California Department of Transportation GIS/Level of Service Application

 

Carlos P. Yamzon

Ty Phimmasone

 

 

ABSTRACT

 

This GIS application utilizes ArcView 3.2 Avenue programming to perform Highway Capacity Manual (HCM) capacity and levels of service analysis methodologies for freeways, multi-lane highways, and two-lane rural highways on the entire or selected segments of a Regional Traffic Model network. Using the ArcView and TP+ Plus/Viper software interface capabilities, a traffic model is converted to a shapefile and analyzed in the ArcView environment. This application demonstrates a GIS/Traffic Model/HCM Interface capability that streamlines the process of impact analysis on highway projects and local development.

 

 

 

INTRODUCTION

 

Transportation Planners utilize traditional, four-step models to translate indicators of travel demand developed from land use information to distribute, and assign trips to paths on highway or transit networks. The use of transportation models to support long-term planning activities associated with the development of Regional Transportation Plans (RTP), or other elements of long range improvement plans, has been an important tool in Transportation Planning.

 

The advances in computer technology have literally brought the four-step model, out of the “black box” syndrome, and many commercial packages include very advanced ‘state of the art” graphics capabilities that allow the user to develop very sophisticated network maps, within the program itself. Even with this improvement, many transportation modeling programs still include a GIS module that allows the integration of the transportation network with a GIS map. This allows the user to create a shapefile, and combine the analytical dynamics of a transportation model with GIS technology, to further enhance viewing, analyzing, processing, and presentation capabilities.

 

 

BACKGROUND

 

The California Department of Transportation (Caltrans) GIS/Level of Service Application was initiated as a pilot project funded by a Federal grant through Caltrans, to the Merced County Association of Governments (MCAG), a San Joaquin Valley Metropolitan Planning Organization (MPO).  The project focused on the development of interface capabilities between the MCAG Regional Transportation Model, and their extensive Geographical Information System (GIS) Program. The immediate applications of this interface were to enhance the ability of Caltrans to use the model in the development of traffic studies, in support of State Highway System (SHS) transportation project development in Merced County.

 

The traditional traffic forecasting and analysis procedures performed by Caltrans staff, entailed the use of the MCAG model as the source for future Average Daily Traffic (ADT) volumes, but the more detailed portion of the traffic studies required post-processing the majority of the remaining forecasting and operational analysis work. This was necessary because the regional priorities of the MPO model, and associated performance measures, did not translate directly to project level measures of effectiveness, that included very specific hourly traffic information, and adjustment factors required for the design of SHS projects. In addition to this, the model was based on a 25 year forecast consistent with MCAG’s Regional Transportation Plan (RTP), while Caltrans projects, although based on a 20 year design, had varying starting construction years, depending on transportation funding cycles.

 

 

OVERVIEW OF THE PROJECT

 

The California Department of Transportation (Caltrans) GIS/Level of Service Application (CTGLA) utilizes ArcView 3.2 Avenue programming to perform capacity and levels of service (LOS) analysis methodologies for freeways, multi-lane highways, and two-lane rural highways on the entire or selected segments of a transportation model network. These methodologies are based on procedures documented in the 1997 Highway Capacity Manual-Special Report 209 Third Edition (HCM). This GIS/LOS application specifically accepts a shapefile created in the Viper (Visual Planning Environment) program developed and distributed by the Urban Analysis Group/Citilabs Company. The GIS Tools (Optional Add-On Module) in the Viper program consist of a number of functions that allow the integration of the transportation model network with a GIS map. The CTGLA accepts the shapefile created by Viper, utilizing all available attributes of the transportation network, as the information source to perform LOS analysis in the ArcView environment.

 

Capacity analysis, is described in the 1997 Highway Capacity Manual- Special Report 209 Third Edition (HCM) as a set of procedures for estimating the traffic carrying ability of facilities over a range of defined operational conditions. The concept of level of service (LOS) is also described in the HCM, as qualitative measures that characterize operational conditions within a traffic stream and their perception by motorist and passengers. Levels of service are generally given letter designations with LOS A representing the best operating conditions and LOS F the worst.

