Can public transport investment really fix traffic congestion?

Well, this is fine: traffic in the north west Chinese city of Xi'an on a smoggy day. Image: Getty.

Now and then, someone mentions that a particular transit project did not reduce traffic congestion, as though that were evidence of failure.

In fact, the relationship between transit and congestion is an indirect one. In most cases, it’s unwise to claim congestion reduction as a likely result of your proposed transit project. (In this post “congestion” means that volume/capacity ratio for motor vehicles on a roadway is high enough to substantially reduce average speeds.)

Road widening, however, is also not a very good way to relieve congestion, except in the short term. In his 1992 book Stuck in Traffic Anthony Downs described the effect of widening an expressway in terms of a “triple convergence”:

In response, three types of convergence occur on the improved expressway:

(1) many drivers who formerly used alternative routes during peak hours switch to the improved expressway (spatial convergence);

(2) many drivers who formerly travelled just before or after the peak hours start travelling during those hours (time convergence); and

(3) some commuters who used to take public transportation during peak hours now switch to driving, since it has become faster (modal convergence).

Downs is describing only the immediate effect of the road expansion. Further increases in traffic will come from any new development that is attracted to the road’s catchment as a direct consequence of its expansion.

Prof. David Levinson’s work in the Minneapolis / St. Paul region suggests that, while added capacity generates new vehicle trips, the effect is often not great enough to restore the previous level of congestion. However, your results will obviously vary based on the amount of development that occurs as a result of the new or expanded road. If this development adds enough new vehicle trips to fill the new capacity, traffic congestion can return to near previous levels.

So the only way to make the congestion benefit of new road capacity permanent is to severely restrict development in the catchment area of the road – an impossible bar in most cases. In fact, parties who will profit from further development in a corridor may be part of the political consensus in support of a road expansion, even as the same expansion is marketed to existing residents as a congestion reducing project.

Otherwise, there appear to be two broadly applicable ways to relieve congestion in a substantial and permanent way.

Economic collapse. Traffic congestion drops during economic slowdowns, because fewer people have jobs to commute to, or money to spend on discretionary travel. A complete economic collapse, which causes people to move away from a city in droves, is always a lasting fix for congestion problems.

Correct pricing of road space. Fundamentally, congestion is the result of underpricing. If you give away 500 free concert tickets to the first 500 people in line, you’ll get 500 people standing in line, some of them overnight. These people are paying time to save money.

Current, prevailing road pricing policy requires all motorists to act like these frugal concertgoers. Motorists are required to pay for road use in time, rather than in money, even though some would rather do the opposite – and our cities would be safer and more efficient if they could. Current road pricing policy requires motorists to save money, a renewable resource, by expending time, the least renewable resource of all.

So if transit isn’t a cause of reduced congestion, what is its role? Do transit advocates offer nothing in response to congestion problems that have many voters upset?

In fact, transit’s role is essential, but its effect is indirect.


1) Transit raises the level of economic activity and prosperity at a fixed level of congestion.

Congestion appears to reach equilibrium at a level that is maddeningly high but that can’t be called “total gridlock.” At that level, people just stop trying to travel. If your city is car-dependent, that limit becomes the cap on the economic activity – and thus the prosperity – of your city. To the extent that your city is dependent on transit, supported by walking and cycling, economic activity and prosperity can continue to grow while congestion remains constant.

To quite a comment left on my website, on an earlier version of this post: “Toronto achieved significant downtown employment growth without increasing road capacity after the 1960s, thanks first to increased subway ridership and later due to increased commuter rail ridership. Congestion is still bad on the roads and expressways into downtown, even with transit expansion, but the expansion of transit has permitted the downtown to grow beyond what the road network would have supported.” A similar pattern can be observed in many similar cities.

2) Transit enables people who can’t drive to participate in economic life.

Groups who don’t have the option to drive include many seniors and disabled persons, some youth, and a segment of the poor. Providing mobility to these groups is not merely a social service; it also expands participation in the economy.

