Road System Growth
Road system growth refers to adding new roads or additional lane miles on a state highway, county road, city street or bridge.
Road system growth often occurs in response to safety or 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. (See our Land Use and Bike Walk Roll pages)
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 long-haul freight truck. Enough demand for some roads can cause them to become congested with traffic.
When that happens, one solution is to add more lane miles in strategic locations to alleviate that congestion. But that needs to be done carefully to avoid latent demand and induced demand.
Latent demand and induced demand are phenomena where adding new lanes or building new roads causes more people to use them. Drivers see the new capacity and assume their trip will be faster or better; after all, more lanes or a new road means more space for more cars, right?
At first, this assumption holds true. But eventually, too many people choose to use that new lane or road — based on the premise their trip will improve — and the new lane or road becomes congested with traffic.
We can control for latent demand and induced demand with smart planning. The key is identifying when they might occur as a result of a transportation project. The process is documented in the Oregon Department of Transportation Analysis Procedures Manual.
Oregon’s state agencies have several tools available to reduce the chances latent demand and induced demand occur in Oregon: Tolling; road diets; transportation demand management programs; and investments in biking, walking and rolling, and transit infrastructure. Sharing the road by reallocating more space for active and public transit can help smooth traffic, improve safety, and reduce emissions, as demonstrated in Oregon. While Oregon has few tolled bridges and even fewer HOV and freight/bus only lanes, these have proven effective elsewhere. 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. New technology like ramp metering and signal coordination that improve traffic reliability can be considered before expanding road capacity. (See our Land Use and Intelligent Transportation Systems pages)
Limiting road growth and addressing latent demand and induced demand are key strategies for managing the transportation system and meeting emission reduction goals.
Road system growth: emissions reduction vision
Road system growth will be kept to a minimum through 2050. 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 people in Oregon.
How Oregon is doing
Oregon’s road system growth has remained low over the last two decades. Between 2018 and 2025, total statewide lane miles increased less than 1% (counting only state, county, and city roads submitted for federal reporting). Most of that growth occurred on local roads to accommodate new homes and businesses. A number of projects address road safety or efficiency projects like turn lanes, highway ramps, and truck climbing lanes.
State and local road growth is often driven by a growing population. Between 2015 and 2025 Oregon’s total miles driven in the state increased by 5%, which grew slower than the state’s population which increased 7% in the same period. Oregonians are driving less per person (2% drop in average miles traveled per capita), limiting the need to expand our roads.
One contributing factor to the modest growth is Oregon’s transportation system is mature. We do not need many new lanes or roads to accommodate our projected slow, steady increase in population.
Another factor is new long range planning rules for local transportation system plans that require additional reviews of capacity expanding projects, which need to show that when combined with other projects will not increase vehicle miles traveled faster than population growth. These new requirements have caused some local agencies to rethink their projects that expand road capacity.
How Oregon can improve
The key will be to couple road growth with user-pays funding and policies that limit growth in demand while keeping Oregonians safe and freight moving.
Maintain current policies
ODOT and local transportation agencies can stay on track by limiting road growth to strategic expansions to match population growth, alleviate severe congestion and bottlenecks, and reduce crashes.
New roadway projects also need to follow state policy to exhaust other options before expanding capacity (see the Intelligent Transportation Systems, Congestion Pricing, and Transportation Options pages), and to prioritize reduction of severe and fatal crashes.
The Oregon Department of Transportation can help inform strategic decisions through their data tracking programs. The agency tracks statewide vehicle miles traveled, congestion, bottlenecks, and other related factors (see the State of the System website). ODOT could take additional steps to track potential impacts of roadway expansion projects like documenting induced demand evaluations and project monitoring.
With limited funding, ODOT needs to cover basic maintenance first. New road expansion will need to find new revenue sources.
A multimodal future
Reducing the amount of driving individuals need to do, especially in urban areas where other options are available, will slow — but not fully stop — the overall growth in vehicle miles travelled from a growing population. In turn, this will help limit the need for adding more roads to Oregon’s system.
Oregon has started down that path. We can reach our 2050 vision by:
Control for induced demand on road projects, according to state policy.
Follow recent land use laws that shape communities to be better and safer for people biking, walking and rolling, and riding transit.
Follow new planning requirements that ask for additional reviews of capacity expanding projects and consideration of alternatives.
Invest in demand management programs, especially during disruptions like road construction, to keep roads flowing smoothly.
Follow guidance like ODOT’s Blueprint for Urban Design to safely balance road use among users.
Couple any planned road growth with appropriate road pricing strategies. Limited funding needs to cover basic maintenance first. (See our Pricing, Funding and Markets pages)