What Really Happens When Road Space is Reallocated from Cars

Have you ever wondered what happens when lanes or roads designed for cars are repurposed for buses, bikes and pedestrians? This concept is known as “traffic evaporation” and it offers insights into how cities can reimagine their transportation systems. By understanding traffic evaporation, city planners and officials can make informed decisions about reallocating road space to support sustainable modes of transport like walking, biking and public transit.

Traffic Doesn’t Just “Disappear” – It Evaporates

The term “traffic evaporation” refers to the phenomenon that occurs when road space is reduced or reallocated. Contrary to expectations, reducing capacity does not always result in traffic jams. Instead, some of the traffic seems to just “disappear”. This happens because people adjust their travel choices – like driving at different times, taking other routes, using other modes like public transport, bikes or walking, or simply deciding not to make certain trips.

How Traffic Evaporation Occurs

There are several key factors that contribute to traffic evaporation when road space is reallocated:

• Mode Shift: Some people will shift to other modes like public transit, biking or walking when space for cars is reduced. For example, new protected bike lanes or bus rapid transit lines provide attractive alternatives to driving.
• Route Changes: Drivers may alter their routes to avoid new congested areas. GPS and traffic apps make it easy to find alternative routes.
• Departure Time Changes: Drivers can shift the timing of their trips to avoid peak congestion periods. Flexible work schedules and off-peak deliveries enable this.
• Destination Changes: People may change trip destinations to someplace closer or more accessible by alternative modes. For example, choosing local stores vs driving across town.
• Trip Consolidation: People can link together multiple errands into one tour or share rides with others, reducing total vehicles on the road.
• Trip Frequency Changes: Cutting out optional or marginal trips that are low priority. For example, eliminating a low-value errand.
• Long-Term Land Use Changes: Over years, land use patterns may shift as development concentrates in areas accessible by sustainable modes. For example, transit-oriented development.

Travel Behaviors Are Flexible

The key insight is that travel demand is quite flexible. If the built environment changes or conditions shift, people have a variety of ways to adapt through changes in mode, timing, route, destination, trip chaining, frequency, car sharing and more. So adding new attractive sustainable travel options while reducing road space incentivizes these adaptations.

Examples of Traffic Evaporation in Action

There are many real-world examples that demonstrate the traffic evaporation effect when road space is reallocated. Here are some prominent cases:

New York City, Broadway

One of the best known examples is in New York City, when Broadway between Times Square and Herald Square was closed to vehicles in 2009. The project repurposed 3.2 kilometers of lanes previously dedicated to vehicles as pedestrian plazas. Despite fears of gridlock, actual traffic congestion never materialized. Vehicle travel times on north-south avenues improved 17% and travel speeds increased by 7% even though street capacity decreased 11%.

Seoul, Korea, Cheonggye Freeway Removal

In Seoul, South Korea, a busy elevated freeway was demolished in 2005 and the roads underneath were converted to a 3.6 mile long linear park along the Cheonggyecheon River. Despite removing a major car corridor that carried 168,000 vehicles per day, traffic issues never arose. With advanced publicity and planning, most drivers adapted by changing routes, departure times and modes. Vehicle kilometers traveled in the corridor declined, but overall traffic volumes across Seoul remained stable.

San Francisco, Embarcadero Freeway Removal

In San Francisco, the double-deck Embarcadero freeway was demolished in 1991 after being damaged in an earthquake. Instead of rebuilding it, the city replaced the freeway with a boulevard at street level. Prior fears of gridlock did not materialize. Traffic congestion dissipated quickly. And the waterfront area revitalization catalyzed billions in new investment and economic activity.

Minneapolis, Nicollet Mall

The Nicollet Mall in downtown Minneapolis was converted to a transit and pedestrian zone in the 1970s. Vehicle cross traffic was banned while maintaining access for deliveries and parking garage entrances/exits. Despite removing 50,000 vehicles per day, people adapted easily by dispersing to alternative streets and switching modes. Traffic capacity on parallel streets increased without congestion issues. The transit mall was so successful it was expanded.

Paris, Georges Pompidou Expressway and Riverbank Highways

In Paris, sections of the Pompidou Expressway along the Right Bank of the River Seine were closed to vehicles and converted into linear parks beginning in 2001. Other riverbank highways were also removed. Traffic redistributed to other city freeways and arterials without notable congestion. The lively public spaces improved the area and spurred economic development.

New York City, Herald Square Pedestrianization

In New York City, sections of Herald Square at the intersection of 34th Street, 6th Avenue and Broadway were pedestrianized in 2016. Despite concerns about diverting traffic, minimal congestion resulted. Drivers were able to divert to adjacent lanes or arterials. Walking, transit and business activity increased considerably.

Barcelona, Superblocks Program

The city of Barcelona initiated an innovative Superblocks program in 2016. It aims to convert multiple groups of city blocks into shared spaces for walking, biking and community interaction while diverting through traffic to perimeter roads. Early Superblocks implemented have generated minimal traffic impacts while increasing public space, walking, biking and community life.

