Eight multilateral development banks announced at the Rio+20 summit here Wednesday that they would set aside $175 billion to finance sustainable transport systems over the next decade. The pledge was made jointly by the World Bank, Asian Development Bank, African Development Bank, Inter-American Development Bank, CAF-Development Bank of Latin America, European Bank for Reconstruction and Development, European Investment Bank and Islamic Development Bank. Transport is one of the fastest-growing source of greenhouse gases, driven especially by urban growth in giant emerging economies. Around one billion people are likely to move to cities over the next 20 years, which means traffic congestion, air pollution and road accidents will become major urban challenges. The voluntary commitments were made at the start of a three-day summit in Rio de Janeiro to cap the UN Conference on Sustainable Development. The gathering marks 20 years since the 1992 Earth Summit placed climate change, desertification and species loss on the world\'s political agenda.