7.1 Version NERPMAB1v2

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This section documents the improvements that were made to the NERPM-AB model since the adoption of the model as part as the “Path Forward 2040” Long Range Transportation Plan. The improvements focused on improving its usability related to runtime, user’s catalog interface, and model usability


The investigation of alternative methods to reduce system run times focused on the highway network assignments and global feedback iterations. After investigating several different options for reducing runtime the following improvements were made:

Feedback Loops

The transition of model outputs from one feedback loop to the next one and feedback loop termination criteria were adjusted in the new model. The model has been set up such that the weighted-average volume for each link is calculated at the end of each loop, based on the current and previous feedback loop flows. These averaged volumes are used to generate skims for the next iteration of the model system and are fed back to the demand models (DaySim).

In addition, rather than terminate based on a fixed number of iterations, the model has been set up to terminate the feedback loops if both of the following criteria are met:

  1. Change in total AM and PM VMT of two successive feedback loops is less than five percent
  2. The AM and PM volumes of more than 95 percent of freeway and arterial links change less than five percent in two successive loops.

The net effect of these changes are that the model runs one feedback loop less than the original model for the 2010 baseline scenario.

Highway Traffic Assignment

The model is able to run midday and nighttime highway assignments in parallel. The user can assign computer logical processors to time periods by filling the corresponding keys added to the user interface. Figure 7-1, below, shows an example of the Cube catalog (last page of user interface page) for a computer with 8 logical processors. The AM and the PM assignments use all available logical processors, whereas the midday and nighttime assignments use different logical processors and can therefore run in parallel.

The model currently runs AM and PM assignments in sequence; however, it will be able to run them in parallel with minor changes in the model. In this case, the model should know which computer logical processor is the first one used for AM assignment (also which one is the first one for PM period). The interface has these two keys now and, since they are not run in parallel, the value for them should be higher than number of computer logical processors. The default value, therefore, was set to 25, which is suitable for any machine with up to 24 logical processors.

Figure 7-1: Assigning computer logical processors to highway assignments by time period

Figure 7-1.png

Highway Traffic Assignment Parameters

The assignment convergence criterion was changed to the accepted standard practice of relative gap. In addition, the maximum number of iterations was increased from 50 to 150, allowing for greater accuracy in the assignment process. The model is setup to use a tighter relative gap in the highway assignment after the first loop. Following best practice recommendations for regional highway assignments, it is recommended that this relative gap be set to 0.0001. The user may increase or decrease the relative gap, depending on the accuracy level required for the analysis under consideration. Figure 7-2 shows that the relative gap used after the first feedback loop was added to the interface as a key controlled by the user.

Figure 7-2: Setting the relative gap used in highway assignment after the second feedback loop

Figure 7-2.png

Post-Process Analysis

The Select link analysis is set to run after the feedback loop. The user selects the option to run a selected link analysis on typically the third page of the user interface, as shown in Figure 7-3. The select link analysis can be run for any of the time periods, including the daily assignment, by selecting the specific option. In order to run the daily select link option, all the time periods need to be run for the select link.

If the user wants to save the congested path files, they can choose the option to save the path file for a particular period. The paths are saved in an extra highway assignment run at the end of the model based on the final congested network. It should be noted that Cube Cluster does not support the use of multiple logical processors for path saving; therefore, this step takes a bit longer than would a normal assignment that can be distributed across processors.

Figure 7-3: Keys used to define links for select link analysis and time periods for path saving

Figure 7-3a.png

Figure 7-3b.png

Table 7-1 lists all the fields in the loaded network files. The two columns on the right lists the fields associated with the links which the user selected in the "select link" option shown in Figure 7-3. The yellow rows on the table are used in the calculation listed on the last row of the table and calculates the total link volume.

