For decades, many transportation and land use decisions were shaped by how easily cars could move through a place. In California, and across the country, roadway planning often considered “level of service,” a measure of how well a roadway moves cars and how congested it is for drivers. In practice, this often-encouraged more sparse development to keep congestion was lower, contributing to more roadbuilding, longer commutes, and expanded sprawl.

In 2013, California began moving away from that approach and toward a focus on Vehicle Miles Traveled, or VMT which measures how much people drive, making it possible to evaluate whether development decisions reduce traffic, support transit-oriented growth, and help lower greenhouse gas emissions.

This shift created an important opportunity. Instead of simply asking whether cars can move quickly, California could ask better questions: How far are people driving? Are communities being designed in ways that reduce transportation costs? Can land use decisions support both climate goals and household affordability?

But there was also a challenge.

As transit-oriented development became a stronger priority, housing near transit became increasingly valuable. In some communities, this increased pressure on housing markets and raised concerns that lower-income residents could be priced out of the very places where transportation costs are lower and opportunity is easier to reach.

The California Air Resource Board (CARB) recognized the problem but needed a better way to understand the scale of the issue and where it was happening. That is where CNT’s tools and expertise came in.

How CNT’s Tool Is Creating Change

CNT worked with the University of California Davis for CARB to develop a specialized version of the H+T Index that incorporates California’s VMT metrics and reflects driving patterns across the state.

The modified index will help CARB and its partners better understand how transportation behavior, household costs, and emissions are connected. It can help identify places where residents face high combined housing and transportation burdens, as well as places where investments in affordable housing near transit could make the greatest difference.

The goal is not simply to produce another dataset. The goal is to make the impact of policy choices visible, by allowing CARB to put specific policy scenarios into the model to understand their effect on VMT and overall transportation and housing costs.

With this information, decision-makers can more clearly see where transportation and housing policy are working together, where they are creating unintended burdens, and where targeted action could improve outcomes for vulnerable communities.

For example, the index can help answer questions like:

• If California eliminated the gas tax but then taxed miles driven, and put the additional revenue into transit improvements, how would this lower VMT and household transportation costs?
• Where are households spending too much on transportation because they live far from jobs, transit, or daily needs?
• Where could affordable housing near transit reduce household costs and support climate goals?
• Where might transit-oriented development increase displacement pressure unless affordability protections are included?

These are the kinds of questions that turn data into action. They help public agencies and community partners move from broad concern to targeted solutions.

The History and Purpose of the H+T Index

CNT’s H+T Index was built in 2006 around a simple but powerful idea: affordability is about more than the cost of housing.

Traditional affordability measures often say that housing is affordable if it costs no more than 30 percent of household income. But that measure leaves out a big component, transportation. Even though these expenses are second only to housing in the average household budget, they are directly impacted by where the housing is located.

CNT’s H+T Index fills that knowledge gap in a format that is adaptable to the question being asked. It shows the combined cost of housing and transportation, giving users a more accurate picture of what it actually costs to live in a neighborhood.

The data has consistently shown that location matters. In denser, amenity-rich communities, residents often have more options for travel. They may be able to take transit, walk, bike, or drive shorter distances to reach work, school, groceries, health care, and other daily needs. Those choices lead to reduced transportation costs and give households more flexibility in their lives.

By contrast, housing located far from transit and essential services may appear affordable at first, but the savings can disappear when residents must rely heavily on cars. Car payments, insurance, maintenance, gas, parking, and longer commutes all add to the real cost of living.

This is why the H+T Index remains an important tool and one that continues to adapt to the needs of today. It helps communities understand that affordable housing cannot be separated from transportation access, land use, environmental quality, and economic opportunity.

From Information to Impact

The H+T Index has long supported planning, research, advocacy, and policy conversations across the country. But its value is not limited to the numbers it produces.

Its real impact comes from how people use it and how it can be adapted to speak to local issues that communities face today.

Community advocates can use the tool to show how transportation costs affect household stability. Planners can use it to understand where transit investments may reduce financial burdens. Policymakers can use it to evaluate how housing, transportation, and climate decisions interact. Funders and partners can use it to see where investments may create the greatest benefit for residents.

In California, CNT’s work with the University of California Davis and CARB shows how the H+T Index can be adapted to meet urgent policy needs. By incorporating VMT and state-specific driving patterns, the tool can help support more precise analysis of housing affordability, transportation patterns, and emissions.

That matters because climate policy and affordability policy are often treated as separate conversations. In reality, they are closely linked. When people can live near transit, jobs, and daily needs, they can often spend less, drive less, and access more opportunities. But without intentional affordability protections, the benefits of transit-oriented development may not reach the people who need them most.

CNT’s work helps make those connections clear.

Where the Index Goes Next

CNT continues to track how the H+T Index is used, cited, and applied in communities across the country. Since 2023, we have seen growing interest in how the tool can support local planning conversations, municipal decision-making, policy analysis, and community advocacy.

Looking ahead, CNT will continue adapting the tool to respond to changing conditions and emerging needs. That includes exploring how it can better support conversations around climate policy, transportation equity, affordable housing, and household cost burdens.

The specialized version developed for CARB offers one example of what is possible. It shows how CNT’s tools can be adapted for specific policy environments while staying rooted in the same core purpose: helping people see the true cost of place.

For institutional funders, this is the kind of impact their investment makes possible. Support for CNT and the Data Trust and Knowledge Lab helps ensure that communities, agencies, and advocates have trustworthy, accessible knowledge that turn complex issues into clear choices. It helps make hidden burdens visible. It helps connect data to policy. And it helps build a future where affordability is measured not just by the cost of a home, but by whether people can truly thrive there.