module 3: Travel Demand Modeling

  2. Training Organization Module 2: Traffic Forecasting Methodologies Data and Parameters, Step-by-Step Procedures, Examples Ohio Traffic Forecasting Training Modules Module 1: Traffic Forecasting Background Policy, Administrative and Technical Overview Module 3: Travel Demand Forecast Modeling Model Selection, Checks and Refinements Intended Audience Forecast User Traffic Forecaster/Modeler Ohio Traffic Forecasting Manual

  3. Outline – Part II • Standard Model Checking • Advanced Model Checking • Special Requirements Ohio Traffic Forecasting Manual

  4. Documentation and Coordination • Throughout this training, the following symbols indicate: • Items that are required or suggested for documentation • Items that are required or suggested for coordination with ODOT M&F Ohio Traffic Forecasting Manual

  5. Standard Model Checking

  6. Using the Model for Projects • The Model of Record will generally need revision to provide the location-specific accuracy needed for project level forecasts. • This is accomplished with 3 processes: • Model Checking • Model Refinement • Model Adjustment • NOTE: The checks/refinements/adjustments covered in this training focus on the needs of highway projects, transit and policy type projects will have their own requirements outside the scope of this training. Ohio Traffic Forecasting Manual

  7. Model Checking • All model work should begin with the validated Model of Record. • Model checking is generally conducted at two levels: • For the entire regional model • Within the project study area Project Location Study Area Ohio Traffic Forecasting Manual

  8. Regional Checking • Regional (system-wide) checks should be performed when: • The base year is different from the validation year. • Model adjustments are made specifically for a project. • The checks conducted at the regional level are simply a subset of the more extensive series of checks that will be conducted within the study area. The regional checks to be discussed include: • %RMSE Check • VMT Check • Screen line Check • V/G Ratio Check Ohio Traffic Forecasting Manual

  9. Study Area Checks • Study area checks should be conducted for all projects. The first four checks are the same as conducted regionally: • %RMSE (or Percent Difference) • VMT • Screen line • V/G Ratio • Additional study area checks include: • Network Coding • Base Land Use • Forecast Land Use • Growth Rates Ohio Traffic Forecasting Manual

  10. Isolating Study Area Statistics • With the standard MPO model, these can be checked on the study area by coding a unique project identifier in field PROJID on the network. Ohio Traffic Forecasting Manual

  11. Isolating Study Area Statistics • All assignment validation statistics are reported for both the region and all unique PROJID. Ohio Traffic Forecasting Manual

  12. Isolating Study Area Statistics • If you don’t have this capability inherent, you can add a link attribute (link-attribute-add) to accomplish the same thing (you’d need to add conditional logic to your reporting scripts as well). Ohio Traffic Forecasting Manual

  13. %RMSE Check • The root mean square error (RMSE) is a measure of the relative error of the assignment compared to actual traffic counts. When compared to the ground count, it is used to measure the relative accuracy of the assignment. Ohio Traffic Forecasting Manual

  14. %RMSE Check • %RMSE is applied to volume groups rather than links. • Ignored for directional volumes < 500/day. • Allowable %RMSE by Directional Link Volume Group %RMSE reported graphically or in tabular format showing achieved versus desired level by volume group. Ohio Traffic Forecasting Manual

  15. %RMSE Check • %RMSE is contained in report 7 of the standard model: • RPT7MPOYRVALAA.DBF • This can be imported to spreadsheet and plotted versus the desired %RMSE curve. • Conversely, percent difference can be calculated directly on the links (possibly by saving the study links to DBF and importing to spreadsheet). Ohio Traffic Forecasting Manual

  16. %RMSE Check Ohio Traffic Forecasting Manual

  17. VMT Check • The Vehicle Miles Traveled (VMT) check calculates the volume times the distance of the link to produce vehicle miles. • VMT checking is somewhat less important at the study area level, particularly when there are few links in a category (in which case individual percent differences are more important). • Still, it provides a benchmark on model performance, particularly for larger study areas. • VMT Check Acceptance Criteria Ohio Traffic Forecasting Manual

  18. VMT Check • VMT summary is contained in report 8 of the standard model: • RPT8MPOYRVALVMTAA.DBF Ohio Traffic Forecasting Manual

  19. Screen Line Check • A true screen line crosses the entire model area. • A cut line (or auxiliary screen line) is a line which intersects several parallel roadways which form a corridor. • A cordon line is a special case of the screen line which connects back upon itself, isolating all traffic movements into and out of an area. Ohio Traffic Forecasting Manual

