UW researchers are using a computer program to simulate the effects of transportation projects on long-term land use and future travel patterns in the Puget Sound area.

Researchers began developing the open-source model, UrbanSim, in 1995, and have already used the program to help planning agencies in Houston, Salt Lake City, Detroit, and Honolulu with transportation and land-use policies.

The program helps link road plans to city growth.

"For example, we analyze the effect of major highway projects like the 520 bridge or the viaduct and look at how those projects influence patterns of urban development and real estate prices," said Paul Waddell, a professor of public affairs and the director of the Center for Urban Simulation and Policy Analysis.

Planning agencies have traditionally overlooked the role of new transportation on people's travel patterns and new real estate development, Waddell said.

Looking at the history of Seattle's development, it's clear that new transportation infrastructure can have a dramatic impact on where people live and how they travel, said Alan Borning, a computer science and engineering professor and the co-director of the Center of Urban Simulation and Policy Analysis

"If you look historically at the U-District, it was really a streetcar suburb," Borning said. "Before the streetcar, it was pretty inaccessible. Similarly, Lynwood was a child of the inter-urban line."

Predicting how a new subway or highway will affect development can be difficult because so many different variables interact in complicated ways, Borning said.

"In some regions it's just hard enough that planning agencies say 'we'll ignore it,'" he said. "They just assume people will live in exactly the same places, which is clearly not true, but trying to agree on what's valid is a difficult problem."

By analyzing new travel patterns, UrbanSim can also help policymakers understand land use and transportation's environmental impact.

"In Washington state, most of the greenhouse gas emissions are from transportation, so if we want to cut greenhouse gas emissions, we have to look at transportation," Borning said. "Light rail tends to encourage more compact development along the line. With freeways, it's quite controversial. One argument is that if cars are stuck on the freeway in traffic then they will move faster and emit less pollutants, but another argument is that the number of cars will not stay constant — they'll increase."

This induced demand helps explain why new highway projects are congested as soon as or soon after they've opened.

"Once we get a congested highway — for instance, the I-5 corridor downtown — it's extremely difficult to get anything to change, except by reducing demand through that corridor," Waddell said.

Building "fixed guideway" systems like light rail also boosts demand for light-rail travel, but the large increase in riders can often be offset with more frequent service, he said.

The Center for Urban Simulation and Policy Analysis, in collaboration with the Puget Sound Regional Council, is currently using UrbanSim to model the Puget Sound region's expansion and travel patterns over the next 30 years, Borning said. The results aren't in yet, but they may provide key information in one of Seattle's most hotly contested issues: the viaduct replacement.

"It is intriguing that the second best option for both the legislature and the mayor appears to be the surface transit option," Waddell said. "I think that option warrants additional exploration. I'd like to see if the fears of causing gridlock are completely warranted, or if design may mitigate those effects by providing good transit options, using other arterials through downtown and pricing to reduce demand."

Reach reporter Tia Ghose at news@thedaily.washington.edu.