Tier 2 Final Environmental Assessment I-66 Transportation Technical Report. Appendix E. Travel Demand Forecasting Model Validation Memorandum

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1 Tier 2 Final Environmental Assessment I-66 Transportation Technical Report Appendix E Travel Demand Forecasting Model Validation Memorandum FINAL AUGUST 216

2 MEMORANDUM To: Robert Josef, VDOT Northern Virginia Planning From: Stephen Weller, CH2M HILL Jennifer Martin, CH2M HILL Date: October 9, 214 (Updated July 16, 215) Subject: I-66 Corridor Travel Demand Forecasting Model Validation The Metropolitan Washington Council of Governments (MWCOG) travel demand model is the basis for travel forecasts for the I-66 Corridor Improvements Project. The I-66 model used Version 2.3, Build 52 of the MWCOG travel demand model as the starting point for the model to develop highway and transit forecasts for the corridor. The standard Version 2.3, Build 52 model was strategically modified with specific alterations to improve the accuracy and reliability of forecasts for the I-66 corridor, roadways connected to the corridor, and transit services in the vicinity of the corridor. The calibration targets are based on guidance from the Federal Administration (FHWA) Transportation Model Improvement Program (TMIP) Travel Model Validation and Reasonableness Checking Manual; and the Virginia Travel Demand Modeling Policies and Procedures Manual. Because the MWCOG/TPB Model is already subject to scrutiny as a regional model and has been a subject of FHWA s Travel Model Improvement Program (TMIP) Peer Review process, the validation process for the I-66 Interchange Justification Report (IJR) model focused on highway and transit assignment results. The analysis compares the model results to observed traffic counts, travel times, and transit ridership by time of day. Travel demand forecasting activity will be coordinated between the traffic and revenue study, IJR, NEPA effort, and transit studies in order to maintain consistency in forecasting among these efforts to the maximum extent practical. Alterations to the MWCOG travel demand model to improve corridor calibration included: network modifications to better represent study area facilities as they exist and are planned. Ramps are micro-coded to improve forecasts and correlation to the micro simulation process. Transit network modifications to better reflect existing and planned local and regional transit services and facilities. Forecasts from the travel demand model for local transit services were evaluated and model adjustments made as needed to improve the accuracy and reliability of forecasts in the corridor. Traffic Analysis Zone (TAZ) splits and centroid connector location changes to improve model loading for all modeled modes of transportation. Use of toll diversion methodology to forecast managed lane trips. 1

3 Changes to external trip assumptions to improve consistency with origin-destination data and traffic and revenue evaluations. Changes in the time-of-day distribution to improve forecasting of peak period trips, changes in the Delay Function (VDF) curves, and changes in the default speed and capacity of some facility types. Adjustments in the alternative-specific constant for commuter rail Home-Based Work (HBW) trips to improve the model representation of Virginia Railway Express (VRE) commuter rail service. Table 1 lists key assumptions associated with the travel forecasting process. Table 1: Travel Demand Forecasting Model Assumptions Model Parameter Assumption Model Analysis Years Time Periods Speed Link Capacity Peak Factors Value of Time (VoT) Socioeconomic Data 215 (Validation year) 225 (Opening year) 24 (Design year) Four time periods are modeled in the forecasts. The sum of the four time periods represents average weekday daily traffic: Period AM Midday PM Night Hours 6 a.m. 9 a.m. 9 a.m. 3 p.m. 3 p.m. 7 p.m. 7 p.m. 6 a.m. Consistent with current conditions in the HOV and General Purpose (GP) lanes. Lane capacities are defined consistently with the TPB/MWCOG model approach. The TPB/MWCOG facility and area type capacity tables are used to determine link capacities. The TPB/MWCOG model speed-flow curves retained in the I-66 Model. Peak period to peak hour factors: Period AM PM Existing peak period values were derived from the 27/28 MWCOG Household Travel Survey. The peak hour factors decline in future years in recognition of the increased congestion expected in the region, causing less-peaked periods. This assumption spreads the traffic evenly over the entire peak period. The VoT is based on the Tier II T&R study toll diversion curves developed for Office of Transportation Public and Private Partnerships (OTP3). VoT escalation assumptions will be consistent with OTP3 s consultant and will be made in consultation with the OTP3 s consultant and VDOT staff. MWCOG Round 8.3 socioeconomic data is used. Network Kimley-Horn/CH2M HILL 2 MEMORANDUM

4 General MWCOG Version with changes relating to FY TIP and Draft 214 CLRP publications on Air Quality Conformity Inputs (Draft dated 9/11/214). Project Description (I-66 Express Lanes) Project Extent I-495 to US 15 I-495 (Capital Beltway) HOV Transit Two managed lanes in each direction from I-495 to approximately US 15 in Haymarket. Specifics to be addressed in modeling effort. HOT (Express) lanes on I-495 at interchange with I-66 connecting to existing I-66 HOV lanes. Beginning in 22, all HOV facilities in the Northern Virginia area are assumed to become HOV-3+. Enhancements to the transit network to better reflect existing bus routes that would feed and/or operate within the managed lanes. Toll Assumptions Tolling Methodology Toll Approach Tolls Toll diversion curves (TDC) developed by OTP3 to be used in modeling for I- 95/395, I-495, and I-66 in the final assignment iteration. Variable toll rates by roadway segment, based on maintaining managed lane speed goal of 55 mph to account for varying demand levels along the length of the project. Toll rates will vary and be set to maintain minimum 45 mph speeds on the managed lanes and will be consistent with the assumptions made by OTP3 s consultant. Tolls will be charged at all times and be in place for both directions of the I-66 corridor. The modeled toll rates are not dynamic over each analysis period as would occur in reality but will be a representative average period toll. Mode Assumptions in I-66 Express Lanes Vehicle Class HOV Vehicles Hybrid/Violators Buses Transit Capacity Constraint HOV-3+: Free Other cars and medium trucks: Toll Heavy trucks: Not permitted in managed lanes Used the MWCOG model HOV module. Beginning in 22, all HOV facilities in Northern Virginia area will be HOV-3+. The HOV estimates provided are an output of the mode choice and carpool occupancy models developed by MWCOG. Modeled as a single class. Details to be developed in coordination with OTP3 s consultant and VDOT staff. Examined loading transit vehicles to highway networks in the I-66 corridor to account for transit usage on the managed lanes. Park-and-ride and kiss-and-ride access trips to park-and-ride lots will be included in the traffic assignment. Removed MWCOG model Metrorail transit constraint (constrains at 22 in base model). MODEL REMEDIATION ELEMENTS The model parameters and networks were adjusted to better align the study area traffic volumes with the peak and daily counts available. Analysis of the MWCOG model showed that the existing model performed reasonably well; however, it underestimated the amount of traffic occurring in the peak and was not capturing the appropriate differences in traffic on the different facilities. The regional model Kimley-Horn/CH2M HILL 3 MEMORANDUM