Table 7-1 NERPAB1v2 Loaded highway network fields

New Variable Description New Variable Description


Directional 2010 AADT count value, 0 if not available

AMCOUNT Directional 2010 AM count value, 0 if not


MDCOUNT Directional 2010 MD count value, 0 if not


PMCOUNT Directional 2010 PM count value, 0 if not


NTCOUNT Directional 2010 NT count value, 0 if not


SCREENLINE_YR10 Screenline number for year 2010
NT_VL_TOT_10A Night offpeak time total volume for year 2010 and

scenario "A"

NTSL_VL_TOT_10A Selected Link Night offpeak time total volume for year

2010 and scenario "A"

NT_VL_DA_10A Night offpeak DA-Free&Toll-II&IE+EE


NTSL_VL_DA_10A Selected Link Night offpeak

DA-Free&Toll-II&IE+EE traffic

NT_F_DA_10A Night offpeak DA-II&IE-Free traffic NTSL_F_DA_10A Selected Link Night offpeak DA-II&IE-Free


NT_T_DA_10A Night offpeak DA-II&IE-Toll NTSL_T_DA_10A Selected Link Night offpeak DA-II&IE-Toll
NT_F_EDA_10A Night offpeak DA-EE-Free NTSL_F_EDA_10A Selected Link Night offpeak DA-EE-Free
NT_T_EDA_10A Night offpeak DA-EE-Toll NTSL_T_EDA_10A Selected Link Night offpeak DA-EE-Toll
NT_VL_SR2_10A Night offpeak SR2-Free&Toll-II&IE+EE


NTSL_VL_SR2_10A Selected Link Night offpeak

SR2-Free&Toll-II&IE+EE traffic

NT_F_SR2_10A Night offpeak SR2-II&IE-Free NTSL_F_SR2_10A Selected Link Night offpeak SR2-II&IE-Free
NT_T_SR2_10A Night offpeak SR2-II&IE-Toll NTSL_T_SR2_10A Selected Link Night offpeak SR2-II&IE-Toll
NT_F_ESR2_10A Night offpeak SR2-EE-Free NTSL_F_ESR2_10A Selected Link Night offpeak SR2-EE-Free
NT_T_ESR2_10A Night offpeak SR2-EE-Toll NTSL_T_ESR2_10A Selected Link Night offpeak SR2-EE-Toll
NT_VL_SR3_10A Night offpeak SR3-Free&Toll-II&IE+EE


NTSL_VL_SR3_10A Selected Link Night offpeak

SR3-Free&Toll-II&IE+EE traffic

NT_F_SR3_10A Night offpeak SR3-II&IE-Free NTSL_F_SR3_10A Selected Link Night offpeak SR3-II&IE-Free
NT_T_SR3_10A Night offpeak SR3-II&IE-Toll NTSL_T_SR3_10A Selected Link Night offpeak SR3-II&IE-Toll
NT_F_ESR3_10A Night offpeak SR3-EE-Free NTSL_F_ESR3_10A Selected Link Night offpeak SR3-EE-Free
NT_T_ESR3_10A Night offpeak SR3-EE-Toll NTSL_T_ESR3_10A Selected Link Night offpeak SR3-EE-Toll
NT_VL_TRK_10A Night offpeak Truck-II&IE+EE+Port NTSL_VL_TRK_10A Selected Link Night offpeak


NT_VL_PRTTK_10A Night offpeak Port-Truck NTSL_VL_PRTTK_10A Selected Link Night offpeak Port-Truck
NT_VL_EXT_10A Night offpeak EXT-TRK +


NTSL_VL_EXT_10A Selected Link Night offpeak EXT-TRK +


NT_VC_10A Night offpeak V/C Ratio
NT_CGSPEED_10A Night offpeak average congested speed
NT_VMT_10A Night offpeak VMT
NT_VHT_10A Night offpeak VHT
NT_CGTIME_10A Night offpeak congested travel time
NT_FLGCGSPDZERO Night offpeak congested speed is 0 indicator, 1 if

speed is 0

NT_VCCAPRTO_10A Night offpeak V/C Ratio (same as VC_10A)
PM_VL_TOT_10A PM peak time total volume for year 2010 and scenario