 

Since this project was initiated, the HCM has been updated with minor changes to the freeway and multi-lane highway methodologies, and a completely new methodology of evaluating two-lane highways by direction of travel or by both directions combined. Although the process has started to update the Avenue programming, the CTGLA as presented at the 2002 Esri International User Conference, has not been modified to reflect the new truck equivalency factors for freeway and multi-lane highways, or the new methodologies for two-lane highways. 

 

For the purpose of the CTGLA, the analyses of three classes of roadways were selected. These were basic freeway segments, two-lane highways, and multi-lane highways. These roadways represented approximately 90 percent of the SHS in Merced County. Signalized intersections were not included in this pilot project because of the complexities associated with the analysis of facilities with interrupted flow conditions, and signal timing procedures.

 

The following examples identifies the roadway information, including notes on items specific to the MCAG project model, used in the Avenue programming, consistent with HCM methodologies for the specific CTGLA project application:

 

 

DEFINITION OF CLASSES:

 

FREEWAYS-                   Interstate 5 and State Route 99

TWO-LANE HIGHWAYS-         State Routes 140, 152 thru Los Banos, 165, 59, 33

MULTILANES-              State Route 152 outside of Los Banos

 

 

L.O.S. CALCULATION FOR FREEWAY:

 

  1. HEAVY VEHICLE FACTOR:               FHV = 1 / [1 + Pt (Et – 1)]

1.      Et (Terrain Factor)                             Look up in TABLE 3-3

  1. PEAK HOUR DIRECTIONAL VOLUME:     PHDV = Aadt * Ds * Factor

1.      Be cautious, the Aadt is the “TOTAL” volume. For roadways that are split into single-directional segments (in the cases of Interstate 5 and State Route 99) and the REV item is equal to 1, then the adjacent pieces must be summed to produce this “TRUE” Aadt.

  1. SERVICE FLOW:                                  Sfe = Msei * NoLanes * FHV

1.      If NoLanes = 2 (Per Direction) then      Msei = 2200

2.      If NoLanes = 3 (Per Direction) then      Msei = 2300

  1. CAPACITY:                                           C = PHDV / Sfe
  2. LEVEL OF SERVICE (L.O.S.):             Look up in TABLE 3-1

 

 

L.O.S. CALCULATION FOR TWO-LANE HIGHWAY:

 

  1. HEAVY VEHICLE FACTOR:               FHV = 1 / [1 + Pt (Et – 1)]

1.      Et (Terrain Factor)                             Look up in TABLE 8-6

  1. ADJUSTMENT FACTOR:                     Fd; Look up in TABLE 8-4
  2. WIDTH FACTOR:                                 Fw; Look up in TABLE 8-5
  3. CAPACITY:                                           SFx = Sfideal (VCRSF) (Fd) (Fw) (FHV)

2.      VCRSF                                              Look up in TABLE 8-1 using %NoPassing & Type of Terrain

  1. LEVEL OF SERVICE (L.O.S.):             Using thresholds from CAPACITY calculations at various L.O.S.

 

 

L.O.S. CALCULATION FOR MULTILANE:

 

  1. HEAVY VEHICLE FACTOR:               FHV = 1 / [1 + Pt (Et – 1)]

3.      Et (Terrain Factor)                             Look up in TABLE 7-7

  1. PEAK HOUR FACTOR:

4.      If “Rural Highway” then                        PHF = 0.85

5.      If “Suburban Multilane” then                 PHF = 0.92                       

  1. SERVICE FLOW RATE (pcphpl):          vp = V / [(NoLanes) (PHF) (FHV)]
  2. MEDIAN TYPE FACTOR:                    Fm; Look up in TABLE 7-2
  3. LANE WIDTH FACTOR:                      Flw; Look up in TABLE 7-3
  4. LATERAL CLEARANCE FACTOR:     Flc; Look up in TABLE 7-4
  5. ACCESS-POINT DENSITY ADJUST.:         Fa; Look up in TABLE 7-5
  6. FREE-FLOW SPEED:                            FFS = FFSi – (Fm + Flw + Flc + Fa)
  7. LEVEL OF SERVICE (L.O.S.):             Look up in TABLE 7-1 using vp & FFS

 

 

The following example describes the new List of Fields created for the ArcView project application to recognize roadway attributes in the MCAG model.