5 uses time of day factors by trip purpose to allocate daily trips to the four time periods. The four time periods in the MWCOG model are used in the I 66 model: AM Peak (6: 9: a.m. 3 hours) Midday (9: a.m. 3: p.m. 6 hours) PM Peak (3: 7: p.m. 4 hours) Night (7: p.m. 6: a.m. 11 hours) The MWCOG model was not validated to peak period count information. The regional model time-of-day factors are estimated based on travel survey information and, like most regional models, these factors are held constant once developed. The regional model time-of-day factors are generic, as one set of factors covers the entire modeling area. Because a specific study area will have trips that are distributed differently due to the traffic patterns of the study area, the time-of-day factors were adjusted to better align with traffic counts in the study area. The base and adjusted time-of-day factors are displayed in Table 2. The traffic analysis zones (TAZs) and the transportation network were inspected and modified to ensure that the model was accurately reflecting the existing network and to more accurately reflect the loading and access to the I-66 corridor. The TAZs were analyzed using the Prince William County and Fairfax County sub-models as a basis for disaggregating the MWCOG zone system. Zone splits were made when the access locations or nature of a zone indicated that better highway and transit loadings could be forecast. The study team analyzed approximately 2 zones in the corridor for zone-splitting potential. The I-66 model includes 21 zone splits resulting in 34 additional zones over the MWCOG model. Table 3 and Figures 1-8 show the zone splits in the corridor. The established socioeconomic data from the Round 8.3 adopted land use model files were disaggregated to the zone splits. Total population, households, and employment were maintained. Kimley-Horn/CH2M HILL 4 MEMORANDUM

6 Table 2: Base and Adjusted Time-of-Day Factors MWCOG V Time of Day I 66 T2/IJR Time of Day Purpose Mode Dir* AM MD PM OP AM MD PM OP HBW Auto Driver H >NH HBW Auto Driver NH >H HBW Drive Alone H >NH HBW Drive Alone NH >H HBW Carpool Rider H >NH HBW Carpool Rider NH >H HBW Transit H >NH HBW Transit NH >H HBW Auto Driver H >NH HBS Auto Driver NH >H HBS Drive Alone H >NH HBS Drive Alone NH >H HBS Carpool Rider H >NH HBS Carpool Rider NH >H HBS Transit H >NH HBS Transit NH >H HBO Auto Driver H >NH HBO Auto Driver NH >H HBO Drive Alone H >NH HBO Drive Alone NH >H HBO Carpool Rider H >NH HBO Carpool Rider NH >H HBO Transit H >NH HBO Transit NH >H NHB Auto Driver H >NH NHB Auto Driver NH >H NHB Drive Alone H >NH NHB Drive Alone NH >H NHB Carpool Rider H >NH NHB Carpool Rider NH >H NHB Transit H >NH NHB Transit NH >H NHO Auto Driver H >NH NHO Auto Driver NH >H NHO Drive Alone H >NH NHO Drive Alone NH >H NHO Carpool Rider H >NH NHO Carpool Rider NH >H NHO Transit H >NH NHO Transit NH >H *Direction H >NH=Home to non home, NH >H=Non home to home Kimley-Horn/CH2M HILL 5 MEMORANDUM

7 Table 3: Base TPB/MWCOG Zones Split for I-66 Corridor Model TPB/MWCOG Figure County New Zone Numbers Zone Number Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Fairfax Prince William Prince William Prince William Kimley-Horn/CH2M HILL 6 MEMORANDUM

8 Figure 1: Zone splits for MWCOG zones 1618 and 1656 Figure 2: Zone splits for MWCOG zones 1632, 1638, 1639, 1796, and 1797 Kimley-Horn/CH2M HILL 7 MEMORANDUM

9 Figure 3: Zone splits for MWCOG zones 1645, 1646, 1647, 1652, and 1654 Figure 4: Zone splits for MWCOG zones 1694, 1695, and 1699 Kimley-Horn/CH2M HILL 8 MEMORANDUM

10 Figure 5: Zone splits for MWCOG zones 185, 188, and 181 Figure 6: Zone splits for MWCOG zone 2468 Kimley-Horn/CH2M HILL 9 MEMORANDUM

11 Figure 7: Zone splits for MWCOG zone 2533 Figure 8: Zone splits for MWCOG zone 2554 and transit networks were adjusted to reflect the changes in the TAZs as well as refinements and adjustments to the network to accurately reflect the network. Network changes included adjusting zone centroid connections to improve the network loading, network refinements; corrections to properly represent the transportation supply; and to improve the correspondence between the micro simulation networks and the demand modeling networks. In many cases these changes to the network are Kimley-Horn/CH2M HILL 1 MEMORANDUM

