Year 2007 Model Network

In order to update the year 2000 model network to the year 2007, a list of capacity-adding transportation improvements completed between the years 2001 and 2007 was developed and distributed to the ICC for review and approval. Maps of these projects and the corresponding list are included in Appendix A. These projects were coded on top of the previously validated 2000 model network to reflect 2007 transportation network conditions.

Maps of the 2007 model network by area type, facility type, and number of lanes also are included in Appendix B. As part of the 2007 model update, a new area type code representing industrial land uses were added to the model. This new area type provided the ability to reduce speeds in areas serving industrial facilities. The TPO conducted a windshield survey in 2008, during which time areas representing industrial land uses were noted and revised accordingly in the 2007 model. In addition, topography data was overlayed on top of the 2007 model network to assist with updating the mountainous area type codes added during the previous model/LRTP update.

As part of the 2007 model update and Congestion Management Plan Update, the TPO identified locations along CMP routes and in the 2007 model where additional counts were needed. The TPO collected these supplemental counts in 2008 to assist with validation. As a result, year 2007 traffic counts available from TDOT, GDOT, Hamilton County, and the City of Chattanooga were included in the 2007 traffic count field used to calculate validation statistics. However, a year 2008 traffic count field was added to the model network to include these supplemental traffic counts collected in 2008. Since the base year of the model was 2007, these 2008 counts were not included in the validation statistics. However, they were used to supplement validation efforts and compare to 2007 traffic counts for accuracy.

2.1 External Trips

As noted in technical submittal #2, eight new external stations were added to the 2007 model above and beyond the 30 external stations included in the previous 2000 model. Year 2007 traffic counts at each of the 38 external stations were utilized to determine the total external trips. The same percent distribution of external-external (EE), or through trips, versus internal-external (IE) trips at each of the original 30 internal-external zones used in the 2000 model was used for the 2007 model. Since the eight new external stations in the 2007 model were located along minor facilities, it was assumed that 100 percent of the external trips were attributed to IE trips, or those with one trip end inside the TPO region and one trip end outside the TPO region.

2.2 Trip Generation

Trip production rates utilized in the 2007 model are the same as those utilized in the 2000 model, as trip production rates were developed using local data from the Chattanooga 2002 Household Travel Diary Survey. However, trip attraction rates were modified in the 2007 model as they were borrowed from the Jacksonville, Florida region for the previous 2000 model.

Trip attractions for some purposes, such as Home-Based Work (HBW), differed appreciably from the trip productions and it was therefore decided to borrow trip attraction rates from the Knoxville model and adjust where appropriate in an attempt to achieve closer matches.

Utilizing Knoxville trip attraction rates is likely more appropriate for the Chattanooga region due to potential differences in travel characteristics in the Jacksonville, Florida region. The Knoxville trip attraction rates documented in the Knoxville Regional Travel Demand Model Validation Report of March 2004 resulted in some improvement in the unbalanced ratios for most trip purposes in Chattanooga. Adjustments were necessary to some of the trip attraction rates as trip purposes did not correlate perfectly between the Knoxville and Chattanooga models. The final Chattanooga 2007 model trip production and attraction rates are listed below.

Total Households Total Employment Agricultural / Mining / Construction Manufacturing / Transportation Retail Service Government School Enrollment Total Population

As demonstrated in Table 2, there were approximately nine person trips per household in the Chattanooga region in the 2007 model, within TDOT’s target range of 8.5 to 10.5, also comparing favorably with other cities in the region. Other aggregate trip rates are shown in Table 2 below.

Table 2. Aggregate Trip rates

Chattanooga Standards

Unit of Measure 2007 2000 TDOT FHWA

Persons per Household 2.38 2.50 n/a n/a

Internal Trips per Household 9.00 9.44 8.5-10.5 8.0-14.0 Internal Trips per Person 3.78 3.78 n/a 3.5-4.0

Home-Based School, Shopping, Social Recreation, and Other trips purposes. This is comparable to Nashville, Tennessee and Montgomery, Alabama at approximately 39 percent. Nonhome-Based (NHB) trips are within the desired range of 22 to 31 percent at 27 percent. Commercial vehicles represent approximately seven percent of the trips in the 2007 model, a reduction compared to the 2000 model. It must be noted, however, that employment in the 2007 model is lower than for the 2000 model, contributing to the reduced commercial vehicles, as demonstrated in technical submittal #2.

