10.4 Transportation

One of the defining features of cities is traffic. All the people working, shopping, and spending time downtown need to get around, and many people who live in surrounding suburbs commute to and from the city center. That means a lot of cars, often with only one person in them, emitting greenhouse gases and air pollution as they idle in traffic jams. Globally, transportation is the second-largest source of GHG emissions, not counting land use change.^[1] Some city planners have tried to deal with congestion by building bigger roads with more lanes, but this creates induced demand – because there’s more space, more people drive on those roads, and before long, they’re as congested as they were before the expansion (Fig 1).

Vehicles are a major source of both water and air pollution, and vehicle infrastructure (impervious roads and parking lots) increases stormwater runoff and urban heat islands. Driving damages our health in other ways as well, including physical inactivity, social isolation, stress, noise pollution, and injuries from vehicle accidents. Physical inactivity contributes to obesity and other diseases, and people who drive tend to have a higher body mass index than people who use more active modes of transportation.^[2]

For the many people who can’t drive (too young or too old, have a disability, can’t afford a car), living in a place where driving is the only feasible transportation option means having limited access to jobs, activities, grocery stores, and social connections. Roads that are built through existing neighborhoods can similarly limit access and isolate people. Car commuters also have to deal with sitting in traffic, searching for parking, and sometimes conflict with other drivers, all of which cause stress. People living and working near loud roads have to deal with noise pollution, which causes so much harm to physical and mental health that its disease burden is comparable to that of second-hand smoke. Finally, road travel crashes cause millions of deaths and tens of millions of injuries around the world every year (see footnote #2 for more on all these health impacts).

Public transit can solve many of these problems if it is designed well. Routes have to connect housing to destinations and destinations to each other. Different modes of transport have to be well integrated in space, time, and payment (like having one access card that works on all modes of transportation) so that passengers can easily switch between them. Transit has to come often and on time, and it has to be straightforward to use (app, tickets, etc.). It has to be at least as convenient as driving, which typically means, among other things, getting people to their destinations faster. Metros and many tram systems have this advantage since they are separate from traffic, but tunnels and tracks are very expensive to build.

Even in cities growing large enough to need extensive transit systems, governments may be reluctant to invest in those travel modes. Buses do not require nearly as much new infrastructure, but they often get stuck in traffic. Bus rapid transit (BRT) systems solve this problem by giving buses their own lanes and sometimes priority at intersections. You can click here for an in-depth look at one of the longest-running BRT systems, in Curitiba, Brazil, which includes specially designed metro-like bus stations that allow for prepaid, same-level boarding. Figure 2 shows the share of the urban population in each country with convenient access to public transit, as of 2022.

Active transportation (walking, biking, etc.) provides healthy physical activity, produces zero emissions, and takes up less space than cars. As any pedestrian or cyclist knows, some parts of cities are much more walkable and bikeable than others. Pedestrians and cyclists need designated space (sidewalks and bike lanes) so they don’t have to dodge cars as they go. Cyclists need bike racks to park at, located conveniently and protected from weather (Fig 3). Pedestrians appreciate having benches to rest on, as well as shade (trees, awnings, or constructed shelters) for hot days. People with physical disabilities need accessibility infrastructure like sidewalk curb cuts (which also benefit cyclists) and ramps.

However, physical infrastructure is not enough to create a large-scale shift toward active transportation. Walking and biking need to be accepted culturally, and people need to feel safe while doing them. Many people avoid walking, at least in certain areas, because they fear harassment or crime. Cultural shifts and improvements to public safety can thus also facilitate shifts to sustainable lifestyles. In many parts of the world, cycling is associated with poverty, and in others, people see it as a form of exercise but not daily transportation. In some cultures, however, it’s seen as a normal and respectable way of getting around; Denmark, for example, is known for having government officials who commute by bike. You can click here for an interesting blog post on the contrast between cultural attitudes toward biking in Tehran, Iran, and Amsterdam, the Netherlands. For ideas on how to nurture a bike-positive culture, you can read this article.

Once a city has good alternatives to cars available, it can start making driving a less appealing option. Since giving cars more space increases the number of people driving, logically, giving them less space will make more people choose other modes of transportation. Many European cities are doing this, in a variety of ways. Paris, France has banned motorized through-traffic in the city center. Barcelona, Spain has created ‘superblocks:’ only a wide grid of streets is open to cars, and the smaller streets within each large square are reserved for pedestrians and cyclists.

Delft, the Netherlands created the ‘woonerf,’ or ‘living street,’ method of managing transportation, which is actually the reverse of the previous approaches because it removes the divide between car and pedestrian space. Woonerf streets don’t have sidewalks, and instead, pedestrians, bikes, and cars all share the same space, which forces drivers to go slowly and give priority to others. Cities in South America are also shifting from car-centric to people-centric streets. You can watch this interview with the Minister of Public Space and Urban Hygiene of Buenos Aires, Argentina about improving walkability. Most recently, New York City has implemented congestion pricing, charging drivers to enter the city center, and the first few months have shown decreased traffic, accidents, noise complaints, and school bus delays and increased bus use and speeds.^[3]

When people drive less, cities don’t need as much space for parking, and that space can be used to increase density or natural areas. For the vehicles that remain, cities can encourage people to choose low- or zero-emissions vehicles by providing convenient charging infrastructure (Fig 4) and establishing low-emissions zones (Fig 5). Electrifying bus fleets is also a key step, as Santiago, Chile is modelling.^[4] Cities can also set up car and bike share programs, which reduce people’s need to own their own vehicles and are useful for tourists.

You can click here for an 11-minute video on entrenched car culture, essential features of usable public transit systems, and ways to disincentivize driving, with examples from Jakarta, Indonesia and several European cities.

Knowledge Check

Take a moment to complete the short quiz below to assess your understanding of this section. Read each question carefully and refer to the section content as needed. This quiz is not graded – it’s simply an opportunity for you to reflect on what you’ve learned and reinforce key concepts.