As the population of Washington continues to grow by more than half a million people each decade, city planners are constantly looking at new and more effective ways to reduce the negative impact of urban sprawl on the state’s environmentally significant areas.

One of the most successful methods of doing this has been through the implementation of TDR programs.

In the parlance of town planners, developers and conservationists, TDR stands for Transfer of Development Rights.

What it means to the rest of us is a powerful, incentive based tool to keep farms and forests untouched, and encourage developers to concentrate their development where the local government decides it is appropriate.

This is how it works:

Say you have a piece of farmland, or an environmentally sensitive wetland area.

Though the owners of that land have every right to develop it, the city’s planners hope that they don’t, due to the environmental and social consequences.

So they suggest a TDR program for that parcel. That parcel is known as the “sending” site.

Now what happens is developers, who, let’s say, are putting together an apartment complex or a neighborhood somewhere else in the city area, can offer to buy TDR credit from the owner of the farm or wetland.

The purchase price is seen as being compensation to the owner of the farm or wetland for giving up their right to develop.

What the developer gets is special allowances from the city to exceed height or density restrictions at their apartment complex or neighborhood. That is the “receiving” site.

Essentially what TDR’s do is use the economic engine of growth to conserve lands with public benefit.

Though the TDR system is growing in popularity with local and state governments all across America, it is not a new idea.

The first known TDR initiative was in 1968, in New York.

The city used TDR credits to protect landmark buildings such as Grand Central Station, by transferring development rights from this site to adjacent properties.

Forty years later, the City of Issaquah has used a TDR program to protect land around Issaquah Creek, a significant spawning stream for threatened chinook salmon.

A joint Issaquah/King County TDR agreement allows private landowners in the Issaquah Creek basin – the area just outside the southern limits of the city – to sell or transfer their development rights to developers inside the city for increased density or height allowances.

As a result of the TDR, 10 acres of land in the basin were preserved.

Last month the city was named declared a leader in open space conservation by King County, and received a top environmental honor – the Green Globe Award – during the county’s Earth Day celebrations.

“Our environment does not have boundaries,” said Issaquah Mayor Ava Frisinger. “Through this partnership with King County, we can help protect important sensitive areas in our region – which also benefits Issaquah – as well as implement several key objectives of smart growth.”

In 2007, the City and King County signed a partnership agreement that focused development in the City’s existing urban areas, and away from high priority open space lands and salmon habitat located in rural King County.

According to a study of TDR programs by the Cascade Land Conservancy last year, in addition to height and density incentives, purchase of TDR credits could be offered as an alternative to providing required environmental mitigation.

The study’s authors used the example of instances when surface water impacts can be mitigated by the preservation of nearby farmland.

Flexible initiatives like this are seen as more holistic solutions to some classic development problems, such as the flow-on effect of development through watersheds.

The Cascade study says that as the TDR is a market-based mechanism, it relies on market activity, and “as such, can succeed only if there is demand for development. If developers are not interested in building to the higher densities established for receiving areas, there will be no marketplace for TDRs.”

The study goes on to cite the Issaquah Creek TDR as an example of the program’s successes.

A TDR program was enacted in Redmond in 1995, which allowed developers additional square footage, or a reduction in parking or open space requirements, for protection of agricultural lands and critical areas in the Northern Sammamish Valley.

The city has conducted a number of TDR programs since.

According to City of Issaquah Senior Planner Debi Kirac, the first TDR to be adopted in this area was when a parcel of land to the east of the Issaquah Highlands development, known as Mitchell Hill, was protected by offering developers concessions in the fledging highlands project.

“It is still a new tool, and there aren’t too many medium sized cities using it yet,” she said. “But it is one that we hope to see used more in the future.”

Kirac said that city planners had identified a number of “sending” sites in the city, that is, ecologically sensitive areas they hoped to see preserved.

At present, all “Priority 1” sending sites are along the Issaquah Creek. There are a number of “Priority 2” sending sites along Tibbetts Creek.

Kirac said that developers, “receiving” sites, once registered as such, could either negotiate a the purchase of credits with the sending site directly, or conduct a transaction with the City of Issaquah.

The city itself has purchased a number of credits from sending sites.

The City of Sammamish is just beginning to explore how TDR programs might shape development on the plateau, in particular with the offering of concessions to developers in the new town center.

On Thursday night, their Planning Commission met to discuss just that, during a review of incentive options for residential and commercial development that could help them achieve their goals which include, amongst other things, 400 affordable housing units in the town center, and a number of specific amenities and sustainable elements.

The City of Sammamish has also identified a number of possible sending sites, along Ebright Creek in the Thompson Basin, and parcels in the Patterson Creek Basin in unincorporated King County just past the eastern boundary of the city.

City of Sammamish Director of Community Development Kamuron Gurol said this week that although TDR’s had the potential to play an important role in the development of Sammamish, it was a complex tool that needed to be used correctly.

“For one thing, creating a marketplace for TDRs is not an easy or straightforward thing to do,” he said. “And it is not something that governments do very often. The key is to make sure that marketplace is fair and helps to accomplish the goals of the public.”

Gurol said that in town center discussions to date, developers had expressed an interest in TDR opportunities.

“But they want to know what the rules are,” he said. “They want to know how much will this cost, and will I make more money by doing this?” It’s got to be sweet enough for the developers to get involved.”