TRAFFIC FORECAST METHODOLOGY

Transcription

1 CHAPTER 5 TRAFFIC FORECAST METHODOLOGY Introduction Need for County-Level Traffic Forecasting 2030 HC-TSP Model Methodology Model Calibration Future Traffic Forecasts Hennepin County Transportation Systems Plan (HC-TSP)

2 Chapter 5 Traffic Forecast Methodology 5.1 Introduction Literally millions of travel decisions are made on a daily basis in the Twin Cities metropolitan area. The travel demands that result from these decisions ebb and flow in a generally regular pattern that can be approximated by a computer model for analysis and evaluation. Computer models have very limited abilities to predict travel behavior. The flow of water in pipes or load carry capacity of beams in a structure follow known equations and these phenomena can be calculated with accuracy. In contrast, human drivers are sensitive to bottlenecks and congestion and their response is difficult to predict. Individuals often compensate in different ways by changing their travel route, combining trips, or adjusting the time of day when they travel. Historically, due to the sheer magnitude of the data and the required processing power, computer analysis was performed by the regional agencies of the Metropolitan Council and Mn/DOT. Advances in micro-computer technology since the early 1990 s have allowed these analysis to be performed by other agencies such as Hennepin County. This chapter documents the reasons behind why the computer analysis was brought in-house into the county in 1998, the methodology used to develop the traffic forecasting model for the 2030 HC-TSP, and the processes of calibrating the model to existing (2005) traffic counts and its use to forecast future traffic patterns to the year Need for County-Level Traffic Forecasting County-level in-house traffic forecasting was initiated by Hennepin County in 1998 because: There was a planning and design need for improved accuracy of traffic forecasts for the county s minor arterial roadways. Mn/DOT notified Hennepin County that they would no longer be providing detailed project forecasts. In-house modeling capabilities were available to develop and maintain a forecasting model. HC TSP 5-1 Chapter 5 Traffic Forecast Methodology

3 5.2.1 Need for Improved Accuracy The regional transportation forecasting model has been used and maintained by the Metropolitan Council and Mn/DOT over the last 40 years. Due to its regional perspective, the regional model utilizes socio-economic data (population, employment) for trip estimation and the roadway network is limited to the metropolitan highway system which includes principal arterials (interstate and state trunk highways) plus most minor arterial roadways. Due to this regional perspective, the Metropolitan Council and Mn/DOT have generally focused on the analysis of the principal arterials, with a lesser priority on the minor arterial system. A critical part of transportation modeling is the calibration of the model to existing traffic volumes and travel patterns. As the 2000 HC-TSP noted, the regional model has a high calibration accuracy for principal arterials and a lower accuracy for minor arterials consistent with the regional perspective. To obtain a high level of accuracy at the minor arterial level, Hennepin County needed to base trip estimation on land uses (use type and gross square footage) and expand the forecasting model to include most major and minor collector streets and to introduce detailed information from individual land use parcels Project Analysis Reports In 1998, Mn/DOT notified Hennepin County that they would no longer be able to provide project analysis reports to the county due to staffing limitations. These studies refined the regional traffic forecasts to provide peak hour turning movements necessary for project designs. An improved forecasting model was needed to provide the initial data for these analysis reports. There was also a similar need for information to evaluate large proposed developments and site plans that could potentially impact the county roadway system. The 2000 HC-TSP recommended implementing a project level analysis process in-house to replace the Mn/DOT reports. These reports were called SPARs for Special Project Analysis Reports, a nomenclature used by Mn/DOT. Since 2000, Hennepin County has produced dozens of these SPARs providing project level traffic forecasts. HC TSP 5-2 Chapter 5 Traffic Forecast Methodology

