Five Road Widening Myths That Are Delaying Climate Action

I-5 is wide concrete chasm between Wallingford and the U District, as seen from 45th St bridge. (Photo by author)

These convenient excuses help your transportation department justify widening and adding highways–but they’re dead wrong.

We put our environmental values right into our name in the Evergreen State. But one place we don’t put them is into our transportation system – our state’s number one source of climate emissions. Even headed into third term of a governor who has cultivated a climate leader brand, our state’s emissions stubbornly keep climbing.

Over and over again, we open giant highway megaprojects like the SR-99 tunnel–or the decade spent on the almost not quite there Puget Sound Gateway–and Governor Jay Inslee and other Democratic leaders cut the ribbon and boast of its wonders. How do we square our highway widening obsession with our aspirations of climate leadership? We probably can’t, but maybe we have rationalized each step towards climate denialism for so long that we have started to believe our own lies? Those lies have gotten very complicated and yet routine and official-sounding.

Transportation agencies seeking to widen roads increasingly point to climate impact as a benefit rather than a drawback. If you have pushed back against a project on the basis that catering to single occupancy vehicles is driving carbon emissions–particularly in Seattle with our access to generally clean choices for electricity–you have probably heard a few of the following myths about road widening and how it is good for the climate and environment.

Myth 1: Car idling is bad for the environment so wider roads with free-flowing traffic is good for the environment.

Highway departments frequently claim congested roads and a lack of free flowing traffic leads to cars idling (cars stopped in traffic with the engine on) and thus more carbon emissions and pollution. Idling certainly does emit carbon (and other pollution) to little benefit, however it isn’t a good reason to widen roads or reduce time and opportunity to cross roads on foot at the dreaded “free flowing” intersection. The Department of Energy estimates that 2% of the emissions of a car come from idling as a nationwide average. This means that if Seattle were to eliminate all idling by making traffic free flowing, just a 2% increase in driving due to these newly unjammed streets would equal the CO2 emissions saved from idling.

In brief, induced demand – lower congestion leads to more people driving further (covered here, here, here, and here) – is likely to crush any benefits of reduced idling by increasing the number of miles driven by cars – and likely lead to the return of congestion and idling, now with more cars. While these road width machinations are bound to fail, newer cars already automatically shut off engines to avoid idling and electric cars emit nothing while waiting in traffic. This myth is also well debunked here by City Observatory.

Myth 2: Relieving congestion allows buses to travel faster–it is basically an investment in public transit which is good for the climate.

If you’ve ever asked the Seattle Department of Transportation (SDOT) to remove a lane of general purpose traffic for a bike lane or wider sidewalk you have probably heard this one: “what about the buses?!” On one hand they are right, frequent rapid transit requires decongested travel lanes and leads to more people riding buses instead of driving cars which reduces CO2 emissions. Great! However, adding general purpose lanes where buses, freight, and personal vehicles mix doesn’t solve the problem. Similarly, repurposing general purpose lanes does not cause the problem.

Though widening lanes may provide momentary relief of congestion and help buses move through the city, these benefits are short-lived due to induced demand–a crucial concept to understanding why we can’t widen our way out of congestion, which is why we keep harping on it. Personal cars come back to impede each other and the buses. Rather than widening roads, dedicated space should be set aside for buses and their efficient use of space and low carbon emission per person transportation.

Councilmember Mike O’Brien helped beat back WSDOT’s effort at road widening in Montlake–for now anyway. (WSDOT)

A textbook example of this mythical rationale can be seen in the lurking project to expand the Montlake Bridge. At four lanes wide on the current bridge, transportation and the environment would be better off making two of those lanes transit only instead of expanding the Montlake bridge to be four (wider) general purpose lanes and some window dressing.

Myth 3: More people moving to the city means more motorists needing to get around–hurry, widen the roads!