  20. Screen Line Check • Screen lines, cut lines and cordon lines are collectively referred to as screen lines. • A screen line check consists of adding the total volume on a screen line and comparing to that of the corresponding ground counts. • The add a lane, drop a line criterion is used on the % difference. • Higher volume corridors are allowed less error. • Lower volume corridors are allowed more error. • Total number of lanes in the corridor should be correct. Ohio Traffic Forecasting Manual

  21. Screen Line Check • Screen line checking is less important at the study area level. • However, for some large study areas, some formalized screen lines might be defined for the study area to ensure certain important corridor flows are considered. • The screen line summary is contained in report 9 of the standard model: • RPT9MPOYRSCRNLNAA.DBF Ohio Traffic Forecasting Manual

  22. V/G Ratio Check • The V/G ratio check is an alternative way to express percent differences in map format: Volume / ground count • Shown as a link map colored as follows: Include link map, annotated with the directional assigned volume and count Ohio Traffic Forecasting Manual

  23. Other Checks • If model adjustments or recalibration are performed, additional checks should be conducted identical to the relevant checks report in the model’s validation report. Ohio Traffic Forecasting Manual

  24. Network Coding Check • Network checking is a comparison of the coded attributes with known conditions. • Networks should be thoroughly checked in the study area. • Independent sources such as ODOT Roadway Information Database, aerial photos and windshield surveys should be conducted to ensure the network data is correct in the study area. • Additional roadways might also be brought into the network during the refinement stage to provide greater network detail (all roadways imposing traffic control on modeled roads of interest should be included). Ohio Traffic Forecasting Manual

  25. Network Coding Check • Besides ensuring the proper roadways are coded and contain the correct directionality, the following attributes should be checked: Ohio Traffic Forecasting Manual

  26. Network Coding Check • These attributes are all contained at the front of the link attributes list for the standard models. • If time of day specific overrides exist, they are further down the attribute list and must be checked as well. • Note that TURNLANE and IXTYPE are intersection attributes coded on links, it is important to be careful to keep these associated with the correct intersection node. Ohio Traffic Forecasting Manual

  27. Base Year Land Use Check • Base year land use should be checked in the study area in three ways (the level of checking depending on the magnitude of the project): • Check consistency in a spreadsheet • Check accuracy versus independent data in GIS • Check trip generation versus ITE Trip Generation Ohio Traffic Forecasting Manual

  28. Land Use Consistency Check • Import the base year SE file (for the standard model this will be called MPOYRZDAA.DBF) • Calculate ratios between various variables such as: • HHPOP/HH • WRKER/HH • VEH/HH • POP18/POP • HOTELROOM/NAICS72 • ENROLL/NAICS61 • Graphs can also be useful here. Ohio Traffic Forecasting Manual

  29. Land Use Accuracy Check • Compare the variables to other sources such as: • Census • QCEW/InfoUSA • Previous Traffic Impact Studies • Windshield surveys/aerial photos • GIS is a useful tool to bring these data together for this analysis. Ohio Traffic Forecasting Manual

  30. Land Use Accuracy Check • Centroid connectors should be checked versus actual access points. Actual Old New Ohio Traffic Forecasting Manual

  31. Forecast Year Land Use Check • Consistency checks similar to those for the base year should be conducted in a spreadsheet. • In addition, the forecast socio-economic data should be compared to the base year to ascertain whether the implied growth makes sense. Sometimes, forecast year variables are updated with methodologies that are different from those used to develop base year variable, resulting in major inconsistencies. Ohio Traffic Forecasting Manual

  32. Growth Rate Check • At the most important project locations, the annual traffic growth rate implied by the model should be compared to independent sources such as: • Past traffic count trends • HPMS VMT growth rates • ODOT Congestion Management Process growth rates (TIMS) • ODOT annual adjustment factors report • Population/employment growth trends (ODOD projects etc.) http://www.dot.state.oh.us/Divisions/Planning/TechServ/traffic/Pages/default.aspx http://www.odod.state.oh.us/research/ Ohio Traffic Forecasting Manual

  33. Percent Difference Check • The Percent Difference check is the same as the %RMSE check conducted for the entire model. • The percent deviation of the daily directional volume of individual links in the study area is compared to the Maximum Desirable Deviation Curve. (by direction!) Ohio Traffic Forecasting Manual