4 5.2.3 In-House Modeling Capabilities Staff expertise in the modeling area was expanded in the mid-1990 s. Staff enhanced their knowledge and understanding of micro-computer modeling by examining the modeling efforts of other agencies and studying the capabilities of new software packages that were being developed. In the late 1990 s, GIS was also being brought into the micro-computer environment, and these tools were used by county staff to complement the forecasting models HC-TSP Model Methodology To maintain consistency with the regional planning process, the 2030 HC-TSP forecasting model was developed within the original framework of the regional model. The existing regional model outside of Hennepin County was preserved as originally established by the Metropolitan Council and Mn/DOT. In this way the metropolitan model continues to be an integrated part of the 2030 HC-TSP refined forecasting model. Four-Step Modeling Process The 2030 HC-TSP continues the use of the 4-Step process similar to that used by the regional model. This process has been in use over the last 50 years for most of the large metropolitan areas in the United States. The 4-Step modeling process is deterministic, that is, it is assumed that the data inputs and model parameters are accurately known so that the result can be determined in a step-wise fashion. One of the challenges in this process is that the necessary data can be incomplete, and efforts must be made to estimate or collect additional data. HC TSP 5-3 Chapter 5 Traffic Forecast Methodology

5 The four steps of the process include: Trip Generation Travel Distribution Modal Split Network Assignment Trip Generation Trip generation is the estimation of how many trips are created and attracted within the county. To facilitate computer modeling, the trips are estimated for sub-areas call Traffic Analysis Zones (TAZ). The 2030 HC-TSP model currently has 1,474 TAZs. The original regional trip tables that quantify the trips between all TAZs were preserved for TAZs outside of Hennepin County. Trips that were originally estimated to travel from the county to elsewhere in the region or from the region to the county were extracted from the Metropolitan Council regional model for combining as part of the refinement process. The land use database mentioned in Chapter 3 was used for specific parcel development. The trip generation for each individual land use was estimated in the TransCAD software package using trip rates derived by information from the Institute of Transportation Engineers (ITE). Specifics regarding this process are contained in the support documents. Exhibit 5-1 shows TAZs that were found to generate a significant difference in vehicle trips from Travel Distribution Travel distribution is the process by which the computer links the trips from the trip generation process and creates a TAZ trip table showing the trip interchanges between every pair of TAZ. The TransCAD model was used to take the trip generation estimates and develop the Average Daily Traffic (ADT) trip tables. Model parameters and assumptions used by the regional model were maintained for the travel distribution process of the 2030 HC-TSP. HC TSP 5-4 Chapter 5 Traffic Forecast Methodology

6 Exhibit 5-1 TAZ Comparisons of Trip Generation Change Modal Split The modal split process estimates the number of trips occurring on transit and assigns these trips using a transit modeling system. The remaining vehicle trips are assigned to a roadway network for traffic volume tabulation. Estimates from the Met Council regional model were used for the 2005 trip generation. The future Met Council transit estimates were also incorporated by employing a factoring methodology for the vehicle trip tables. Inclusion of the regional future transit assumptions means that the modeling incorporates the projection that transit trips will double from today to the year This anticipated increase in transit patronage is reflected in higher zonal interchange factors along future transit corridors for LRT and BRT. These factors result in a reduction of future vehicle trips. As with the regional model, the modeling does not include pedestrian and bicycle trips. These types of trips are generally made for short distances, tend to occur within the same model TAZ, and their volumes are difficult to forecast with any HC TSP 5-5 Chapter 5 Traffic Forecast Methodology

7 level of accuracy. The planning for facilities for these types of trips is covered in the Hennepin County Bicycle Transportation Plan. Network Assignment The last step in the modeling process is the assignment of trips from the trip tables to the computerized roadway system. Basically this process is one of tabulating trips from the various zones as they are assigned to particular travel paths through the network. The computerized roadway system includes all Hennepin County roadways and all local Municipal State Aid (MSA) streets. In addition to all principal and minor arterial roadways, the system includes most major collector type streets and many minor collectors. 5.4 Model Calibration Model calibration is the process of refining and adjusting the model so that the initial base traffic assignment best reflects the observed traffic counts and travel patterns. Comparisons were made at almost 6,600 different Mn/DOT, Hennepin County, and MSA count locations. The outputs of the 2005 assignment from the 2030 HC-TSP model were compared to these actual 2005 counts. A total of 52 trial assignments or iterations were made to calibrate the model. Numerous corrections and refinements were needed during the calibration phase. These refinements included modifying items such as the roadway network configuration and the TAZ trip generations for particular zones. By iteration 40, all refinements were finalized, and the remaining corrections were made by systematically modifying the speeds of the network links. Exhibit 5-2 shows the distribution of deviation of the assignment to the actual counts for the observed network links. A discernable pattern can be seen from iteration 40 to iteration 52 where the initial goal posts of a high number of links that were significantly different to the counts, is slowly molded into a bellshaped curve at the final iteration 52. An empirical formula has been developed to measure a model s estimation performance to determine how many roadway lanes are required. The National Cooperative Highway Research Program (NCHRP) developed this function. A lower accuracy percentage is required at low actual volumes since a high percentage deviation does not affect the number of lanes needed. HC TSP 5-6 Chapter 5 Traffic Forecast Methodology