The idea that a growing population requires adding highway space sounds true, like commonsense even. But reality can be counterintuitive. Seattle is growing rapidly but traffic volumes are basically flat. Local traffic engineers ignore this fact and cleave to their unofficial professional oath to always predict ever-increasing traffic and plan ever-expanding roads. The recent Ballard Bridge study was an example of this. Despite Ballard having an exploding population and mostly static traffic counts, engineers keep predicting traffic armageddon. Widening road out of old habit and traffic engineer superstition is a poor excuse and a terrible vision for the future. A growing population does need more transportation, but it has to be space efficient and have a low environmental impact, such as public transportation, walking, and biking.

Myth 4: Once all cars are electric, road widening won’t be a climate issue anymore.

Electric cars aren’t coming fast enough, and in cities we have cheaper and better alternatives ready (or nearly ready) to go. In addition, electric cars still consume large amounts of resources (energy, batteries), wear out our public roads, and cause additional environmental damage (particulates from tires and brakes, which kill salmon). Though electric cars will reduce climate emissions of our personal vehicles, that benefit does not justify their priority in cities where there are alternative modes of transportation that are safer and leave more of our public space for the joy of people.

Graphic shows how many people fit in the same streets with cars, taxis, buses, bikes and on foot. Buses, bikes, and walking and rolling fit way more people. (Geekwire)
Cars inevitably consume more street space than transit. (Geekwire)

The research suggests electric cars emit half the carbon of their conventional combustion equivalent over their lifecycle, but other forms of pollution remain in similar quantities, such as the tire and brake particles linked to salmon kill offs. Electric vehicles do not solve the issues of geometry or safety. Electric cars still take a large amount of resources to create and are expensive beyond the means for many people. The adoption rate of electric cars (and possible plateaus) are not good enough for our climate goals. Changing to electric cars may be the best option for some, but for urban transportation there are many better options.

Myth 5: It’s a chicken or the egg dilemma, we can’t give up the car while everything is so car dependent.

In some ways this is true; we have to be careful and work hard not to abandon people whose only means of accessing the benefits of Seattle are by car. But investing in highway widening crowds out investments in transit, walking, and biking and delays the transition. While some people will claim their city’s transit and walkability must be as good as London’s or Tokyo’s before they can turn away from cars. The perfect can be the enemy of the good, and Seattle’s transit is pretty good. By 2019, 70% of Seattle’s population lived within a 10 minute walk of frequent transit. We’re already a national leader in forming car-free households.

Households within a 10-minute walk of transit service with 10-minute or better frequency. By 2019, this reached 70%. (City of Seattle)

Examples from aboard show that car-dependent cities had to take the leap and once they did amazing transformations were possible. Copenhagen, Amsterdam, Paris, Madrid, Barcelona, and so on used to be largely overrun with cars, but they invested in biking infrastructure and prioritized transit and became synonymous with walkability, bikeability, transit excellence, and climate leadership. This can be our path too, but we have to choose it. We can’t wait for it to magically manifest.

We hope you loved this article. If so, please consider subscribing or donating. The Urbanist is a 501(c)(4) nonprofit that depends on donations from readers like you.

Doug Trumm is The Urbanist's Executive Director. An Urbanist writer since 2015, he dreams of pedestrianizing streets, blanketing the city in bus lanes, and unleashing a mass timber building spree to end the affordable housing shortage and avert our coming climate catastrophe. He graduated from the Evans School of Public Policy and Governance at the University of Washington. He lives in East Fremont and loves to explore the city on his bike.

Gregory Quetin is a climate scientist and aerospace engineer with a PhD and bachelor's degree from the University of Washington. He advocates for a city full of housing, commerce, industry, and recreation as ways to increase resilience to climate change and reduce carbon emissions.

Inline Feedbacks
View all comments

Myth 6 is that a widening will substantively reduce congestion independent of induced demand. Widening to reduce congestion rests on the assumption it will reduce or eliminate periods of facility breakdown/failure. Facility breakdown being the speed at which each additional vehicle added to a roadway decreases the roadways throughput capacity in a non-linear manner. On most Interstates throughput peaks at about 45 MPH, where a lane can carry about 2200 cars per lane per hour.

comment image

You could effectively double peak period capacity (eliminate congestion) via a toll that maintains optimal operational efficiency for a fraction of the cost and time of any widening project. It’s crazy we try to meet peak demand versus smoothing demand in those brief windows. The paradox of expansion is that in the name of keeping roadways ‘free’ we end up spending more, implicitly via time loss and explicitly through massively expensive debt financed expansion projects the deliver no relief.