12 deterministic, such as changing the number of lanes. The changes can also be qualitative, such as describing the facility in terms of operational and functional classification and the representative loading of zone centroid connectors. It is critical that these changes not be severe or arbitrary as that type of change may provide reasonable calibration to counts but will be totally ineffective in forecasting future travel activity. VALIDATION RESULTS The following tables and charts provide comparison results of the model performance to observed traffic data collected from various sources. The model results were compared to observed traffic data and evaluated based on guidance from the Federal Administration (FHWA) Model Reasonableness and Checking Manual 1 and the VDOT Virginia Travel Modeling (VTM) Policies and Procedures Manual 2. These metrics are calculated for the AM and PM peak periods and for the total day and they include: volume validation measures o Count to volume ratio over all counts segmented by facility type and period. o Root Mean Square Error (RMSE) of the counts versus the observed data. o R2 (coefficient of determination) for AM peak, PM peak and daily model to count relationship. o Visual analysis scatter plots of model volume versus observed volumes. screenline and cordon count validation measures o Summaries of count versus modeled traffic summaries across cutlines along the corridor for AM peak, PM peak, and daily loadings. travel time related validation measures o Comparison of model travel times to observed travel times. Transit measures o Comparison of assigned transit boardings to transit route counts by mode and station. The FHWA and VTM guidance do not specify criteria that imply a definition of acceptance of the model. Instead, the documentation provides guidance for the development of acceptable thresholds which must be balanced by data, resources, the goals and decisions that must be supported by the model. This section describes the targets and results of the performance measures for the I-66 model validation. Validation Measures Current FHWA guidelines do not specify a particular percent error by functional class, but instead display example validation standards from multiple states. Under both current VTM (page 62) and older FHWA (Table 9.2, page 9-19) guidelines, the guidance in overall deviation in traffic counts is based on daily VMT and is shown in Table 4. 1 FHWA Transportation Model Improvement Program (TMIP) Travel Model Validation and Reasonableness Checking Manual, Second Edition, Prepared by Cambridge Systematics, September 21 2 Virginia Department of Transportation, Virginia Travel Model (VTM) Policies and Procedures Manual Version 1.3, May 29. Kimley-Horn/CH2M HILL 11 MEMORANDUM

13 Table 4: Guidance on Percent Difference Targets for Daily VMT by Facility Type Facility Type FHWA Criteria VTM Acceptable Practice VTM Recommended Practice Freeways and HOV +/-7% +/-1% +/-5% Major Arterials +/-1% +/-15% +/-1% Minor Arterials +/-15% +/-2% +/-15% Guidelines set for RMSE in the VTM and FHWA documents are rather general and varied based on the midpoint of the link volume group or model region size. As with all model validation metrics, these are guidelines or thresholds, not standards that must be met, or, once they are met, indicates an acceptable model. Based on this information, the study team set a %RMSE goal to be below 3 percent on a daily basis and 4 percent for the peak periods. VTM (page 67) and FHWA (page 9-1) recommend a coefficient of determination of.9 and.88 between the observed data and the model results, although the FHWA Model Validation and Reasonableness Checking Manual suggests that this standard has little meaning for the validity of the model. Table 5 shows the number of count locations in the study area and the overall difference between the count locations with observed data and model results by facility type, as well as the %RMSE of the observed data versus the model results. Models generally do not perform well at lower facility classes. This is because there are many more alternate paths to use to access zone centroids. Also, there is a lower percentage of major and minor arterials counted compared to freeways in this corridor. The model may show under- or over-estimation compared to counts, but there may be other lower level facilities without counts balancing out the volume. Table 5 shows the I-66 model exceeds the FHWA acceptable criteria for percent difference in model versus observed count data for all facility types except the PM freeway, which is just beyond the recommended guideline. The I-66 model exceeds VTM recommended criteria for all facility types and time periods, except for PM freeways and PM and daily minor arterials. These groups that do not match the criteria are close to meeting them. The I-66 model exceeds the VTM Percent Root Means Square guidelines for all periods and facility types and exceeds by one percent the Percent RMSE value for daily traffic. Table 5: Number of Counts, Count to Model Comparison, and RMSE in Study Area I-66 T2/IJR Count - Comparison Number of Counts AM Period PM Period ADT Freeways & HOV Major Arterials Minor Arterials Collectors Ramps Total Number of Counts Kimley-Horn/CH2M HILL 12 MEMORANDUM

14 Count to Model Comparison AM Period PM Period ADT FHWA "Acceptable" Criteria and VTM Recommended Criteria: Freeways (FHWA +/- 7%; VTM +/- 6%) % 12% % Major Arterials (FHWA +/- 1%; VTM +/- 7%) 7% -2% 3% Minor Arterials (FHWA +/- 15%; VTM +/- 1%) 7% -7% -9% RMSE in Study Area AM Period PM Period ADT FHWA and VDOT Recommended Guidance: (Periods: <4), (Day: <3) %RMSE = VDOT Recommended Guidance (Freeways): (Periods: <3), (Day: <2) %RMSE Freeways VDOT Recommended Guidance (Major Arterials): (Periods: <45), (Day: <35) %RMSE Major Arterials VDOT Recommended Guidance (Minor Arterials): (Periods: <6), (Day: <5) %RMSE Minor Arterials Note: No guidance is explicitly provided by FHWA or VDOT for period validation. Note: Table 31 of the VTM Policy Manual provides VDOT guidance for RMSE by facility for small and large areas. Note: FHWA criteria was obtained from the Model Validation and Reasonableness Checking Manual Figures 9 and 1 are scatter plots of the observed count data versus the model volumes for the AM period. The AM period scatter plot shows a reasonable relationship between counts and modeled volumes. Figures 11 and 12 show similar plots for the PM peak period, while Figures 13 and 14 show the same plots for the daily loadings. Kimley-Horn/CH2M HILL 13 MEMORANDUM