For example, during the US welfare reform debate in 1994-96, government began raising pressure on welfare recipients to seek and accept any employment opportunity. For the very poor living in car-dependent cities, the lack of commuting options became a profound barrier to these job placements.

This is really an element of the previous point, since all employment, even of the poor, contributes to prosperity. But this has independent force for government because unemployed people consume more government services than employed people do. This benefit of transit should routinely be described in terms of economic efficiency, as I’ve done here, rather than appealing to pity or to alleged “economic rights,” as social-service language often implicitly does. The appeal of the social service argument is just too narrow, especially in the US.

Hey, at least the train is moving: just another rush hour in Manila. Image: Getty.

3) Transit-dependent cities are generally more sustainable than car-dependent cities.

They cover less land and tend to have fewer emissions both per capita and per distance travelled. The walking that they require is also better for public health, which produces further indirect economic benefits in reduced healthcare costs.

4) Intense transit service is essential for congestion pricing.

Congestion pricing appears to be the only effective and durable tool for ensuring free-flowing roads while maintaining or growing prosperity. Congestion pricing always causes mode shift toward public transit, so quality public transit, with surplus capacity, must be there for a pricing plan to be credible.


5) Surface exclusive transit lanes (for buses, rail, and arguably two-wheelers and taxis) improve the performance of emergency services.

This argument should be much more prominent, because even the most ardent car-lover will understand it. Few things are more distressing than to see an emergency vehicle stuck in traffic, sirens blaring. When confronted with this, all motorists do their best to help. But if the entire width of a street or highway is reserved for cars (moving or parked), and is therefore capable of being congested, it can be impossible to get out of the way of an emergency vehicle even if every motorist present has the best of intentions.

Emergency response should be one of the strongest and most obvious cases for surface transit lanes. Motorists understand the need to drop to a low speed in school zones, to protect the life of every single child. Why do we not accept come degree of delay to save a child who may be dying somewhere else, because the ambulance is stuck in traffic?

In the end, of course, “congestion” is not a good measure of the outcomes of transit. In fact, the very notion of congestion presumes a motorist’s view of the world. I agree with another commenter, Rodrigo Quijada, when he writes:

What we’d like to do in a city is to reduce TRAVEL TIMES. Reducing congestion is a way to do that, but in no way the only one. Over the decades, in places where car transportation has become dominant, people have got used to see travel times and congestion as the same thing, thus orienting their thinking and their solutions to reduce congestion. But this is essentially a confusion.

Still, in real-world transit politics, selling transit projects to current motorists is a necessity, and the current motorist is likely to see her problem as one of congestion. So it’s important to be clear on what transit can readily do for her.

  1. It can provide an alternative to driving which may be faster, more cost effective, and less stressful. This argument can be put quite selfishly: Good transit won’t eliminate congestion in your city, but it can eliminate it from your daily life.
     
  2. Transit helps reduce government spending on social services by enabling transit disadvantaged groups to participate in the economy. This obviously has a range of health and wellness benefit apart from its economic role.
     
  3. It can increase the level of prosperity at a fixed level of congestion.
  1. Its exclusive lanes protect emergency vehicles from congestion-related delays, potentially saving lives.

Jarrett Walker is an international consultant in public transit network design and policy, based in Portland, Oregon. He is also the author of “Human Transit: How clearer thinking about public transit can enrich our communities and our lives".

This article was originally written for his blog, and is reposted here with permission.

 
 
 
 

Green roofs improve cities – so why don’t all buildings have them?

The green roof at the Kennedy Centre, Washington DC. Image: Getty.

Rooftops covered with grass, vegetable gardens and lush foliage are now a common sight in many cities around the world. More and more private companies and city authorities are investing in green roofs, drawn to their wide-ranging benefits which include savings on energy costs, mitigating the risk from floods, creating habitats for urban wildlife, tackling air pollution and urban heat and even producing food.