8 Exhibit 5-2 Status of the HC-TSP Model Calibration For example, the forecast for a roadway that actually carries 1,000 ADT could be off 70 to 80 percent (range of 200-1,800 ADT), and yet the lane needs would still be a 2-lane roadway. Conversely, a forecast for a high-volume highway carrying 100,000 ADT would need to be within approximately plus or minus 15 percent (range of 85, ,000) since a greater variation would change the lane needs significantly from a 6-lane highway to a 4-lane or an 8-lane highway. The NCHRP calibration criteria were applied to the 2030 HC-TSP model to evaluate the status of the calibration to 2005 counts. Over 93percent of the network links on the Mn/DOT and county roadway systems were found to be within the NCHRP bounds. This level of accuracy means that the 2030 HC-TSP model for 2005 is adequate to be used for the evaluation of county roadway lane needs. 5.5 Future Traffic Forecasts Estimations of future trips were made based on the future land use information from the cities described in Chapter 3. The total forecasted growth in trips resulting from the future land uses is shown in Table 5-1. The annual growth in trips is expected to decrease significantly based on the characteristics of the land use growth and increased transit and non-motorized usage. HC TSP 5-7 Chapter 5 Traffic Forecast Methodology

9 Table 5-1 Hennepin County Forecasted Growth in Vehicle Trips Year Vehicle Trips Annual Growth Rate ,220, ,740, percent/year (1995 to 2000) ,675, percent/year (2000 to 2005) ,140, percent/year (2005 to 2030) The future trips were assigned to a future roadway system that was comprised of improvements from the following elements: Hennepin County CIP Funded Projects Hennepin County CIP Provisional Projects Metropolitan Council Transportation Improvement Program (TIP) Mn/DOT Transportation Systems Plan (TSP) Mn/DOT Inter-regional Corridor Studies Selected improvements recommended by recent Transportation Studies (NW Hennepin Study, TH 610 Study, selected City traffic studies, etc.) Table 5-2, Table 5-3, and Table 5-4 itemize the specific roadway improvements that were included in three roadway networks that were studied; 2008 Network, Base 2030 Network, and the Optional 2030 Network. These improvements were included for modeling purposes, and not as a comprehensive listing of all future roadway projects. The three study networks are: 2008 Network This roadway network included all projects constructed since the base study year of 2005, plus those projects currently under construction. HC TSP 5-8 Chapter 5 Traffic Forecast Methodology

10 Base 2030 Network This network includes roadway elements that are anticipated to be implemented by 2030 due to their inclusion in CIP s, the TIP, or some action that makes the improvement likely. Optional 2030 Network This roadway network incorporates some roadway elements that have been proposed by this and other studies and are still under evaluation. Map C in the rear pocket of this report shows the Forecasted 2030 Average Daily Traffic (ADT). This information is used later for roadway system evaluation in Chapter 9. As was noted in the discussion of the model calibration above, the accuracy of the 2030 ADT forecasts are adequate for the basic determination of future lane needs. More detailed evaluations for details such as intersection geometrics and level of service are accomplished in the project level SPAR reports which concentrate on peak hour traffic characteristics. HC TSP 5-9 Chapter 5 Traffic Forecast Methodology