15 Figure 9: AM Peak Period Scatter Plot 3, AM COUNT VS. MODEL VOLUME Model 2, 1, 1, 2, 3, Count Collector Ramps Minor Arterial Major Arterial Freeway Figure 1: AM Peak Period Low Scatter Plot Model 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 AM COUNT VS. MODEL VOLUME 5 1, 1,5 2, 2,5 3, 3,5 4, 4,5 5, Count Collector Ramps Minor Arterial Major Arterial Freeway Kimley-Horn/CH2M HILL 14 MEMORANDUM

16 Figure 11: PM Peak Period Scatter Plot 3, PM COUNT VS. MODEL VOLUME Model 2, 1, 1, 2, 3, Count Collector Ramps Minor Arterial Major Arterial Freeway Figure 12: PM Peak Period Low Scatter Plot Model 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 PM COUNT VS. MODEL VOLUME 5 1, 1,5 2, 2,5 3, 3,5 4, 4,5 5, Count Collector Ramps Minor Arterial Major Arterial Freeway Kimley-Horn/CH2M HILL 15 MEMORANDUM

17 Figure 13: Daily Period Scatter Plot 12, DAILY COUNT VS. MODEL VOLUME 1, Model 8, 6, 4, 2, 2, 4, 6, 8, 1, 12, Count Collector Ramps Minor Arterial Major Arterial Freeway Figure 14: Daily Period Low Scatter Plot Model 1, 9, 8, 7, 6, 5, 4, 3, 2, 1, DAILY COUNT VS. MODEL VOLUME 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, Count Collector Ramps Minor Arterial Major Arterial Freeway The VTM Policies and Procedures Guidelines recommend a coefficient of determination (R 2 ) of.9 between the observed data and the model results. The FHWA guidelines recommend a R 2 value of.88. Table 6 displays the R 2 for the AM peak, PM peak, and daily results. TheI-66 model exceeds the Kimley-Horn/CH2M HILL 16 MEMORANDUM

18 recommend R 2 for both larger areas (.9) and small areas (.92) on a daily basis. The model R 2 value is slightly below the VTM guidelines for the AM and PM periods. Table 6: Correlation Coefficient and Percent of Links within FHWA and VTM Recommended Standard Deviation for AM Peak, PM Peak, and Daily Coefficient of Determination (R 2 ) AM Period PM Period ADT FHWA Criteria (>=.88) VTM Criteria (>=.9) Note: The coefficient of determination (R 2 ) of.9 is obtained from Table 31 of the VTM Note: FHWA criteria was obtained from the Model Validation and Reasonableness Checking Manual Cutline Validation Measures While the aggregate statistics for the study area are very encouraging, additional analysis was needed to validate the model performance for specific geographic locations. Cutlines were developed based on count locations to allow for comparisons across the study area. Figure 15 displays the cutlines developed for the study area. Figure 15: Study Area Cutline Map Both FHWA and VTM have developed criteria for acceptance of screenline and cutline volumes in terms of maximum desirable percent deviation in total volumes. The curves used to determine the maximum desirable deviation are shown in Figure 16. Please note that these curves are developed for daily screenline and cutline volumes. Because the deviation is scaled with cutline volume, the maximum deviation is applied to the AM and PM peak periods as well as daily cutline results. Kimley-Horn/CH2M HILL 17 MEMORANDUM

19 Figure 16: Maximum Allowable Deviation in Total Cutline s Using VTM and NCHRP 255 Curves (from VTM Policy Manual, page 7) Maximum Allowable Deviation from Count 8% 7% 6% 5% 4% 3% 2% 1% % Maximum Allowable Deviation in Total Cutline Using VTM and NCHRP 255 Curves NCHRP 255 VTM Cutline Total Count Thousands Cutline Descriptions and Calibration Results Table 7 shows the aggregate cutline results for cutline modeled volume compares to observed traffic. Based on the curves in Figure 16, the cutlines meet or exceed FHWA criteria for cutlines in almost every instance (period and cutline combination). The cutlines meet or exceed the VTM criteria about half of the time on the corridor cutlines. The remainder of this section provides more detail on each individual cutline in the study area. Kimley-Horn/CH2M HILL 18 MEMORANDUM

20 Table 7: Cutline Summary for AM Period, PM Period, and Daily Model versus Observed Counts Cutline Name Num AM PM Daily Between US 15 (James Madison Hwy) and US 29 (Lee Hwy Gainesville) Between US 29 (Lee Hwy) and VA 234 Bypass (Prince William Parkway) Between VA 234 Bypass and VA 234 Business (Sudley Road) Between VA 234 Business and US 29 (Lee Hwy Centreville) Between VA 28 (Sully Road) and Stringfellow Road Between Monument Drive and US 5 (Lee Jackson Memorial Hwy) Between US 5 (Lee Jackson Memorial Hwy) and VA 123 (Chain Bridge Road) Between VA 123 (Chain Bridge Road) and Vaden Drive Between VA 234 (Nutley Street) and I-495 (Capital Beltway) Between I-495 and VA-7 (Leesburg Pike) 1 FHWA VTM 11 FHWA VTM 12 FHWA VTM 13 FHWA VTM 14 FHWA VTM 15 FHWA VTM 16 FHWA VTM 17 FHWA VTM 18 FHWA VTM 19 FHWA VTM Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria Does not exceed criteria 19