  34. Percent Difference Check Ohio Traffic Forecasting Manual

  35. Advanced Model Checking

  36. Advanced Model Checking • There are additional study area checks that should be conducted for larger, more complex projects. • These include: • Travel Time • Paths • Select Links • Distribution • Modal • Generation • If “Refined Alternative Level Traffic” will be produced for operational level analysis, these checks are required! Ohio Traffic Forecasting Manual

  37. Travel Time Checks • When independent travel time estimates are available (such as those now made available by ODOT and FHWA), the network travel times/speeds obtained from the paths or on individual links can be checked. • SPDMOD field can then be used to adjust these if necessary. Ohio Traffic Forecasting Manual

  38. Path Checks • Paths taken through the network can be checked to insure they are logical. They are best checked by using the path file output from a Cube assignment. • Two possible examples: • Making sure a freeway-freeway movement stays on the freeway through the study area. • Making sure most through traffic follows a signed state route. Ohio Traffic Forecasting Manual

  39. Select Link Analysis • Select link analysis shows where the traffic using a given link comes from/goes to and all other links used. • It is useful for diagnosing problems with specific links (similar to path checking and select zone maps shown previously) also critical for weave analysis. Ohio Traffic Forecasting Manual

  40. Select Link Analysis • When the path file isn’t too big, it is easiest to do the select link analysis on the fly using this file. Otherwise, the assignment script must be modified to do this. Ohio Traffic Forecasting Manual

  41. Select Link Analysis • To save the select link directly when performing an assignment, the script is modified as follows: • This will save the select link assignment of cars and trucks in output volume fields 3 and 4 (1 and 2 contain the total cars and trucks). • It is important to have a “V=“ statement in the ADJUST phase when doing this (standard model does). Ohio Traffic Forecasting Manual

  42. Distribution Checks • Screen line checks, as well as the desire line and select zone checks shown under trip rate checking, provide checks on the trip distribution of the model (how far and where trips from a given zone choose to go). • However, sometimes more detailed checking of the trip table (generally at a district level) is needed using independent data such as: • CTPP journey to work data • Trip table developed from surveys or purchased from vendors who process anonymous signal data (cell phones etc.) into OD tables Ohio Traffic Forecasting Manual

  43. Distribution Checks • When model ADJUSTMENTS (as detailed later) occur, it is usually necessary to recheck the region-wide distribution statistics just as is done during the base year validation: • Check average trip lengths by purpose • Percent of intrazonal trips by purpose • Trip length frequency distribution coincidence ratio by purpose Ohio Traffic Forecasting Manual

  44. Distribution Checks • File MPOYRTLFDAA.PRN from the standard model contains output TLFD’s that can be imported to a spreadsheet for analysis. • Report RPT4_DIST_TOD.PRN from the standard model contains the trip distribution summary report with average trip lengths and percent intrazonal statistics. Ohio Traffic Forecasting Manual

  45. Modal Checks • This training is focused on highway projects due to the many special circumstances involved with transit, however a few brief points: • The study area for transit studies will likely be defined by transit routes. • Route ridership is the primary thing to check and is generally available from the operator. • Other statistics ,such as transfer rates and user profiles, are often available for the entire system. • Special transit on-board surveys can provide other data, like stop specific boarding/alighting and route-specific OD patterns. • CTPP Journey to Work has modal OD patterns Ohio Traffic Forecasting Manual

  46. Generation Checks • Generation checks are especially useful to check trip rates when special generators are added, regional generation rates are changed, or TIS trips are being overlaid. Ohio Traffic Forecasting Manual

  47. Trip Rate Checks • Trips coming out of zones in the study area can be compared to ITE Trip Generation rates for non-residential land uses. • Additionally, previous Traffic Impact Studies should be consulted to ensure consistency with past assumptions. • Major discrepancies can be accommodated with special generators. Ohio Traffic Forecasting Manual

  48. Trip Rate Checks • There are various graphical ways to check trips from a zone in Cube or GIS. • Desire Line Map • Select Zone Map - Similar to select link, but selects a zone and shows the roadways that are carrying traffic to/from that zone. Ohio Traffic Forecasting Manual

  49. Trip Rate Checks • In Cube, open the trip table and the network. • With the network active, select Analysis > Link to Matrix. Scaled Symbol Theme/Chart Map Color Zone Map Ohio Traffic Forecasting Manual

  50. Special Requirements

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