PMSL_VL_TOT_10A Selected Link PM peak time total volume for year 2010

and scenario "A"

PM_VL_DA_10A PM peak DA-Free&Toll-II&IE+EE traffic PMSL_VL_DA_10A Selected Link PM peak DA-Free&Toll-II&IE+EE


PM_F_DA_10A PM peak DA-II&IE-Free traffic PMSL_F_DA_10A Selected Link PM peak DA-II&IE-Free traffic
PM_T_DA_10A PM peak DA-II&IE-Toll PMSL_T_DA_10A Selected Link PM peak DA-II&IE-Toll
PM_F_EDA_10A PM peak DA-EE-Free PMSL_F_EDA_10A Selected Link PM peak DA-EE-Free
PM_T_EDA_10A PM peak DA-EE-Toll PMSL_T_EDA_10A Selected Link PM peak DA-EE-Toll
PM_VL_SR2_10A PM peak SR2-Free&Toll-II&IE+EE traffic PMSL_VL_SR2_10A Selected Link PM peak SR2-Free&Toll-II&IE+EE


PM_F_SR2_10A PM peak SR2-II&IE-Free PMSL_F_SR2_10A Selected Link PM peak SR2-II&IE-Free
PM_T_SR2_10A PM peak SR2-II&IE-Toll PMSL_T_SR2_10A Selected Link PM peak SR2-II&IE-Toll
PM_F_ESR2_10A PM peak SR2-EE-Free PMSL_F_ESR2_10A Selected Link PM peak SR2-EE-Free
PM_T_ESR2_10A PM peak SR2-EE-Toll PMSL_T_ESR2_10A Selected Link PM peak SR2-EE-Toll
PM_VL_SR3_10A PM peak SR3-Free&Toll-II&IE+EE traffic PMSL_VL_SR3_10A Selected Link PM peak SR3-Free&Toll-II&IE+EE


PM_F_SR3_10A PM peak SR3-II&IE-Free PMSL_F_SR3_10A Selected Link PM peak SR3-II&IE-Free
PM_T_SR3_10A PM peak SR3-II&IE-Toll PMSL_T_SR3_10A Selected Link PM peak SR3-II&IE-Toll
PM_F_ESR3_10A PM peak SR3-EE-Free PMSL_F_ESR3_10A Selected Link PM peak SR3-EE-Free
PM_T_ESR3_10A PM peak SR3-EE-Toll PMSL_T_ESR3_10A Selected Link PM peak SR3-EE-Toll
PM_VL_TRK_10A PM peak Truck-II&IE+EE+Port PMSL_VL_TRK_10A Selected Link PM peak Truck-II&IE+EE+Port
PM_VL_PRTTK_10A PM peak Port-Truck PMSL_VL_PRTTK_10A Selected Link PM peak Port-Truck
PM_VL_EXT_10A PM peak EXT-TRK + EE-Free&Toll(DA+SR2+SR3) PMSL_VL_EXT_10A Selected Link PM peak EXT-TRK +


PM_VC_10A PM peak V/C Ratio
PM_CGSPEED_10A PM peak average congested speed
PM_VMT_10A PM peak VMT
PM_VHT_10A PM peak VHT
PM_CGTIME_10A PM peak congested travel time
PM_FLGCGSPDZERO PM peak congested speed is 0 indicator, 1 if speed is


PM_VCCAPRTO_10A PM peak V/C Ratio (same as VC_10A)
MD_VL_TOT_10A MD offpeak time total volume for year 2010 and

scenario "A"

MDSL_VL_TOT_10A Selected Link MD offpeak time total volume for year

2010 and scenario "A"

MD_VL_DA_10A MD offpeak DA-Free&Toll-II&IE+EE traffic MDSL_VL_DA_10A Selected Link MD offpeak DA-Free&Toll-II&IE+EE