21 Cutline Name Between US 15 (James Madison Hwy) and US 29 (Lee Hwy Gainesville) Between US 29 (Lee Hwy) and VA 234 Bypass (Prince William Parkway) Between VA 234 Bypass and VA 234 Business (Sudley Road) Between VA 234 Business and US 29 (Lee Hwy Centreville) Between VA 28 (Sully Road) and Stringfellow Road Between Monument Drive and US 5 (Lee Jackson Memorial Hwy) Between US 5 (Lee Jackson Memorial Hwy) and VA 123 (Chain Bridge Road) Between VA 123 (Chain Bridge Road) and Vaden Drive Between VA 234 (Nutley Street) and I-495 (Capital Beltway) Between I-495 and VA-7 (Leesburg Pike) Number Table 8: Cutline Summary for AM Period Number of Counts Sum of Counts Sum of s at Count s / Count Ratio VDOT Criteria FHWA Criteria ,93 31, High (.21) Exceeds ,847 33, High (.14) Exceeds ,38 39, High (.2) Exceeds ,625 37, Exceeds Exceeds ,576 62,12.95 Exceeds Exceeds ,963 48, Exceeds Exceeds ,49 55, Exceeds Exceeds ,436 52,8.92 Exceeds Exceeds ,984 54, Exceeds Exceeds ,714 38, Exceeds Exceeds Combined Cutline Totals , , Kimley-Horn/CH2M HILL 2 MEMORANDUM

22 Table 9: Cutline Summary for PM Period Cutline Name Number Number of Counts Sum of Counts Sum of s at Count s / Count Ratio VDOT Criteria FHWA Criteria Between US 15 (James Madison Hwy) and US 29 (Lee Hwy Gainesville) ,614 46, High (.13) Exceeds Between US 29 (Lee Hwy) and VA 234 Bypass (Prince William Parkway) ,287 48, High (.7) Exceeds Between VA 234 Bypass and VA 234 Business (Sudley Road) ,152 57, Exceeds Exceeds Between VA 234 Business and US 29 (Lee Hwy Centreville) ,73 54, Exceeds Exceeds Between VA 28 (Sully Road) and Stringfellow Road ,284 94, High (.4) Exceeds Between Monument Drive and US 5 (Lee Jackson Memorial Hwy) ,591 7, Low (.4) Exceeds Between US 5 (Lee Jackson Memorial Hwy) and VA 123 (Chain Bridge Road) ,271 81, High (.4) Exceeds Between VA 123 (Chain Bridge Road) and Vaden Drive ,492 79, Exceeds Exceeds Between VA 234 (Nutley Street) and I-495 (Capital Beltway) ,14 79, Exceeds Exceeds Between I-495 and VA-7 (Leesburg Pike) ,17 58, High (.3) Exceeds Combined Cutline Totals ,668 67, Kimley-Horn/CH2M HILL 21 MEMORANDUM

23 Table 1: Cutline Summary for Daily Number of Counts Sum of Counts Sum of s at Count s / Count Ratio VDOT Criteria FHWA Criteria Cutline Name Number Between US 15 (James Madison Hwy) and US 29 (Lee Hwy Gainesville) , , High (.17) High (.5) Between US 29 (Lee Hwy) and VA 234 Bypass (Prince William Parkway) , , High (.4) Exceeds Between VA 234 Bypass and VA 234 Business (Sudley Road) , , Exceeds Exceeds Between VA 234 Business and US 29 (Lee Hwy Centreville) , , Exceeds Exceeds Between VA 28 (Sully Road) and Stringfellow Road ,27 337,41.96 Exceeds Exceeds Between Monument Drive and US 5 (Lee Jackson Memorial Hwy) , , Low (.8) Exceeds Between US 5 (Lee Jackson Memorial Hwy) and VA 123 (Chain Bridge Road) ,516 38, Exceeds Exceeds Between VA 123 (Chain Bridge Road) and Vaden Drive ,75 296,57.94 High (.1) Exceeds Between VA 234 (Nutley Street) and I-495 (Capital Beltway) , , High (.3) Exceeds Between I-495 and VA-7 (Leesburg Pike) , , High (.14) Exceeds Combined Cutline Totals 97 2,396,734 2,418, Kimley-Horn/CH2M HILL 22 MEMORANDUM

24 Cutline 1: This cutline is located between US 15 (James Madison Hwy) and US 29 (Lee Hwy Gainesville). This cutline includes Heathcote Blvd, I-66 mainline lanes, VA 55 John Marshall Hwy/ Washington St, and US 29 Lee Hwy. This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for cutlines for AM peak and PM peak, and does not exceed the FHWA Model Reasonableness and Checking Manual guidance for cutlines for daily nor the VTM guidance for cutlines for AM peak, PM peak, and daily. Figures show bar charts of the links crossing cutline 1 and the absolute difference of the link model volumes to observed count data for AM peak, PM peak, and daily. The model over-forecasts the I-66 mainline traffic and the peak direction on Heathcote Blvd. The over-forecasting on Heathcote Blvd is because the nature of travel demand models TAZ loading as discrete points. The forecasts for the daily volumes are higher than observed at this cutline location for both the eastbound and westbound directions, consistent with the peak period forecasts. Figure 17: Cutline 1 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Heathcote Boulevard Heathcote Boulevard I-66 I-66 55/John Marshall 55/John Marshall Figure 18: Cutline 1 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Heathcote Boulevard Heathcote Boulevard I-66 I-66 55/John Marshall 55/John Marshall 23

