Road System Growth
Road system growth refers to adding new roadways or additional lane miles on a state highway, county road, city street or bridge.
Road system growth often occurs in response to demand on the transportation system. Two common triggers to more demand are population and economic growth; as more people and businesses need to drive on our roads, demand goes up.
Road system growth to meet that new demand is not inevitable. Oregon’s land use laws and investments in infrastructure for biking, walking and rolling can divert some of that demand to non-driving modes.
However, some people will still need to drive to get where they need to go, and many goods still need to move through the state by freight truck. Enough demand for some roads can cause them to become congested with traffic. Adding more lane miles in some strategic locations can help alleviate that congestion, but that needs to be done carefully to avoid phenomena called latent demand and induced demand.
Latent demand and induced demand are complex topics but in short: if drivers think a new road or lane will make their trip faster or better, they will choose to drive there over another route or another mode.
Drivers may experience faster or better trips on the new road in the short term, but eventually, enough people have the same thought, which causes more people to drive on that road than before. Thus, the new road becomes congested again.
The key is identifying when latent demand or induced demand might occur as a result of a transportation project. ODOT does this through analysis, and the process is documented in the Oregon Department of Transportation Analysis Procedures Manual.
Oregon’s state agencies have several tools available to meet latent demand and induced demand head on and reduce the chances they occur in Oregon: congestion pricing; road diets; transportation demand management programs; and funding for biking, walking and rolling. Each project is different, and tools are used where they’ll work best.
Supportive land use practices can also help to limit unplanned increases in demand for driving.
Limiting road growth and addressing latent demand and induced demand are key strategies for managing the transportation system and meeting emission reduction goals.
Note: sometimes, strategic road growth is needed to address safety issues, not congestion ones.
Road system growth: emissions reduction vision
Road system growth will be kept to a minimum through 2050 and measured as road miles per capita. Priority will be given to safety issues, and critical bottlenecks on interstates and freight routes.
State and local transportation authorities will use tools like pricing and demand management to counteract latent demand and induced demand from new added lanes.
Increased multimodal investments and travel demand programs will help incentivize and improve non-driving options for Oregonians.
How Oregon is doing
Total statewide lane miles increased 9.6% between 2000 and 2021. Most of those changes occurred on local and county roads to accommodate new housing and businesses.
State and local road growth can be attributed to Oregon’s growing population: between 2000 and 2021, Oregon’s population grew 25%. That increase coincided with a growth in the total miles driven by Oregonians over that same period. In contrast, the average miles traveled per capita has declined since 2000.
The takeaway: while individuals may be taking fewer and shorter trips by car, Oregon’s growing population is outpacing that reduction, leading to more driving overall. (See ODOT’s 2022 Statewide Congestion Review for a more in-depth discussion on this subject.)
How Oregon can improve
State and local agencies are on track in this area and must maintain their minimal road growth policies going forward. The key will be to couple road growth with policies that limit growth in demand while keeping freight moving.