MD_F_DA_10A MD offpeak DA-II&IE-Free traffic MDSL_F_DA_10A Selected Link MD offpeak DA-II&IE-Free


MD_T_DA_10A MD offpeak DA-II&IE-Toll MDSL_T_DA_10A Selected Link MD offpeak DA-II&IE-Toll
MD_F_EDA_10A MD offpeak DA-EE-Free MDSL_F_EDA_10A Selected Link MD offpeak DA-EE-Free
MD_T_EDA_10A MD offpeak DA-EE-Toll MDSL_T_EDA_10A Selected Link MD offpeak DA-EE-Toll
MD_VL_SR2_10A MD offpeak SR2-Free&Toll-II&IE+EE traffic MDSL_VL_SR2_10A Selected Link MD offpeak

SR2-Free&Toll-II&IE+EE traffic

MD_F_SR2_10A MD offpeak SR2-II&IE-Free MDSL_F_SR2_10A Selected Link MD offpeak SR2-II&IE-Free
MD_T_SR2_10A MD offpeak SR2-II&IE-Toll MDSL_T_SR2_10A Selected Link MD offpeak SR2-II&IE-Toll
MD_F_ESR2_10A MD offpeak SR2-EE-Free MDSL_F_ESR2_10A Selected Link MD offpeak SR2-EE-Free
MD_T_ESR2_10A MD offpeak SR2-EE-Toll MDSL_T_ESR2_10A Selected Link MD offpeak SR2-EE-Toll
MD_VL_SR3_10A MD offpeak SR3-Free&Toll-II&IE+EE traffic MDSL_VL_SR3_10A Selected Link MD offpeak

SR3-Free&Toll-II&IE+EE traffic

MD_F_SR3_10A MD offpeak SR3-II&IE-Free MDSL_F_SR3_10A Selected Link MD offpeak SR3-II&IE-Free
MD_T_SR3_10A MD offpeak SR3-II&IE-Toll MDSL_T_SR3_10A Selected Link MD offpeak SR3-II&IE-Toll
MD_F_ESR3_10A MD offpeak SR3-EE-Free MDSL_F_ESR3_10A Selected Link MD offpeak SR3-EE-Free
MD_T_ESR3_10A MD offpeak SR3-EE-Toll MDSL_T_ESR3_10A Selected Link MD offpeak SR3-EE-Toll
MD_VL_TRK_10A MD offpeak Truck-II&IE+EE+Port MDSL_VL_TRK_10A Selected Link MD offpeak Truck-II&IE+EE+Port
MD_VL_PRTTK_10A MD offpeak Port-Truck MDSL_VL_PRTTK_10A Selected Link MD offpeak Port-Truck
MD_VL_EXT_10A MD offpeak EXT-TRK + EE-Free&Toll(DA+SR2+SR3) MDSL_VL_EXT_10A Selected Link MD offpeak EXT-TRK +


MD_VC_10A MD offpeak V/C Ratio
MD_CGSPEED_10A MD offpeak average congested speed
MD_VMT_10A MD offpeak VMT
MD_VHT_10A MD offpeak VHT
MD_CGTIME_10A MD offpeak congested travel time
MD_FLGCGSPDZERO MD offpeak congested speed is 0 indicator, 1 if speed

is 0

MD_VCCAPRTO_10A MD offpeak V/C Ratio (same as VC_10A)



peak time total volume for year 2010 and scenario "A"

AMSL_VL_TOT_10A Selected Link AM peak time total volume for year 2010

and scenario "A"

AM_VL_DA_10A AM peak DA-Free&Toll-II&IE+EE traffic AMSL_VL_DA_10A Selected Link AM peak DA-Free&Toll-II&IE+EE


