<P> The emission rate for cars using highways has been on a decline between 1975 and 1995 due to regulations and the introduction of unleaded petrol . This trend is especially notable since there has been a growth in vehicles and vehicle miles traveled by automobiles using these highways . </P> <P> A consistent shift from land based trade to sea based trade has been recorded since the last three millennia . The strategic advantages of port cities as trading centers are many: they are both less dependent on vital connections and less vulnerable to blockages . Oceanic ports can help forge trading relationships with other parts of the world easily . </P> <P> Modern maritime trade routes - sometimes in the form of artificial canals like the Suez Canal - had visible impact on the economic and political standing of nations . The opening of the Suez Canal altered British interactions with the colonies of the British Empire as the dynamics of transportation, trade and communication had now changed drastically . Other waterways, like the Panama Canal played an important role in the histories of many nations . Inland water transportation remained significantly important even as the advent of railroads and automobiles resulted in a steady decline of canals . Inland water transport is still used for the transportation of bulk commodities e.g. grains, coal, and ore . </P> <P> Waterway commerce was historically important to Europe, particularly to Russia . According to the Encyclopædia Britannica (2002): "Russia has been a significant beneficiary . Not only have inland waterways opened vast areas of its interior to development, but Moscow - linked to the White, Baltic, Black, Caspian, and Azov seas by canals and rivers - has become a major inland port ." </P>

What impact have the panama and suez canals had on bypassing barriers and trade
find me the text answering this question