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When it comes to improving freeway traffic flow, sometimes a bigger road really isn’t a better one.

An investigation by the Oregon Transportation Research and Education Consortium found that projects designed to expand freeway capacity can actually make congestion problems worse – by creating more traffic instead of reducing delays.

Lei Zhang, an assistant professor of civil and environmental engineering at the University of Maryland, recently he did for the group over the past several years. In his research, he modeled several scenarios and development plans for freeway construction in a generic city.

He started the work for OTREC when he was an assistant professor at Oregon State University.

The models looked at congestion, societal impacts of projects, new building development, evolution of road trips and land-use responses to freeway development, among other things. Zhang used it to compare what would happen if transportation planners decided to stop building new freeway capacity versus continuing with the status quo.

“In simple terms what we found is if you build more you just get more people using the freeway,” Zhang said. “In the short term it helps, but then you get more development, more residential and more people using that and you get new bottlenecks.”

In the model, scenarios where freeway money was diverted to other projects – such as mass transit, improving arterial neighborhood streets and bumping up investment for bridge maintenance – worked more effectively than those that simply built new capacity, he said.

“In the generic model we found that the no-new-freeway policy was more efficient, and we didn’t expect that,” Zhang said, adding that efficiency equates to faster travel speeds, fewer delays and less congestion. “The results on the test city show that not investing in freeway capacity is good for both mobility and sustainability.”

In general, over the first 20 years of the no-new-freeway plan, the study found a 15 percent to 20 percent reduction in travel delays from congestion.

“We were surprised by several of the findings,” Zhang said.

On the other hand, continuing to build out capacity as a means of dealing with bottlenecks turned into a sort of money pit, with project costs continuing to rise until they became too expensive to fund, he said of the model.

“It gets into a vicious cycle,” Zhang said.

Without new freeways, development in the generic city spread through several areas and the travel patterns became more balanced.

“You end up with more use of side streets,” Zhang said. “With corridors, they always end up limiting growth – the more money you put in, the more expensive it gets and you have diminishing returns.”

The model also investigated the impact of private-sector versus public-sector road development.

“We found that private-sector investments improved things, but only marginally,” Zhang said. “You have to regulate them to make sure it works the right way, but overall it can be a good thing.”

Justin Carinci, a spokesman for OTREC, said the research could be useful to planners in Oregon as they decide how to distribute limited highway funds.

“In the Oregon Legislature you have to look at congestion pricing; you have to look at tolling and find what’s most efficient for the Portland-metro region,” Carinci said. “The best private-sector scenarios regulated companies to 18 percent return on investment, which seems to be a realistic idea.”

The study was paid for via matching $44,000 grants – one from OTREC and one from OSU. Now that he’s in Maryland, Zhang intends to continue his work by tweaking the model to look at scenarios in real cities, including Portland, he said.

“Portland is widely acclaimed as one of the better planned cities in the United States, and I think it would be fascinating to examine,” Zhang said.

OTREC and Oregon planners likely will continue to follow Zhang’s work with interest, Carinci added.

“Even in the midst of a recession here, nobody has stopped looking 10 or 20 years out at the growth in the Portland area,” Carinci said. “We’re looking at more people (and) more trips, and we’re very interested in figuring out how to accommodate that.”