California Department of Transportation GIS/Level of Service Application
Carlos P. Yamzon
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.
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.
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
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
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
L.O.S. CALCULATION FOR FREEWAY:
1. Et (Terrain Factor) Look up in TABLE 3-3
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. If NoLanes = 2 (Per Direction) then Msei = 2200
2. If NoLanes = 3 (Per Direction) then Msei = 2300
1. Et (Terrain Factor) Look up in TABLE 8-6
2. VCRSF Look up in TABLE 8-1 using %NoPassing & Type of Terrain
L.O.S. CALCULATION FOR MULTILANE:
3. Et (Terrain Factor) Look up in TABLE 7-7
4. If “Rural Highway” then PHF = 0.85
5. If “Suburban Multilane” then PHF = 0.92
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
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)
Class This item could be used to
replace the “RTE” designation. The application could be revised (reprogrammed)
to look at “CLASS” (Freeway,
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
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
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
Figure 2. LOS Dialog Interface (inset from Figure 1)
User Options For FREEWAY:
User Options For RURAL 2-LANE HIGHWAY:
User Options For MULTILANE:
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.
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.
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
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.
Name: Carlos P. Yamzon
Title: Senior Transportation Planner
Organization: California Department of Transportation
Address: Caltrans District 10