Interstate 5 Origin & Destination Study

Purpose of the Study

The purpose of this study is to identify existing and future needs; develop a range of alternatives (near-term to long-term) and outline the overall strategy needed to provide an efficient and functional transportation connection between the I-5 and US 101 corridors. The selected alternatives will accommodate regional growth while maintaining safe and acceptable levels of mobility.

The objectives of this study include:
  • Improve traffic mobility at the Interstate 5 / U.S. Highway 101 Interchange during AM and PM peak period
  • Increase traffic safety at the Interstate 5 / U.S. Highway 101 interchange
  • Improve the regional connectivity between the Interstate 5 and U.S. Highway 101 corridors
Origin & Destination Study

An Origin and Destination Study answers questions about the major flows of traffic through an area or along a corridor. The study looks at where vehicles are coming from, where they are going, why people are traveling, when the trips occur, and what kinds of vehicles are traveling.
A city worker monitoring traffic flow from an overpass
Study Focus Area

For this study, the focus is on trips into, out of, through, and within the urban core of Thurston County, specifically on Interstate 5 between the Nisqually River and 93rd Avenue, and on U.S. Highway 101 between Mud Bay and Interstate 5.
A machine reads traffic patterns from a city overpass
How We Gather Information

The study involved many parts. First, we gathered information about where and how many vehicles enter and leave the study area during the morning and evening rush hours. Then, we sent a survey to some of the motorists and park-and-ride users about why and how they traveled that day.
Vehicle Movement

We used several tools to look at flows of vehicles on I-5 and US 101 coming into the Lacey / Olympia / Tumwater urban area, leaving it, and using the freeway to travel among the cities.

At the edges of the study area, cameras captured the number and types of vehicles traveling on the freeway. The cameras also identified the license plates of the vehicles and determined how many and what kind of vehicles passed through the urban area, entered the area and stayed, and left the area. We used a variety of traffic counters (in pavement, tube and radar) to gather information on how many and what kinds of vehicles get on and off the freeway at different interchanges.

Combined, these sources of information provide a fairly comprehensive picture of the volume and flow of traffic using I-5 in northern Thurston County. We collected this information during the morning and evening rush hours during the week of October 25, 2010.
Traveler Surveys

Some motorists were then contacted for a short follow-up survey to ask a few questions about how and why they use I-5.  For example, we asked why they were traveling on the freeway – going to work, to school, or shopping.  The respondents were given the option to complete the paper survey or fill it online.
A flyer is placed under the windshield wiper of a car
We have completed analyzing the survey data. The results will be supporting various ongoing projects and will be integral to the local, regional and state transportation planning processes.

We also plan to incorporate the results from the survey into the regional transportation model for supporting high capacity transportation analysis.

A summary and highlights from our data mining and Origin Destination traffic flow maps is posted below. Please stay tuned to this section for a full project report.


TRPC is concerned about the privacy of travelers and survey respondents and will take appropriate steps to protect the information we gather. The survey responses are anonymous and we cannot trace those back to any particular respondent. Unless you choose to add your name to our mailing list for future studies or other transportation projects, we will delete the information after the study is complete.