AM_F_DA_10A AM peak DA-II&IE-Free traffic AMSL_F_DA_10A Selected Link AM peak DA-II&IE-Free traffic
AM_T_DA_10A AM peak DA-II&IE-Toll AMSL_T_DA_10A Selected Link AM peak DA-II&IE-Toll
AM_F_EDA_10A AM peak DA-EE-Free AMSL_F_EDA_10A Selected Link AM peak DA-EE-Free
AM_T_EDA_10A AM peak DA-EE-Toll AMSL_T_EDA_10A Selected Link AM peak DA-EE-Toll
AM_VL_SR2_10A AM peak SR2-Free&Toll-II&IE+EE traffic AMSL_VL_SR2_10A Selected Link AM peak SR2-Free&Toll-II&IE+EE


AM_F_SR2_10A AM peak SR2-II&IE-Free AMSL_F_SR2_10A Selected Link AM peak SR2-II&IE-Free
AM_T_SR2_10A AM peak SR2-II&IE-Toll AMSL_T_SR2_10A Selected Link AM peak SR2-II&IE-Toll
AM_F_ESR2_10A AM peak SR2-EE-Free AMSL_F_ESR2_10A Selected Link AM peak SR2-EE-Free
AM_T_ESR2_10A AM peak SR2-EE-Toll AMSL_T_ESR2_10A Selected Link AM peak SR2-EE-Toll
AM_VL_SR3_10A AM peak SR3-Free&Toll-II&IE+EE traffic AMSL_VL_SR3_10A Selected Link AM peak SR3-Free&Toll-II&IE+EE


AM_F_SR3_10A AM peak SR3-II&IE-Free AMSL_F_SR3_10A Selected Link AM peak SR3-II&IE-Free
AM_T_SR3_10A AM peak SR3-II&IE-Toll AMSL_T_SR3_10A Selected Link AM peak SR3-II&IE-Toll
AM_F_ESR3_10A AM peak SR3-EE-Free AMSL_F_ESR3_10A Selected Link AM peak SR3-EE-Free
AM_T_ESR3_10A AM peak SR3-EE-Toll AMSL_T_ESR3_10A Selected Link AM peak SR3-EE-Toll
AM_VL_TRK_10A AM peak Truck-II&IE+EE+Port AMSL_VL_TRK_10A Selected Link AM peak Truck-II&IE+EE+Port
AM_VL_PRTTK_10A AM peak Port-Truck AMSL_VL_PRTTK_10A Selected Link AM peak Port-Truck
AM_VL_EXT_10A AM peak EXT-TRK + EE-Free&Toll(DA+SR2+SR3) AMSL_VL_EXT_10A Selected Link AM peak EXT-TRK +


AM_VC_10A AM peak V/C Ratio
AM_CGSPEED_10A AM peak average congested speed
AM_VMT_10A AM peak VMT
AM_VHT_10A AM peak VHT
AM_CGTIME_10A AM peak congested travel time
AM_FLGCGSPDZERO AM peak congested speed is 0 indicator, 1 if speed is


AM_VCCAPRTO_10A AM peak V/C Ratio (same as VC_10A)
AL_VL_TOT_1A Daily time total volume for year 2010 and scenario


ALSLSL_VL_TOT_1A Selected Link Daily time total volume for year 2010

and scenario "A"

AL_VL_DA_10A Daily DA-Free&Toll-II&IE+EE traffic ALSL_VL_DA_10A Selected Link Daily DA-Free&Toll-II&IE+EE


AL_F_DA_10A Daily DA-II&IE-Free traffic ALSL_F_DA_10A Selected Link Daily DA-II&IE-Free traffic
AL_T_DA_10A Daily DA-II&IE-Toll ALSL_T_DA_10A Selected Link Daily DA-II&IE-Toll
AL_F_EDA_10A Daily DA-EE-Free ALSL_F_EDA_10A Selected Link Daily DA-EE-Free
AL_T_EDA_10A Daily DA-EE-Toll ALSL_T_EDA_10A Selected Link Daily DA-EE-Toll
AL_VL_SR2_10A Daily SR2-Free&Toll-II&IE+EE traffic ALSL_VL_SR2_10A Selected Link Daily SR2-Free&Toll-II&IE+EE