More attention needs to be paid to the Greenshield’s Speed Flow curve that has been around almost a 100 years, and just how elastic travel demand is. A toll to enter the highway during the peak period at less than a bus fare could likely come pretty close to eliminating congestion just by preventing the downward spiral of facility breakdown.

Gregory Quetin

I was hoping folks would be able to add to the list of myths!


Happy to contribute, I looked in vain for a paper on the marginal impact of each vehicle added to a saturated roadway. Really gets across how wasteful expansion is. The difference between peak efficiency and dismal efficiency is essentially a handful of vehicles, so long as you keep the ‘tipping point’ car out of the system everything works almost twice as well.

It’s the same logic behind the ramp metering you get in Minnesota where they’ll hold vehicles for up to 4 minutes across the network to prevent breakdown. It’s an interesting case-study, the legislature passed an act turning the lights off only to reverse when it proved just how beneficial metering was. It’s crazy expansion is pursued ever when you could get a bigger capacity boost through minor demand management.

Obviously optimizing vehicle throughput has it’s own issues, but easier to argue against expansion when there’s a cheaper, faster, and more effective alternative.


Isn’t this more or less the logic behind the HOT lanes? Vary tolls to maintain a minimum speed and run buses along the HOT corridors to provide a transit alternative to driving.


Yeah, but HOT lanes are typically pursued as independent widening projects themselves (like on 405), or HOV conversion and expansion (also 405). Operationally they work best with two lanes and I’ve never heard of GP lane(s) being reallocated to accommodate a HOT facility. Once you factor in direct access ramps to eliminate weaving etc. it’s a massive investment in auto capacity.

Also, maintaining performance is difficult since enforcing the 2+ or 3+ exemption that’s self monitored makes enforcement difficult as does the cap on tolls you get on 405 at $10. It’s why 405’s have had issues with maintaining Federally required 45 MPH.

The point I was trying to make is that widening is a really bad way to achieve the goals of its own proponents. When you hear people talk about widening, it’s almost always an economic argument and those against are naïve, ideologues, elites, etc. that aren’t concerned with how people ‘actually get around’ or economic growth. But if widening is dumb by their own economic criteria, that’s a powerful argument. I think very few realize the HOT lanes are moving about twice the vehicles at twice the speed compared to the GP lanes, instead they’re ‘Lexus Lanes.’ In a rational world, both sides of the ideological spectrum would be against expansion albeit for very different reasons.

Ideally, I think a general toll alternative should be studied on any corridor being considered for widening. While cost-benefit analysis is flawed (and biased) a toll alternative would provide a major counterpoint to the economic rhetoric employed by expansion proponents, after all, wasting money is loathed universally.


Fish aside, cars are still the #1 cause of death of *human children* in this state.

Daniel Thompson

The vast majority of voters — even in the small portion of the state where transit is a viable option — prefer to drive, for many different reasons. They tend to be higher wealth. Politicians, not transportation departments, determine where to spend transportation dollars. Some might think these citizens don’t know what is good for them, but that is tricky for a politician.

A non-myth is cars and trucks produce more economic stimulus than transit, which is important since Seattle sits on the west coast and has a port but the majority of the population lives east of the Mississippi.

I have always thought it unwise for essential services like transit to appropriate some other tangential issue for its need or funding.

Transit does not need climate change to be essential. The problem is when the tangential benefit — carbon emissions for transit (despite diesel buses) — is addressed it undermines the real primary benefit for transit which is mobility, especially for those who can only afford transit.

When transit advocates are using brake dust to argue against electric cars to support transit they have jumped the shark, and undermine transit’s true primary need. After all, what happens when cars move to a hybrid ceramic brake? Does that mean transit is no longer a tangential issue?

The other problem is when the tangential issue — climate change — harms the essential function — mobility. Metro plans to convert all its buses to electric by 2026, but the significant cost will reduce routes and frequency, which is already leading to competition among transit dependent communities for future service.