25 Figure 19: Cutline 1 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Heathcote Boulevard Heathcote Boulevard I-66 I-66 55/John Marshall 55/John Marshall Cutline 11: This cutline is located between US 29 (Lee Hwy Gainesville) and VA 234 Bypass (Prince William Parkway). Cutline 11 includes US 29 Lee Hwy west of University Blvd, I-66 Mainline and HOV lanes, and Wellington Rd. This cutline exceeds FHWA Model Reasonableness and Checking guidelines for AM peak, PM peak, and daily. The cutline volumes are above VTM guidance for AM peak, PM peak, and daily driven by the over-forecast volumes on I-66. Figures 2-22 show bar charts of the links crossing cutline 11. The model over-forecasts the AM I-66 eastbound and westbound mainline and HOV traffic. The PM forecasts are reasonably close the westbound mainline although the traffic forecast for the HOV lanes are above counts. The eastbound PM traffic forecasts exceed observed traffic counts. Figure 2: Cutline 11 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, I-66 I-66 Wellington Road Wellington Road Linton Hall Road Linton Hall Road Kimley-Horn/CH2M HILL 24 MEMORANDUM

26 Figure 21: Cutline 11 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, I-66 I-66 Wellington Road Wellington Road Linton Hall Road Linton Hall Road Figure 22: Cutline 11 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, I-66 I-66 Wellington Road Wellington Road Linton Hall Road Linton Hall Road *Note: Model volumes for facilities without counts are not summed in cutline totals Cutline 12: This cutline is located between VA 234 Bypass (Prince William Parkway) and VA 234 Business (Sudley Road). This cutline includes VA 234 Sudley Rd north of I-66 through the Manassas National Battlefield Park, I-66 Mainline and HOV lanes, and Balls Ford Rd. This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak, PM peak, and daily. The cutline fails to meet the VTM guidance criteria in the AM peak period but exceeds the criteria for PM peak period and daily. The maximum allowable deviation between model and counts for the AM period is 13 percent, and the AM model to observed ratio is 2 percent high. Figure 23 shows that the model is overestimating traffic on US 29 and I-66 eastbound in this period. Figures show that the model is overestimating traffic on I-66 in both directions on a daily basis. The model overestimates I-66 traffic in both directions in the AM period on both the mainline and HOV lanes. Kimley-Horn/CH2M HILL 25 MEMORANDUM

27 Figure 23: Cutline 12 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Rt 234 (NB) Rt 234 (SB) I-66 I-66 Balls Ford Road Balls Ford Road Figure 24: Cutline 12 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Rt 234 (NB) Rt 234 (SB) I-66 I-66 Balls Ford Road Balls Ford Road Kimley-Horn/CH2M HILL 26 MEMORANDUM

28 Figure 25: Cutline 12 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Rt 234 (NB) Rt 234 (SB) I-66 I-66 Balls Ford Road Balls Ford Road Cutline 13: This cutline is located between VA 234 Business (Sudley Road) and US 29 (Lee Hwy Centreville) and includes US 29 west of Stone Rd, I-66 Mainline and HOV lanes and VA-28 (Centreville Rd) south of I-66. This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance and VTM guidance for AM peak, PM peak, and daily. Figures show bar charts of the links crossing cutline 13 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. Figure 26: Cutline 13 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, I-66 I-66 28/Centrevil le Road 28/Centrevil le Road Kimley-Horn/CH2M HILL 27 MEMORANDUM

29 Figure 27: Cutline 13 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, I-66 I-66 28/Centrevil le Road 28/Centrevil le Road Figure 28: Cutline 13 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, I-66 I-66 28/Centrevill e Road 28/Centrevill e Road *Note: Model volumes for facilities without counts are not summed in cutline totals Cutline 14: This cutline is located between VA 28 (Sully Road) and Stringfellow Road (west of VA 287, Fairfax County Parkway). Cutline 14 includes VA 28 (Sully Rd) north of I-66, Walney Rd, Northbourne Dr, I-66 Mainline and HOV lanes, and US 29 Lee Hwy west of VA 28. This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak, PM peak, and daily. The cutline exceeds the VTM guidance in the AM peak and daily. Figures show bar charts of the links crossing cutline 14 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. The eastbound AM period HOV forecasted traffic volume is slightly higher than observed Kimley-Horn/CH2M HILL 28 MEMORANDUM

30 counts and the AM period mainline forecast traffic is slightly above counts, resulting in peak period I-66 AM eastbound forecasts being 2 percent from the observed counts. The PM westbound traffic forecast on the HOV lanes is above counts and the mainline is below counts. The aggregate I-66 mainline plus HOV lanes is within 5 percent of observed traffic counts. Figure 29: Cutline 14 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, 28/Centrevil le Road (SB) 28/Centrevil le Road (NB) Walney Drive (SB) Walney Drive (NB) Northbourn e Drive Northbourn e Drive I-66 I-66 Figure 3: Cutline 14 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, 28/Centrevil le Road (SB) 28/Centrevil le Road (NB) Walney Drive (SB) Walney Drive (NB) Northbourn e Drive Northbourn e Drive I-66 I-66 Kimley-Horn/CH2M HILL 29 MEMORANDUM

31 Figure 31: Cutline 14 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, 28/Centrevill e Road (SB) 28/Centrevill e Road (NB) Walney Drive (SB) Walney Drive (NB) Northbourne Drive Northbourne Drive I-66 I-66 Cutline 15: This cutline is located between Monument Drive and US 5 (Lee Jackson Memorial Hwy) and includes US 5 (Lee Jackson Memorial Hwy) near Fair Oaks Mall, I-66 Mainline and HOV lanes, Monument Dr, Government Center Pkwy, and US 29 (Lee Hwy). This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance and VTM guidance for AM peak, PM peak, and daily. Figures show bar charts of the links crossing cutline 15 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. The model over predicts traffic on I-66 at the cutline in the AM period. The PM westbound I-66 mainline traffic forecasts are 9 percent lower than observed counts. The combined mainline plus HOV modeled traffic is 1 percent from observed traffic counts. The daily modeled traffic volumes are 1.5 percent higher than counts in the eastbound direction and 3.5 percent higher in the westbound direction. Kimley-Horn/CH2M HILL 3 MEMORANDUM