11 Table Roadway Network (Itemized Improvements) Roadway Termini City Mn/DOT I-35W UPA Project Lane Additions Minneapolis I-494 I-394 to TH 100 Mntka / EP / Blmgtn Trunk Highway 12 Highway 12 Bypass project Long Lake / Orono Trunk Highway 62 Crosstown Commons I-35W construction Mpls / Richfield Trunk Highway 100 Interchange revisions at Trunk Highway 7 St. Louis Park Trunk Highway 100 Lane additions: 36 th St. to Cedar Lake Rd. St. Louis Park Trunk Highway 212/312 Completion of TH 212 and TH 5 revisions Eden Prairie Hennepin County CSAH 10 (Bass Lake Road) Reconstruct Wedgewood Ln. to Vicksburg Ln. Maple Grove CSAH 30 Reconstruct Dunkirk Lane to CSAH 101 Maple Grove CSAH 61 (Shady Oak Rd.) Reconstruct Bren Road to CSAH 3 (Excelsior) Minnetonka CSAH 81 (Bottineau Blvd.) Reconstruct part of TH 610 construction Maple Grove CSAH 101 Reconstruct TH 7 to CSAH 5 (Mntka Blvd.) Minnetonka CSAH 121 (Tilden Connection) New roadway French Lake Rd to TH 169 Champlin CSAH 121 Realignment & vacation Elm Creek / Hayden Champlin Local Projects 99 th Avenue New Street - Maple Grove Pkwy to CSAH 121 Maple Grove Maple Grove Pkwy / Upland Ln New Street plus interchange with I-94 Maple Grove HC TSP 5-10 Chapter 5 Traffic Forecast Methodology

12 Table 5-3 Base 2030 Roadway Network (Itemized Improvements) Roadway Termini City Mn/DOT I-94 Lane Additions:- TH 610 to TH 101 Maple Grove Trunk Highway 101 Conversion to limited access north segment Rogers / Hassan Twp Trunk Highway 169 CSAH 30 / TH 610 / 101 st interchanges Brooklyn Park Trunk Highway 169 CSAH 81/CSAH 109 (85 th Ave) Devil s Triangle Brooklyn Park Trunk Highway 252 Roadway upgrade to limited access Brooklyn Center / BP I-494 Lane Additions: E. Bush Lake to 34 th Ave. Bloomington I-494 Lane Additions: I-94 to TH 55 Maple Grove / Plymouth I-494 / TH 169 Reconstruct interchange Bloomington Trunk Highway 610 Completion of highway from TH 169 to I-94 Maple Grove / BP Hennepin County CSAH 1 (Pioneer Trail) Reconstruct road from CSAH 4 to old TH 212 Eden Prairie CSAH 1 (Pioneer Trail) Reconstruct & add lanes: Co. limits to CSAH 4 Eden Prairie CSAH 10 (Bass Lake Road) Realign & add lanes: Vicksburg to Peony Maple Grove CSAH 10 / CSAH 101 Realign & add lanes: new intersection Maple Grove CSAH 14 (Douglas Drive) Reconstruct & add lanes: 109 th Ave. to CSAH 12 Champlin CSAH 24 Reconstruct & add lanes: east of CSAH 101 Plymouth CSAH 101 Reconstruct & add lanes with Stone s Throw Hassan Township CSAH 101 Reconstruct & add lanes: CSAH 6 to CSAH 24 Plymouth CSAH 101 Reconstruct & add lanes: TH 7 to CSAH 62 Minnetonka CSAH 101 Extension of Peony Lane to Lawndale / CR 47 Plymouth CSAH 103 (West Broadway) Reconstruct from CSAH 30 to CSAH 109 Brooklyn Park CSAH 109 (85 th Avenue) Add lanes Main Street to Jefferson Hwy Maple Grove County Road 116 Fletcher Bypass extension to CSAH 81 Rogers / Hassan Twp County Road 117 Road extension from CR 116 to CSAH 101 Hassan / Corcoran CSAH 122 (Washington Ave.) Reconfigure for LRT at U of M Minneapolis County Road 159 Realignment east of CR 116 for Stone s Throw Hassan Township HC TSP 5-11 Chapter 5 Traffic Forecast Methodology

13 Table 5-4 Optional 2030 Roadway Network Roadway Termini City Mn/DOT Rogers I-94 / TH 101 New directional interchange Hennepin County Greenfield CSAH 30 New Crow River Bridge to Wright Co CR 144 Maple Grove TH 610 Extension Connection from I-94 to CSAH 30 HC TSP 5-12 Chapter 5 Traffic Forecast Methodology