Traffic congestion threatens to drive up emissions and cripple economies unless global leaders act on sustainable transportation solutions, a group of experts warned yesterday.

Rapid urbanization, particularly in the developing world, is driving the need to address sustainable transportation, said Holger Dalkmann, director of the World Resources Institute's EMBARQ program on financially and environmentally sustainable transportation.

"For the first time, last year, we had more people living in cities than in rural areas. In China, in particular, we now have more people living in cities than urban areas, and India will get there by 2040," he said yesterday at the Transforming Transportation 2013 conference. "So how we develop cities now will heavily influence the footprint of the city, but also how people will move and their quality of life."

The way a city grows could lock in a dependence on cars, as in sprawling Los Angeles, or stimulate the use of alternative, low-carbon modes of transportation, like the bus rapid transit system on the arterial streets of Curitiba, Brazil.

Experts say the urgency to address sustainable transportation is underscored by a new pace of economic development, which in many places is causing cars to outpace population growth.

Nikolay Asaul, Russian deputy minister for transport, said yesterday that the population of Russia is increasing by 1 percent per year, while the number of vehicles is increasing at 2.5 percent per year. In Quito, Ecuador, the number of inhabitants is growing by 2 percent, while the number of cars is increasing by 8 percent, said Mayor Augusto Barrera.

"We need to accept that there's an incredible aspirational issue here," said Rakesh Mohan, chairman of India's National Transport Development Policy Committee. "People that are just getting into income levels where they can afford personalized transport are going to have it."

Drawing the masses toward alternative transportation requires overcoming cultural, political and financial barriers, but momentum is starting to grow.

Ten years ago, transport was nowhere to be found on the sustainability agenda. Last year, it was one of the most important topics discussed at the U.N. Conference on Sustainable Development in Rio de Janeiro, or Rio+20, where eight of the world's largest multilateral development banks made an unprecedented commitment of $175 billion toward sustainable transportation over the next decade.

Defining 'sustainable'

Yesterday, EMBARQ and the C40 Cities Climate Leadership Group launched a partnership to tackle greenhouse gas emissions from urban transportation through sustainable urban planning, bus rapid transit systems and nonmotorized transit initiatives.

"This new partnership with EMBARQ and its global network of transportation expertise will accelerate the work cities are doing to implement more efficient and effective transit systems," New York City Mayor and C40 Chairman Michael Bloomberg said in a statement. "By combining the forces of two organizations that know how to get things done we will help provide greater transit options that will help us build a more sustainable planet."

But what exactly is sustainable transportation? For starters, it's about more than roads and buses and rail cars, and has also to do with energy security, climate change and poverty, said Jose Luis Irigoyen, director of transport, water and information and communications technologies at the World Bank.

"For us it means safe, clean and affordable transport that produces development, and this development is what we're seeing now through the framework of 'inclusive green growth,'" he said in an interview at the EMBARQ conference. "It has to be development that is inclusive, that brings people together, that addresses poverty and avoids fragmentation in society, and at the same time that balances the consequences our interventions today will have in the future."

How an institution defines sustainable transportation could have a significant impact on how it's addressed, said Robert Guild, director of the Asian Development Bank's (ADB) Transport, Energy and Natural Resources Division.

To the ADB, a sustainable transportation project is accessible, affordable, efficient, environmentally sustainable and safe. But whether or not all of those criteria must apply for the bank to make an investment is unclear.

"Can you have something that is safe and affordable but increases emissions, and does that still count? Maybe," said Guild. "Coming to convergence on the definitions and requiring those as part of strategies is, I think, part of this policy dialogue we have to have with our client governments."

Representatives of the Inter-American Development Bank and Corporación Andina de Fomento echoed their support for sustainable transportation projects, but also highlighted the need to work with all levels of government and nongovernmental groups to drive support for their investments.

Making cities competitive, clean

Sustainable transportation projects often hit a roadblock if they are seen to come in conflict with the speed or efficiency of city operations, which would cause economic damage. Investing in roads and highways would seem to get people to work faster, but experts asserted yesterday the opposite is true.

"I would argue that there is a strong win-win situation," said EMBARQ's Dalkmann on the relationship between sustainable transportation and economic growth.

"On the one hand, it's not just about moving people, but making cities attractive so that they retain people," he said. "The most competitive cities in the world are where people want to go, and where business is thriving is also in cities where there is a high quality of life through sustainable urban planning and transport."

"In the city context, it is very clear that there is no conflict," said the World Bank's Irigoyen on the introduction of sustainable transportation solutions. "We see congestion, for example, stopping a city. So we know that the solution to that problem will also be good from an economic perspective and a climate perspective."

The transportation sector as a whole accounts for roughly 13 percent of global greenhouse gas emissions. As a result, panelists at yesterday's conference made the case for transportation projects to receive support from sources such as the Green Climate Fund.

The $100-billion-per-year investment to the fund would only go a short distance toward solving the world's transportation issues, even if none of it went to other climate-related sectors such as energy and water. But climate finance can help leverage other funds that could have a huge cumulative impact, said Dalkmann.

If the world is to effectively tackle the risks of climate change, embracing sustainable transportation needs to happen sooner than later, he added. "We simply can't afford to wait; we can't also afford to progress slowly," he said.