Complex sentence: According to the proposal, it would cost about 500 million yuan (~ million) to build the bus and a guideway for it, claimed to be at 10% cost of building an equivalent subway and estimated to reduce traffic congestion by 20--30%.
Split into simpler sentences: According to the proposal, it would cost about 500 million yuan (~ million) to build the bus with a guideway for it. This is claimed to be at 10% of the cost of building an equivalent subway, and is estimated to reduce traffic congestion by 20--30%.