Is cleaner transit more essential than more routes and frequency? Especially if you have to use transit for mobility, and are disproportionally communities of color.

Gregory Quetin

I agree with a lot you are saying. The main conflict I see between cars and transit is space, and that space is often diverted to cars using a few of the myths outlined. I also wouldn’t claim these myths to be the best argument FOR transit, more that they are empty excuses against it. I would invest everything in more transit routes and more frequency before moving to electric (unless there was an efficient way to do it as buses retired) – making the city accessible to everyone is a awesome (and primary) goal of transit but the climate benefits are also huge. I think the idea of spending big to go to electric instead of more frequency and routes is actually just a bad analysis of what reduces carbon emissions the most.

Gregory Quetin

I would also be curious if you have a citation for cars and trucks creating more stimulus than transit, as that doesn’t match with studies I have seen.

Quiet Observer

Other considerations include the fact that the larger, articulated, and electrified transit buses are up to 5 times more damaging (higher ESALs) than a typical 18 wheeler. The Seattle pavements are not designed to carry such load. These buses often exceed the legal load limit, thus they cause distress in the pavement and cause it to break down faster. Because the pavement breaks down faster the City spends more money to keep it in a state of good repair. However, due to the increasing maintenance and more frequent reconstruction these buses are creating more carbon emissions. Often these considerations aren’t factored into the return on investment when transit agencies “Go big”. I would like this to be reported more often. Transit services are part of the solution as well as part of the problem. Cars are part of the solution as well as part of the problem. We need to find ways to work together to solve today’s transportation challenges designing solutions and strategies to mitigate our collective risk while ensuring sustainable and equitable transportation options for future generations.


With regard to “tire and brake particles…” My understanding is that electric car brakes don’t work like the brakes of conventional cars. Rather than rubbing an abrasive surface against the wheels to slow the car down (which may emit particles), electric cars simply reverse the motor so that it acts as a generator, pumping the car’s kinetic energy right back into the battery. While I believe conventional brakes do exist also, they are only used for emergency stops, not for ordinary driving, especially in the newer EV models.

So, if the cars are electric, I’m having trouble seeing where the “brake particle” emissions comes from.


They would then still be an issue, just a smaller one if regenerative braking mean less rubbing than traditional braking?

Douglas Trumm

EVs very much still create particulate pollution. Regenerative braking helps but not as much as you’re suggesting. For one, it helps with the brake pad issue, but less so with the tires themselves, which are the source of salmon killing compounds. Additionally, cars kick up and stir up particulate matter on the roadway simply by zooming by. Moreover, electric cars tend to be heavier due to their large battery and that adds strain to the brakes and tires and can erase the advantage of regenerative braking if the car is heavy enough, as OECD research shows:

“Electric vehicles are estimated to emit 5-19% less PM10 from non-exhaust sources per kilometer than internal combustion engine vehicles (ICEVs) across vehicle classes. However, EVs do not necessarily emit less PM2.5 than ICEVs. Although lightweight EVs emit an estimated 11-13% less PM2.5 than ICEV equivalents, heavier weight EVs emit an estimated 3-8% more PM2.5 than ICEVs.” -OECD report

An electric Hummer or F150 is still a massively polluting vehicle. Meant to cite this study but forgot to include the link so I’ll add here and include in the piece:

Paul W.

Remote working is reducing driving around here, and the reductions are substantial. WFH will persist. Highway congestion will be reduced by the new employment realities around here. [Moderator: Traffic congestion is rebounding, see here:

The premise of “Myth 3” is bassackward. People are leaving Seattle [Moderator: This is false. More are moving here than leaving.], especially the central part of it. That will continue as employers no longer will be demanding daily commutes of their workforces.

Light rail expansion plans here should be halted. There won’t be enough people residing near light rail stops who need to the train often enough to locations within a quarter mile of other light rail stops. [Citation needed] It won’t be “green” because it will be transporting mostly air, and not people who otherwise would be driving.


You just countered Myth 3 by invoking Myth 5.