Table 3. Percent of Trips by Purpose

Chattanooga

Purpose 2007 2000 TDOT Target

Home-Based Work 13.23% 12.72% 18-27%

Home-Based School 5.31% 5.10%

Home-Based Shop 10.17% 9.56%

Home-Based Social Recreation

6.22% 5.57%

Home-Based Other 18.10% 17.33%

47-54%

Nonhome-Based 26.64% 26.06% 21-31%

Commercial Vehicles 7.38% 9.80%

Light-Truck 72.85% 73.65%

Medium-Truck 19.82% 19.34%

Heavy-Truck 7.33% 7.02%

Internal-External 11.08% 13.85%

External-External 1.86%

Total 100.00% 100.00%

2.3 Trip Distribution

Initially, friction factors from the previous 2000 model, which were borrowed from the earlier MINUTP model, were used as part of the validation of the 2007 model. However, upon review of the average trip lengths, it was determined that adjustments to the friction factors were necessary. As a result, the TPO first developed and calibrated new friction factors to match the Chattanooga 2002 Household Travel Diary Survey data. However, these new friction factors resulted in unsatisfactory results. Average trip lengths were proving to be shorter than expected and overall validation results were consequently worse. As a result, the original friction factors from the previous 2000 model were iteratively adjusted to achieve better trip

of this submittal.

Just as was included in the previous 2000 model, K-factors were necessary between areas north and west of the Tennessee River and areas south and east of the Tennessee River, as well as between Georgia and Tennessee. However, unlike the previous model, the K-factors were not directionally skewed to/from Georgia and Tennessee. In addition to the K-factors (0.8 for each), it was found necessary to add penalties, primarily along the Tennessee River bridges to correct local imbalances. Table 4 below lists the locations and amount of the penalties.

Table 4. Penalties

Roadway Penalty (minutes)

U.S. 27 Bridge 1.35

N. Market Street Bridge 1.10

Dupont Parkway 0.25

Mountain Creek Road 2.00

Table 5 demonstrates the final average trip lengths for each trip purpose in comparison to the old 2000 model. In addition, year 2007 Home-Based Work (HBW) trip lengths were compared to those included in the Census Transportation Planning Package (CTPP) for the year 2000 in Hamilton, Catoosa, and Walker Counties. HBW trip lengths improved in the 2007 model compared to the 2000 model as they are closer to the CTPP trip lengths. However, the 2007 model HBW trip lengths are still slightly shorter when compared to the CTPP trip lengths. This is as a result of the daily nature of the model compared to the highly peak hour weighted CTPP figure. The modest expansion of the model to include all of Catoosa County since the last LRTP partially explains the reduction in Internal-External trip times. All of the 2007 trip lengths are within acceptable limits provided by the Federal Highway Administration (FHWA). No trip length targets have been established by TDOT at this time.

The 2007 model validation effort involved significant splitting of zones, particularly towards the periphery. This reduced the average size of zones. Consequently, as indicated in Table 6, the percent intrazonal trips fell slightly to below nine percent as compared to above nine percent for the 2000 model. As expected, given the tendency of individuals to travel further for work purposes, the percent intrazonal trips for HBW are lower than for other purposes at just under two percent.

2007 2000

Light-Truck 17.78 18.79 Medium-Truck 17.20 17.95 Heavy-Truck 20.75 22.17

Internal-External 37.38 41.04 n/a n/a n/a n/a

Total 14.53 18.68 n/a n/a n/a n/a

Table 6. Intrazonal Trips by Trip Purpose

Chattanooga (TransCAD) Percent Intrazonal

Purpose 2007 2000

Home-Based Work 1.93% 7.04%

Home-Based School 6.63% 11.12%

Home-Based Shop 12.51% 9.93%

Home-Based Social Recreation

11.98% 21.08%

Home-Based Other 12.96% 11.16%

Nonhome-Based 9.61% 8.02%

Commercial Vehicles 2.77% 3.06%

Light-Truck 2.74% 2.95%

Medium-Truck 3.46% 4.15%

Heavy-Truck 1.27% 1.19%

Total 8.89% 9.18%

component. At the beginning of the 2035 LRTP Update, the RPA intended to add transit to the TransCAD model contingent upon the availability of existing data to validate the new transit component. However, upon review of the data, it was determined that an on-board transit survey was needed in order to validate a new transit model. The RPA will be developing the survey instrument for the on-board transit survey shortly after the adoption of the 2035 LRTP Update. Subsequently, the RPA will conduct the on-board survey in the Fall of 2010, in preparation for the next base year 2010 model for the LRTP Update to be adopted in 2014. The RPA intends to add the transit network/pathbuilding component to the next generation of the TransCAD model in time for the next LRTP update. In the interim, the same auto occupancy model used in the model from the previous 2030 LRTP Update is being used for the current 2035 LRTP Update. Ratios of persons per vehicle were derived from the local household diary survey conducted in the Chattanooga region in 2002.