Air pollution is becoming more and more of an issue all over the world, prompting several automakers to develop greener vehicles with fewer carbon emissions. With cities like London, which recently violated the European Union's (EU) air pollution guidelines by having 36 "bad air" days this year when the EU only allows 35, it's no wonder auto companies like Toyota are creating environmentally-friendly vehicles like the plug-in Prius (which in recent tests was able to travel 62 miles per gallon).

Toyota's plug-in Prius achieves 13 miles of all-electric range and additional mileage from the hybrid system. According to the Inside Line team, it will be sold at a base price of $27,550, which is a $4,000 premium the company's original Prius. 

While the plug-in Prius has several advantages, it also has a few points against it. For instance, achieving 62 mpg isn't really a huge feat for the plug-in since the traditional Prius is able to reach this through hypermiling. Also, the plug-in owner would have to drive 215,100 miles to make up for the additional cost to start, and when the price charging is included, it will likely cost more to own a plug-in version of the Prius because of it's dependency on the cost of electricity. 

Despite a few downfalls, Inside Line agrees that the plug-in Prius is "one of the best hybrids available." Vehicles like these could certainly help situations like London's, where the EU is coming down on them for air pollution problems that have overstepped certain guidelines. 

Monitoring equipment in London recorded the city's 36th "bad air" day after finding dangerous levels of minute airborne particles. According to EU guidelines, the city is only allowed to have 35 of these "bad air" days and London is now the worst polluted city in Europe.

"This latest breach is yet another wake-up call for the mayor of London and the government," said Sarah Ludford, London Liberal Democrat MEP. "Research has shown that airborne pollution in London could be responsible for up to thousands of premature deaths a year; this is an invisible public health emergency."

The consequences of violating these guidelines are hefty fines and several court cases. London's government has requested an exemption from air quality guidelines until 2011 in hopes of repairing the problem, especially in time for the 2012 Olympics. 

"Air pollution is bad for our health," said Janez Potocnik, European Commissioner. "It reduces human life expectancy by more than eight months on average and by more than two years in the most polluted cities and regions."

The EU is growing tired with London's lack of contribution to bettering city air quality, as the city has neglected to follow the guidelines since 2005. In addition, several critics have protested London's ability to receive any more exemptions or extensions, hoping it will press the city to take action.