32 Figure 32: Cutline 15 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Rt 5 Rt 5 I-66 I-66 Monument Drive Monument Drive Governmen t Center Governmen t Center US 29 US 29 Figure 33: Cutline 15 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Rt 5 Rt 5 I-66 I-66 Monument Drive Monument Drive Governmen t Center Governmen t Center US 29 US 29 Kimley-Horn/CH2M HILL 31 MEMORANDUM

33 Figure 34: Cutline 15 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Rt 5 Rt 5 I-66 I-66 Monument Drive Monument Drive Government Center Government Center US 29 US 29 Cutline 16: This cutline is located between US 5 (Lee Jackson Memorial Hwy) and VA 123 (Chain Bridge Road) includes CR 664 (Oakton Rd), I-66 Mainline and HOV lanes, VA 123 (Chain Bridge Rd), and US 29 (Lee Hwy). This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak, PM peak, and daily. The cutline exceeds the VTM guidance in the AM peak period and daily. The maximum allowable deviation between model and count is above the VTM criteria for PM peak period cutline traffic (suggested PM VTM deviation = 8.5 percent, model deviation from counts = 13 percent). The model overestimates traffic US 5 and US 29 in both the eastbound and westbound directions. It also overestimates the I-66 westbound traffic, while underestimating the eastbound (reverse peak) traffic on I-66. Figures show bar charts of the links crossing cutline 16 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. The model generally under-predicts traffic on I-66 cutline 16. In the AM peak period, the model traffic volume is 12 percent lower than observed counts. The PM peak period westbound traffic forecasts are 4 percent higher than observed counts and the PM period eastbound traffic is 1 percent lower than observed traffic counts. The daily modeled traffic volumes are 4 percent higher than observed counts in the westbound direction and 1 percent higher in the eastbound direction. Kimley-Horn/CH2M HILL 32 MEMORANDUM

34 Figure 35: Cutline 16 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Oakton Road Oakton Road I-66 I-66 US 123 US 123 Figure 36: Cutline 16 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Oakton Road Oakton Road I-66 I-66 US 123 US 123 Kimley-Horn/CH2M HILL 33 MEMORANDUM

35 Figure 37: Cutline 16 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Oakton Road Oakton Road I-66 I-66 US 123 US 123 Cutline 17: This cutline is located between VA 123 (Chain Bridge Road) and Vaden Drive. Cutline 17 includes VA 123 (Chain Bridge Rd) south of Jermantown Rd, Blake Ln, I-66 Mainline and HOV, and US 29/ 5 (Fairfax Blvd), Old Lee Hwy, and VA 236 (Main St). This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak, PM peak, and daily. The cutline exceeds the VTM guidance in the AM and PM peak period. The maximum allowable deviation between model and count is just above the VTM criteria for Daily cutline traffic (suggested Daily VTM deviation = 5 percent, model deviation from counts = 6.4 percent). Figures 38-4 show bar charts of the links crossing cutline 17 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. In the AM peak period, the model I-66 traffic volume is 11 percent lower than observed counts in the eastbound direction (mainline plus HOV) and 26 percent lower than counts in the westbound direction. The PM peak period westbound traffic forecasts are 12 percent higher than observed counts and the PM period eastbound traffic is less than 1 percent lower than observed traffic counts. The daily modeled traffic volumes are 6 percent lower than observed counts in the westbound direction and 9 percent lower in the eastbound direction. Kimley-Horn/CH2M HILL 34 MEMORANDUM

36 Figure 38: Cutline 17 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, US 123 (SB) US 123 (NB) Blake Lane Blake Lane I-66 I-66 Rt 5 Rt 5 Old Lee Hwy Old Lee Hwy VA 236 VA 236 Figure 39: Cutline 17 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, US 123 (SB) US 123 (NB) Blake Lane Blake Lane I-66 I-66 Rt 5 Rt 5 Old Lee Hwy Old Lee Hwy VA 236 VA 236 Kimley-Horn/CH2M HILL 35 MEMORANDUM

37 Figure 4: Cutline 17 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, US 123 (SB) US 123 (NB) Blake Lane Blake Lane I-66 I-66 Rt 5 Rt 5 Old Lee Hwy Old Lee Hwy VA 236 VA 236 *Note: Model volumes for facilities without counts are not summed in cutline totals Cutline 18: This cutline is located between VA 234 (Nutley Street) and I-495 (Capital Beltway) and includes CR 698 (Cedar Lane), Park St, I-66 Mainline and HOV, US 29 (Lee Hwy), and US 5 (Arlington Blvd.) This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak, PM peak, and daily. The cutline does not exceed the VTM guidance for Daily traffic. The maximum allowable deviation between model and count is above the VTM criteria for all periods (suggested daily VTM deviation = 5. percent, model deviation from counts = 7 percent). Figures show bar charts of the links crossing cutline 18 and the absolute difference of the link model volumes from, observed count data for AM peak, PM peak, and daily. In the AM peak period, the model I-66 traffic volume is12 percent higher than observed counts in the eastbound direction and 15 percent lower than counts in the westbound direction. The PM peak period westbound traffic forecasts are 2 percent higher than observed counts and the PM period eastbound traffic is less than.1 percent lower than observed traffic counts. The daily modeled traffic volumes are 3 percent higher than observed counts in the westbound direction and less than.5 percent higher in the eastbound direction. Kimley-Horn/CH2M HILL 36 MEMORANDUM

38 Figure 41: Cutline 18 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Cedar St (SB) Cedar St (NB) Park St Park St I-66 I-66 Rt 5 Rt 5 Figure 42: Cutline 18 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Cedar St (SB) Cedar St (NB) Park St Park St I-66 I-66 Rt 5 Rt 5 Kimley-Horn/CH2M HILL 37 MEMORANDUM