AL_F_SR2_10A Daily SR2-II&IE-Free ALSL_F_SR2_10A Selected Link Daily SR2-II&IE-Free
AL_T_SR2_10A. Daily SR2-II&IE-Toll ALSL_T_SR2_10A. Selected Link Daily SR2-II&IE-Toll
AL_F_ESR2_10A Daily SR2-EE-Free ALSL_F_ESR2_10A Selected Link Daily SR2-EE-Free
AL_T_ESR2_10A Daily SR2-EE-Toll ALSL_T_ESR2_10A Selected Link Daily SR2-EE-Toll
AL_VL_SR3_10A Daily SR3-Free&Toll-II&IE+EE traffic ALSL_VL_SR3_10A Selected Link Daily SR3-Free&Toll-II&IE+EE


AL_F_SR3_10A Daily SR3-II&IE-Free ALSL_F_SR3_10A Selected Link Daily SR3-II&IE-Free
AL_T_SR3_10A Daily SR3-II&IE-Toll ALSL_T_SR3_10A Selected Link Daily SR3-II&IE-Toll
AL_F_ESR3_10A Daily SR3-EE-Free ALSL_F_ESR3_10A Selected Link Daily SR3-EE-Free
AL_T_ESR3_10A Daily SR3-EE-Toll ALSL_T_ESR3_10A Selected Link Daily SR3-EE-Toll
AL_VL_TRK_10A Daily Truck-II&IE+EE+Port ALSL_VL_TRK_10A Selected Link Daily Truck-II&IE+EE+Port
AL_VL_PRTTK_10A Daily Port-Truck ALSL_VL_PRTTK_10A Selected Link Daily Port-Truck
AL_VL_EXT_10A Daily EXT-TRK + EE-Free&Toll(DA+SR2+SR3) ALSL_VL_EXT_10A Selected Link Daily EXT-TRK +


AL_VMT_10A Daily VMT
AL_VHT_10A Daily VHT
AL_CGTIME_10A Daily congested travel time, weighted average of four

time period

AL_CGSPEED_10A Daily congested travel speed
AL_VOLCNTRTO Old measure (obsolete)
AL_VCCAPRTO_10A Daily V/C Ratio



Redundant Steps

Several steps in the trip distribution part of the model are no longer needed.

Model operations previously used to combine trip tables are no longer necessary because DaySim uses its own set of procedures for creating trip tables from trip lists.

The pre-assignment step is now run only once, during the first feedback loop iteration. This is because the outputs from pre-assignment are used to build the transit network, which is only run during the first feedback loop iteration.

Clean up Cube Catalog Interface

The validation base year key (Valyear) is not read by the model and was removed from the catalog interface. All other keys in the interface are needed.

Performance Improvements

Table 7-2 shows the run times based on a 2015 vintage workstation with 8 logical processors before the changes were made and the run times after the changes, with various settings. Comparing the rows shaded in orange, the changes made to the model decreased the run time by more than 9 hours, a 44 percent improvement, for the base year model (2010), using the stricter relative gap and without path saving and select link analysis. The run of the same model with select link analysis for AM and PM periods and saving path file for AM period ran for 16:27, using the stricter relative gap, which is reasonable.

Table 7-2: Run time of the original and improved (V2) NERPMAB1v2 models Using a workstation with 8 logical processors

Table 7-2.png

New and Updated Scripts

Several new scripts were created and/or updated to support the listed changes. Table 7-3 shows the four scripts that are updated in the NERPMAB1v2 model, all corresponding to the highway assignments by time period. Table 7-4 presents the new scripts in the NERPMAB1v2 model with a brief description for each.

Table 7-3: Updated Scripts in the NERPMAB1v2 model

Table 7-3.png

Table 7-4: New scripts in the NERPMAB1v2 model

Table 7-4.png