Oregon Department of Transportation Impacts Assessment Example

The Oregon Department of Transportation (ODOT) has established a number of work zone traffic analysis and impacts assessment practices. This example describes two activities undertaken by ODOT related to work zone traffic analysis and impacts assessment.

Highway Mobility Operations Manual

The ODOT Highway Mobility Operations Manual (PDF 2.24MB) contains case studies illustrating how ODOT has assessed and managed impacts during projects that are part of the 10-year, $3 billion Oregon Transportation Investment Act (OTIA). These case studies are at the end of each chapter in the Manual. An example of a case study is as follows:

The Mill Creek Bridge Project, along the Warm Springs Highway (US 26) in Wasco County, involved special design considerations to reduce impacts to mobility and freight traffic. For this project, ODOT had a bridge deck failure on a historic steel truss structure, which also happened to be one of the highest bridges in Oregon. The project was located on the Warm Springs Indian Reservation and was surrounded by sensitive archaeological sites, cultural sites, and endangered species. Also, this particular route is a primary freight route that carries around 5,000 vehicles per day, 15 percent of which are trucks.

Initially, three options were considered to minimize impacts:

Close the road and detour all traffic until the bridge is completed;
Build a single-lane detour bridge and alternate traffic along it; or
Re-align the highway and build a parallel structure.

These three options, however, were not viable. The roadway also could not be closed during construction because there were no suitable detour routes available and the impacts to the freight industry and the traveling public would be high (approximately $265,000 - $316,000 per day). ODOT could not utilize a single lane detour bridge due to adverse roadway geometry and safety concerns with traffic queues backing up into sharp curves. ODOT could not re-align the highway due to the excessive cost and environmental impacts. So the Project Team began seeking alternative construction methods.

In meeting with the ODOT Motor Carrier Transportation Division (MCTD) Freight Mobility Coordinator and representatives from the freight industry, the Project Team identified alternative construction materials and methods successfully used in other States. Based on this input, the Project Team decided upon a new process (exodermic deck replacement) used in New York and Illinois that required only short term closures. This exodermic deck replacement process enabled ODOT to replace small sections of the bridge with precast modular joint panels which fit together like a jigsaw puzzle. The roadway was closed for four days each week starting on Sunday night, sections of the deck were cut out, the missing sections were replaced with new precast sections, and the route was reopened to traffic each Friday morning without any restrictions. The contractor worked 24 hours a day during the closures. The entire deck was replaced in four weeks.

ODOT worked with the MCTD Freight Mobility Coordinator and freight stakeholders to help determine when the route should be opened and closed and so truckers could plan their trips. Since the closures occurred on a set schedule, fewer vehicles were required to use the extensive detours. With the exodermic deck replacement process, the project did not have impacts on the sensitive cultural, archaeological, or environmental sites adjacent to the bridge. By using this unusual method, and by closely coordinating the closures with the traffic flows, the deck was successfully replaced with minimal impacts to traffic and freight mobility and greater safety to both the contractor and the traveling public.

Work Zone Traffic Analysis Methodology

As a result of the large amount of construction work occurring from OTIA, ODOT developed a new methodology for estimating and managing project and corridor work zone delays. ODOT's work zone traffic analysis methodology is designed to predict the hours of the day during which lanes or shoulders within work zones can be safely closed, and the approximate queue length that would develop during such closures. To assist with the analysis, ODOT has developed a password-protected online analysis tool. The tool replaces an earlier spreadsheet tool and has more capabilities and significantly reduces the time needed for analysis. The new tool has a GIS interface and an interface to a traffic planning database, which enables ODOT engineers to access and import key data more easily. This methodology is augmented by using CORSIM and regression analysis to develop volume vs. delay curves, which are used to predict lane closure windows, expected queuing, and delays during any hour of any month of the statewide construction program. Additional components of the analysis also allow for assessments of other peak periods, such as holidays, and the potential for or the extent of the impacts that a work zone may cause on traffic flow.

Two presentations describe ODOT's work zone traffic analysis methodology and tool:

Presentation by Irene Toews and Jeremy Jackson, November/December 2008
Presentation by Smith Siromaskul (PDF 7.5MB) at the 2008 North American Travel Monitoring Exposition and Conference (NATMEC)

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