 

LIST OF FIELDS

 

NEW FIELDS:

 

TRAFFIC MODEL:

1.      A              

2.      B

3.      Lanes                     # of lanes per direction

4.      TSVA (Speed)       Speed

5.      V1_1 (Vol)                        Volume of traffic per direction

6.      TOTV (Aadt)         Total volume of traffic in both directions

7.                  Name               Designation of roadway names; this will need to be revised for other counties, because currently, these names are hard-coded (Interstate & State Routes) in the application.

8.      Numways (Rev)     Directionality (either 1 or 3)

9.                  Class                This item could be used to replace the “RTE” designation. The application could be revised (reprogrammed) to look at “CLASS” (Freeway, Rural Highway, or Multilane), to make it more generic, vs. the roadway names (I-5, Hwy 99, Hwy 152…). This classification may already exist in other traffic model data as some numeric values, and they would only have to be reevaluated, on the traffic model side, in a new character field.

 

The CTGLA then accepts the transportation model network as a converted shapefile, with the three identified roadway classes already pre-defined in the attribute file of the model. The ArcView program is launched normally and a series of validation screens are initiated to verify that project information from a previous run is still acceptable, or if new information will be used. This allows the user to provide additional information consistent with any new changes that were made to the transportation model, such as the addition of new network links, since the previous run. After the project is updated the application begins to perform a series of calculations associated with the identified roadway classes. At this point, the application will make a copy of the “working” data layer ( <layer>_los.shp ). This copy will then be modified, stripping out the nonessential fields and adding the new pertinent L.O.S. items. Next, the values for these new L.O.S. items will be calculated/determined using default figures. At this point the front-end L.O.S. application dialogs will activate. The opening View (Figure 1) displays the map of Merced County, and the resulting LOS for the SHS, color-coded by letter designations. In addition to this an LOS Analysis Dialog User Interface (Figure 2) appears which allows the user the opportunity to manipulate various factors and recalculate the LOS for user defined segments or for the entire network.

 

 

Level Of Service Application

 

Figure 1.  LOS Application View with User Interface

 

 

Example of Level of Service Factors used for the re-calculation options:

 

1.                  Free-flow Speed

2.                  Annual Average Daily Traffic

3.                  Percentage of Trucks

4.                  Terrain Factor

5.                  Directional Split

6.                  Peak Hourly Factor

7.                  Conditional Maximum Service Flow

8.                  Number of Lanes in Peak Direction

9.                  Width of Lanes (Feet)

10.              Width of Shoulders (Feet)

11.              Percentage of No Passing

 

 

Calculations For Level Of Service (LOS)

 

Figure 2.  LOS Dialog Interface (inset from Figure 1)

 

 

LOS Dialog:

 

User Options For FREEWAY:

 

  1. FREE-FLOW SPEED             55, 60, 65, 70 mph
  2. AADT                                      Not constrained
  3. % TRUCKS IN PEAK HOUR            Not constrained
  4. TERRAIN FACTOR               Level, rolling, or mountainous
  5. DIRECTIONAL SPLIT                       Not constrained
  6. PEAK HOUR FACTOR                     Not constrained
  7. # LANES & MSEI                  2 (Msei = 2200) or 3 (Msei = 2300) lanes per direction

 

 

User Options For RURAL 2-LANE HIGHWAY:

 