Boston, Commonwealth Ave

Boston implemented a pilot in 2017 to re-allocate vehicle lanes on Commonwealth Ave as new protected bike lanes. Despite removing 33% of car lanes in each direction, average vehicle travel times only increased modestly during peak hours – by 25-50 seconds along most of the corridor. Overall traffic volumes declined slightly as some drivers shifted routes or departure times.

Seattle, 2nd Ave Protected Bike Lane

In 2014, a protected two-way bike lane was installed on Seattle’s Second Avenue which reduced a four-lane one-way street to two lanes. Despite concerns about congestion, the changes resulted in minimal impacts on vehicle travel times or congestion. Travel times remained steady or even improved. Vehicle volumes decreased but overall traffic efficiency increased.

London, Congestion Charging Scheme

In 2003, London implemented a congestion charge for vehicles entering the central city area. The scheme reduced traffic volumes entering the zone by 15%. Travel speeds inside the zone improved while delays were reduced. Traffic increased slightly on the boundary roads but without notable congestion. The scheme was successful in reducing traffic volumes and raising revenue for public transport.

Stockholm, Congestion Pricing Trials

Stockholm implemented a congestion pricing trial from 2006-2009 with fees to drive in the inner city. Traffic volumes reduced 20% and delays decreased 30-50% within the zone. After the trial ended, the congestion pricing program was made permanent due to its success. Traffic volumes remained reduced while transit, biking and walking activity increased.

Netherlands, “Living Street” Shared Spaces

Many cities in the Netherlands have implemented “Living Street” shared spaces where vehicle, pedestrian and bike traffic mix slowly using subtle urban design cues instead of traffic controls. This maintains access while decreasing dominance of cars. Living Streets have resulted in improved safety, lower traffic speeds, reduced congestion and increased community interaction.

Portland, Streetcar System

Portland’s streetcar system reallocates road space to transit while also acting as a catalyst for transit-oriented development. Since opening in 2001, the streetcar has spurred over $4 billion in investment within two blocks of stops. Ridership continues to increase without notable car traffic congestion as people switch modes. The streetcar demonstrates the power of transit to shape cities.

Reasons Why Traffic Evaporation Occurs

There are several key reasons why traffic evaporation has occurred in cities worldwide when road space is allocated from cars to other uses:

1. Overestimating Traffic Impacts

Engineers often overestimate the traffic impacts when road space is reallocated. Traditional traffic modeling focuses heavily on vehicle throughput and underestimates how flexible people’s travel behavior can be. This contributes to overblown fears about congestion that rarely materialize.

2. Induced Demand From Road Expansion

When roads are expanded, additional traffic is “induced”, filling the new capacity over time and often resulting in the same level of congestion. Conversely, traffic evaporation occurs when road space is reduced as people adapt and shift modes.

3. Braess’s Paradox – More Roads Can Equal More Congestion

Braess’s Paradox states that adding road capacity can sometimes increase congestion over time by inducing more demand. Similarly, removing roads can reduce demand and thus congestion. Traffic evaporation demonstrates this paradox.

4. Downs-Thomson Paradox – Traffic Expands to Fill Space

The Downs-Thomson Paradox states that traffic expands to fill the space available. So if space is reduced, traffic shrinks to fit the new space. Traffic evaporation illustrates this effect.

5. Multiple Route and Mode Choices

In urban networks with many route options, traffic can redistribute efficiently when road space is reallocated. Similarly, multiple modes like transit provide alternatives.

6. Advanced Traveler Information Systems

Navigation apps and real-time traffic information allows drivers to adapt to congestion by changing routes, departure times and modes to avoid delays.

7. Flexible Work Schedules + Delivery Times

Work and freight shifts to non-peak times reduce peak congestion. With rising flexwork and off-peak delivery, peak demand is decreasing.

8. Demand Not Infinite

Assumptions that demand for car travel is endless are wrong. When driving is constrained, people prioritize trips and adapt. There is not infinite demand.

9. Latent Demand For Sustainable Modes

If good alternatives like transit and biking are available, many prefer to use them. Reallocating road space unlocks this latent demand for sustainable modes.

10. Demand Dependent on Design

People’s choices depend on the built environment and options available. Redesigning cities for sustainable modes induces demand away from cars.

Benefits of Re-Allocating Road Space

There are many potential benefits to cities from implementing road space reallocation projects informed by traffic evaporation insights:

• Less Traffic Congestion: Counterintuitively, reducing space for cars can decrease congestion as people shift modes. This improves mobility, reduces pollution and increases safety.
• More Sustainable Transportation: Enabling walking, biking and public transit improves health, reduces carbon emissions and benefits mobility access.
• Safer Streets: Lower traffic speeds and volumes make roads safer for all users, especially pedestrians and bikers. This reduces crashes and fatalities.
• More Public Space + Community: Reclaiming roads for people creates vibrant public spaces for community interaction and promotes economic development.
• Cleaner Air + Lower Noise: Reducing car traffic improves air quality, lowers noise pollution and enhances quality of life. This has major health benefits.
• Higher Quality of Life: Cities become more livable, healthy, sustainable and people-oriented by prioritizing walking, transit and public space over cars.