39 Figure 43: Cutline 18 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Cedar St (SB) Cedar St (NB) Park St Park St I-66 I-66 Rt 5 Rt 5 Cutline 19: This cutline is located between I-495 (Capital Beltway) and I-66/Leesburg Pike (VA 7). This cutline includes VA 7 (Leesburg Pike), VA 695 (Idylwood Rd), I-66 (HOV in peak direction inside I-495 (Capital Beltway)), and US 29 (Lee Hwy) immediately east of I-495 This cutline exceeds FHWA Model Reasonableness and Checking Manual guidance for AM peak period, PM peak period, and Daily. The cutline exceeds the VTM guidance in the AM peak period, but does not exceed the VTM criteria for the PM period and daily (suggested PM VTM deviation = 9.6 percent, model deviation from counts = 12. percent; suggested daily VTM deviation = 5.5 percent, model deviation from counts = 19 percent). Figures show bar charts of the links crossing cutline 19 and the absolute difference of the link model volumes from observed count data for AM peak, PM peak, and daily. On this cutline, inside the Beltway, the traffic counts are about half what they are outside the Beltway in part due to the HOV restrictions. In the AM peak period, the model I-66 traffic volume is 35 percent higher than observed counts in the eastbound direction and 16 percent lower than counts in the westbound direction. The PM peak period westbound traffic forecasts are 4 percent higher than observed counts and eastbound traffic counts are 3 percent higher than traffic counts. The daily modeled traffic volumes are approximately 16 percent higher than observed counts in the eastbound and westbound direction although the percent difference is higher because the observed count volumes are less than half the count volumes outside the beltway. Kimley-Horn/CH2M HILL 38 MEMORANDUM

40 Figure 44: Cutline 19 AM Period Count to Model Comparison by Facility 25, 2, AM Period Cutline Count to Model Comparison AM Count AM 15, 1, 5, Rt 7 Rt 7 I495 Offramp to Rt 7 Idylwood Idylwood I-66 I-66 Figure 45: Cutline 19 PM Period Count to Model Comparison by Facility 25, 2, PM Period Cutline Count to Model Comparison PM Count PM 15, 1, 5, Rt 7 Rt 7 I495 Offramp to Rt 7 Idylwood Idylwood I-66 I-66 Kimley-Horn/CH2M HILL 39 MEMORANDUM

41 Figure 46: Cutline 19 Daily Count to Model Comparison by Facility Daily Cutline Count to Model Comparison 12, 1, Daily Count Daily 8, 6, 4, 2, Rt 7 Rt 7 I495 Offramp to Rt 7 Idylwood Idylwood I-66 I-66 Travel Time Validation Measures There are no specified travel time validation measures in either the FHWA Model Reasonableness and Checking Manual or the VTM Policy Manual. The I-66 model output was compared to floating car travel time runs to ensure reasonable model performance when compared with observed travel times. Figures 47 and 48 depict the AM and PM peak travel times in the eastbound and westbound directions. These figures show the AM and PM eastbound model travel times and the minimum, maximum, and average observed travel times. The modeled AM and PM travel times are within the maximum and minimum travel times in most locations. The western most section which is has overestimated volumes in the model have higher travel times than observed in both peak periods (eastbound in the AM and westbound in the PM. Figure 47: Eastbound AM and PM Model Travel Times versus Observed Travel Times 6. Eastbound Travel Time 5. Travel Time (Minutes) to 66 OFF Rt 29 to 66 ON 286 to Rt 7 OVERPASS AM Time Period Minimum (minutes) AM Time Period Average (Minutes) AM Time Period Maximum (Minutes) AM Time Period Model Estimate PM Time Period Minimum (minutes) PM Time Period Average (Minutes) PM Time Period Maximum (Minutes) PM Time Period Model Estimate Kimley-Horn/CH2M HILL 4 MEMORANDUM

42 Figure 48: Westbound AM and PM Model Travel Times versus Observed Travel Times Travel Time (Minutes) Westbound Travel Time to 66 OFF Rt 28 (NB) to 66 OFF Rt 29 EB (2) to 66 Rt 245 AM Time Period Minimum (minutes) AM Time Period Average (Minutes) AM Time Period Maximum (Minutes) AM Time Period Model Estimate PM Time Period Minimum (minutes) PM Time Period Average (Minutes) PM Time Period Maximum (Minutes) PM Time Period Model Estimate Transit Validation Measures The model was adjusted to improve transit validation in the corridor. Initial examinations of the model showed that most aggregate transit service by mode was performing fairly well. The one transit service that was significantly under-represented was VRE commuter rail service. To account for this, the modespecific constant for Home-Based Work trips was adjusted to increase the number of trips in the commuter rail markets. Because we are focusing on the I-66 corridor, the validation tables focus on transit in the corridor and are not an attempt to validate the transit services across Fairfax and Prince William counties. Table 1 shows the model forecasts compared to the daily counts by service provider. The model slightly underestimates local bus service (Fairfax county Connector, Metrobus, and CUE service), but does a good job representing daily Metrorail and VRE services in the corridor. Table 11 shows the VRE modeled boardings by station. The model does not replicate specific station ridership, assigning more trips to the Manassas station, as opposed to the Broad Run and Manassas Airport stations. However, overall, the model is representing total VRE ridership on the Manassas line between Manassas and Rolling Road very well. Similarly, Table 12 shows the Orange Line station ridership in the corridor. The I-66 model accurately reflects the Metrorail ridership at a station level. The station modeled boardings vary by 1 percent to 16 percent from the observed boardings at Vienna, Dunn Loring, East Falls Church, and West Falls Church. The sum of the four stations modeled boardings are 5.8 percent higher than the observed daily boardings at these stations. Kimley-Horn/CH2M HILL 41 MEMORANDUM