If you’ve lived in the East Bay long enough to remember I-80 before Caltrans added lanes, you know that the congestion now is…about the same as it was before the new lanes. Only, now more cars and trucks inch along, producing more greenhouse gas emissions and deepening the climate crisis.

The failure of this particular highway widening to achieve its stated goal of relieving congestion is no surprise. Engineers have known for decades that wider roads lead to more driving — induced demand — that soon erases any gains from the additional capacity. But knowing and acting on that knowledge are two different things. New “congestion relief” projects on I-680 near Walnut Creek, US 101 along the Peninsula and Highway 37 in the North Bay will throw more money and resources into additional lanes, providing temporary congestion relief while worsening climate change and air pollution. So it’s worth taking a deeper dive into highway widening, the science behind induced demand, and effective solutions to traffic congestion.

Why doesn’t widening relieve congestion?

Induced demand is the concept that if you build more road capacity, more people will drive until congestion reaches the same levels as before you widened the roadway. UCLA postdoc Amy Lee, in a recent interview with Yale Climate Connections, said her research shows that what she calls “induced travel” brings congestion back to pre-widening levels in five to 10 years.

Several factors lead to induced demand. With less congestion initially after a highway is widened, existing drivers make more frequent trips and travel at peak hours when congestion is the worst. Additionally, people who would have traveled by other modes, such as walking, biking, or public transit, shift to driving. A wider highway could encourage developers to build more housing or businesses to locate jobs in far-flung suburbs because the commute appears short enough. And studies show that wider highways don’t shift traffic from other roads; they lead to more driving overall.

So induced demand leads to more driving and more vehicle miles traveled (VMT), which slowly ratchets congestion back up, at which point the solution is to…add even more lanes?

Highway widening to reduce congestion seems logical on its face. If 1,000 cars an hour want to move through a section of roadway that can only handle 500 cars per hour, the extra traffic will cause backups that slow everyone down. If you widen the highway so it has a capacity of 1,000 cars an hour, traffic flows freely, and the problem is solved.

Then drivers see traffic flowing freely, and some who previously avoided the congested section decide to drive on it. Before long, the traffic exceeds the capacity of the highway. Versions of this scenario have been repeated multiple times throughout the United States since the advent of driving.

We can push our bloated highways to their maximum width, funneling more people into single-occupant vehicles and worsening the climate catastrophe California has committed to ameliorate. Or we can accept that highway widening isn’t a truly viable solution for traffic congestion. Instead of waiting until we’ve paved every possible square foot of land, we could look in a different direction now.

Solving for climate and congestion

The solution to our congested roadways is twofold: internalize the true cost of driving and provide better alternatives. The all-lane tolling and road user charge options currently being studied by the Metropolitan Transportation Commission (MTC) and piloted at the California Transportation Commission would make driving more expensive in a way that drivers will feel directly, as opposed to the costs of gas, insurance, maintenance, and parking, which people often discount when they’re calculating the economics of their commutes. Any revenue generated from pricing could be reinvested in driving alternatives and discount programs that lessen the burden for lower-income people who still need to drive.

Offering viable alternatives to driving also relieves congestion. Riding a BART train through the tunnel under the bay is faster than driving across the bridge, and passengers don’t have to pay for parking at their destinations. For transit to be an appealing option, however, it needs to be frequent and reliable. When trains or buses come every few minutes, people know they can show up at the station or stop and hop on. If there are long gaps between trips, taking the bus could add significant travel time, making driving more appealing. People — especially vulnerable passengers such as women, people of color, and seniors — also need to feel safe taking transit. Reliable, frequent buses and trains contribute to safety.

Instead of planning for new highway widening projects that take years to design and build, cost millions of dollars, and don’t solve congestion, California should be focusing on providing better transit, walking, and biking options for all.

A longer-term solution that’s equally critical is to reverse the sprawl that highway widening facilitates and build affordable, dense infill housing near transit, jobs, schools, and community amenities. Rather than forcing low-income residents farther and farther to the edges of the Bay Area, infill development reduces commute times and saves money. BART is moving forward with transit-oriented developments on top of several stations in the East Bay. The regional housing bond measure Transform championed in 2024 would allow many shovel-ready affordable housing projects to break ground; it was pulled from the November ballot, but we hope it comes to voters soon. 

Building more compact neighborhoods and cities is a long-term project but a necessary one. Housing policy can have as big an impact on climate as transportation. Combined with fees or tolls to reduce VMT and enhanced public transit, these solutions will create healthier, more appealing neighborhoods instead of inhospitable cement wastelands of ever-widening highways.