Implementing Road Space Reallocation Projects

For cities interested in reallocating road space, here are some recommendations for implementation:

Conduct Rigorous Traffic Analysis

Conduct data-driven studies using valid statistical methods to determine baseline traffic patterns and robustly model impacts. Avoid exaggerating congestion fears.

Engage Stakeholders Early + Often

Consult impacted businesses, residents, agencies and users early, frequently and transparently. Dispel misconceptions through education and facts.

Phase In Changes Over Time

Stage implementation in phases to allow people to gradually adapt travel patterns. For major projects, do temporary pilots first to demonstrate benefits.

Focus on Equity + Access

Prioritize equity, access and mobility justice. Accommodate the needs of deliveries, disabled people, essential trips, seniors and disadvantaged groups.

Promote Alternatives + Enable Adaptation

Boost sustainable alternatives like transit and biking to enable adaptation. Provide wayfinding, alerts, incentives and support programs.

Manage Roads Dynamically

Monitor traffic and adapt signals, lane configurations and other infrastructure dynamically to improve flow as patterns change. Don’t just set it and forget it.

Enforce Laws + Regulations

Enforce road rules and parking/loading regulations to manage demand. For example, keep bike and transit lanes clear during peak periods.

Learn + Refine

Collect data and user feedback continuously. Make changes and improvements over time. Be flexible and responsive to optimize outcomes.

Key Takeaways

The concept of traffic evaporation has profound implications for transportation planning and policy. Here are some key insights to keep in mind:

• Traffic demand is flexible and adaptable, not infinite
• Road expansion often backfires, while road reduction can improve flow
• Overestimating traffic impacts leads to distorted decisions
• Induced demand works both ways – add lanes or reduce lanes
• Multiple route choices distribute traffic efficiently
• Advanced traveler information enables adaptation
• Flexwork and off-hour delivery flatten peaks
• There is latent demand for walking, biking and transit
• Designing cities for sustainable modes induces demand away from cars
• Removing road space provides benefits like less congestion, cleaner air, safer streets, more vibrant public spaces and higher quality of life
• With careful planning and phasing, traffic evaporation allows road space reallocation to create more livable cities

In summary, traffic evaporation offers a new model for mobility in sustainable cities. By harnessing lessons from pioneering urban road space projects around the world, cities can reimagine streets for people, not just cars. Understanding how traffic adapts when road space is reallocated is crucial knowledge for effective transportation planning. The results can transform cities to be more livable places for all.

Conclusion: Rethinking Roads to Revitalize Cities

The examples and analysis of traffic evaporation presented demonstrate how cities around the world have successfully reallocated road space from cars to more sustainable modes of walking, biking and public transit. Despite widespread expectations of gridlock and congestion, in case after case traffic has evaporated as people adapt in reasonable and predictable ways.

These real-world experiments embody powerful principles from Braess’s Paradox to Downs-Thomson Paradox. The findings challenge long held assumptions that traffic demand is infinite and rigid. In fact, travel behavior is flexible and strongly shaped by the built environment. Cities designed for cars induce more driving, while cities designed for people unlock latent demand for sustainable mobility.

With accurate modeling and phased implementation, traffic evaporation enables reimagining urban roads. The benefits are multifold – improved safety, air quality, mobility access, public spaces, quality of life and more. The common narrative that removing roads causes congestion is often false. Done right, road space reallocation creates people-centered cities where communities flourish.

For too long, cities have catered to cars at the expense of livability and sustainability. Traffic evaporation points the way to a new vision of urban mobility. With innovation, careful planning and community engagement, urban road projects can redistribute space to better serve all users.

Streets make up a large share of public space in cities. Reallocating a portion of this precious resource to expand sidewalks, bike lanes, bus lanes, parks and plazas allows cities to become vibrant human habitats again. Traffic evaporation makes this possible without gridlock.

The path forward requires policymakers and planners to incorporate lessons from successful road space reconfiguration projects. With open minds and sound data, the feared traffic impacts rarely materialize. The supposed mobility catastrophe fails to unfold. Instead, cities are revitalized as communities adapt to reimagined streets.

Traffic evaporation upends entrenched car-centric assumptions about mobility in cities. The knowledge that traffic demand can shrink when road space does provides cities worldwide with an opportunity to transform urban landscapes for the better. The evaporating traffic enables reallocation to create more livable public spaces that improve health, equity, access, environment, safety, economics and quality of life in profound ways. When implemented thoughtfully, these projects demonstrate the power of rethinking roads to revitalize cities for all. Traffic evaporation unlocks this enormous potential.