A recent report in the UK suggested that the green roof market there is expanding at a rate of 17 per cent each year. The world’s largest rooftop farm will open in Paris in 2020, superseding similar schemes in New York City and Chicago. Stuttgart, in Germany, is thought of as “the green roof capital of Europe”, while Singapore is even installing green roofs on buses.

These increasingly radical urban designs can help cities adapt to the monumental challenges they face, such as access to resources and a lack of green space due to development. But buy-in from city authorities, businesses and other institutions is crucial to ensuring their success – as is research investigating different options to suit the variety of rooftop spaces found in cities.

A growing trend

The UK is relatively new to developing green roofs, and governments and institutions are playing a major role in spreading the practice. London is home to much of the UK’s green roof market, mainly due to forward-thinking policies such as the 2008 London Plan, which paved the way to more than double the area of green roofs in the capital.

Although London has led the way, there are now “living labs” at the Universities of Sheffield and Salford which are helping to establish the precedent elsewhere. The IGNITION project – led by the Greater Manchester Combined Authority – involves the development of a living lab at the University of Salford, with the aim of uncovering ways to convince developers and investors to adopt green roofs.

Ongoing research is showcasing how green roofs can integrate with living walls and sustainable drainage systems on the ground, such as street trees, to better manage water and make the built environment more sustainable.

Research is also demonstrating the social value of green roofs. Doctors are increasingly prescribing time spent gardening outdoors for patients dealiong with anxiety and depression. And research has found that access to even the most basic green spaces can provide a better quality of life for dementia sufferers and help prevent obesity.

An edible roof at Fenway Park, stadium of the Boston Red Sox. Image: Michael Hardman/author provided.

In North America, green roofs have become mainstream, with a wide array of expansive, accessible and food-producing roofs installed in buildings. Again, city leaders and authorities have helped push the movement forward – only recently, San Francisco created a policy requiring new buildings to have green roofs. Toronto has policies dating from the 1990s, encouraging the development of urban farms on rooftops.

These countries also benefit from having newer buildings, which make it easier to install green roofs. Being able to store and distribute water right across the rooftop is crucial to maintaining the plants on any green roof – especially on “edible roofs” which farm fruit and vegetables. And it’s much easier to create this capacity in newer buildings, which can typically hold greater weight, than retro-fit old ones. Having a stronger roof also makes it easier to grow a greater variety of plants, since the soil can be deeper.


The new normal?

For green roofs to become the norm for new developments, there needs to be buy-in from public authorities and private actors. Those responsible for maintaining buildings may have to acquire new skills, such as landscaping, and in some cases volunteers may be needed to help out. Other considerations include installing drainage paths, meeting health and safety requirements and perhaps allowing access for the public, as well as planning restrictions and disruption from regular ativities in and around the buildings during installation.

To convince investors and developers that installing green roofs is worthwhile, economic arguments are still the most important. The term “natural capital” has been developed to explain the economic value of nature; for example, measuring the money saved by installing natural solutions to protect against flood damage, adapt to climate change or help people lead healthier and happier lives.

As the expertise about green roofs grows, official standards have been developed to ensure that they are designed, built and maintained properly, and function well. Improvements in the science and technology underpinning green roof development have also led to new variations on the concept.

For example, “blue roofs” increase the capacity of buildings to hold water over longer periods of time, rather than drain away quickly – crucial in times of heavier rainfall. There are also combinations of green roofs with solar panels, and “brown roofs” which are wilder in nature and maximise biodiversity.

If the trend continues, it could create new jobs and a more vibrant and sustainable local food economy – alongside many other benefits. There are still barriers to overcome, but the evidence so far indicates that green roofs have the potential to transform cities and help them function sustainably long into the future. The success stories need to be studied and replicated elsewhere, to make green, blue, brown and food-producing roofs the norm in cities around the world.

Michael Hardman, Senior Lecturer in Urban Geography, University of Salford and Nick Davies, Research Fellow, University of Salford.

This article is republished from The Conversation under a Creative Commons license. Read the original article.