  1. FREE-FLOW SPEED             35-70 mph
  2. AADT                                      Not constrained
  3. % TRUCKS IN PEAK HOUR            Not constrained
  4. % NO PASSING                                Not constrained
  5. TERRAIN FACTOR               Level, rolling, or mountainous
  6. DIRECTIONAL SPLIT                       Not constrained
  7. PEAK HOUR FACTOR                     Not constrained
  8. WIDTH OF LANES                9-12 feet
  9. WIDTH OF SHOULDERS     0, 2, 4, 6+ feet

 

 

User Options For MULTILANE:

 

  1. MEDIAN                                 Divided or undivided
  2. REGION                                 Rural or suburban
  3. FREE-FLOW SPEED             45, 50, 55, 60 mph
  4. AADT                                      Not constrained
  5. % TRUCKS IN PEAK HOUR            Not constrained
  6. TERRAIN FACTOR               Level, rolling, or mountainous
  7. PEAK HOUR FACTOR                     Not constrained
  8. WIDTH OF LANES                10-12 feet
  9. WIDTH OF SHOULDERS     0, 2, 4, 6+ feet
  10. ACCESS POINTS                  Not constrained

 

 

The application at this point of the project maximizes the full potential of the ArcView program by allowing the user to utilize the LOS Analysis Dialog to analyze the three pre-defined SHS roadway classes, at the link, corridor, or network level. Any of the conditional factors can be changed and re-calculated, reviewed, and even displayed in a map.

 

At this point, if additional information on the impacts to the entire network is desired, based on changes made to a specific link or corridor, the shapefile must both be interfaced back to Viper and re-run with the TP+ program. Another option would be to create a new model run with new alternatives in the TP+Plus program, convert it back to a shapefile and re-calculated in the CTGLA.

 

 

CONCLUSION AND NEXT COURSE OF ACTION

 

The California Department of Transportation GIS Level OF Service Application demonstrated the benefits of an existing and available integration of two types of systems, transportation network models and GIS. The “user friendly” environment of the ArcView program allows the transportation analyst to import a transportation model with all associated network attributes and utilize the Highway Capacity Manual methodologies to review, analyze, modify, and display calculations and results with no additional post-processing activities between the three program platforms. Although an intermediate knowledge of transportation modeling, ArcView GIS, and HCM methodologies is helpful, ArcView users using this project application can immediately utilize transportation model data and begin performing HCM analysis, with minimal training in both programs. 

 

The update of the LOS methodologies to HCM 2000 is in progress, with consideration of also including the analysis of interrupted flow facilities.

 

 

ACKNOWLEDGEMENTS

 

California Department of Transportation

Division of Transportation Planning

1.      Office of Advanced System Planning

Division of Transportation System Information

1.      Office of Travel Forecasting and Analysis

1.      Office of GIS

District 10 Division of Transportation Planning

Merced County Association Governments

 

 

REFERENCES

 

Publications

Urban Planning and Development Applications of GIS

Edited by Said Easa and Yupo Chan

Copyright 2000 by the American Society of Civil Engineers

 

Highway Capacity Manual Special Report 209

1998 by the Transportation Research Board

National Research Council

 

Highway Capacity Manual

2000 by the Transportation Research Board

National Research Council

 

Viper 2.0 Manual

2000 The Urban Analysis Group / Citilabs Company

 

TP+ 2.0 Manual

2000 The Urban Analysis Group/Citilabs Company

 

Introduction to ArcView GIS –Developed for Caltrans by Esri

1992-2000 Environmental Systems Research Institute, Inc.

 

 

 

 

AUTHOR INFORMATION

 

Name: Carlos P. Yamzon

Title: Senior Transportation Planner

Organization: California Department of Transportation

Address: Caltrans District 10

1976 E. Charter Way

Stockton, CA 95205

Telephone: 209-948-3975

Fax: 209-948-7194

e-mail: carlos_yamzon@dot.ca.gov