Can current cities be redesigned for a future of healthier citizens?

Cities are dense life centers offering a greater range of opportunities and services than those typically present in rural settings. While this offers a strong draw to people looking to take advantage of the wealth and income cities offer, organic growth of urban areas can decrease efficiency and home values when the settings become too complex and disorganized to remain inviting. Urban decay then leads to increases in crime and can be connected with shifts towards suburban settings, which in turn increase air pollution. It's a complex problem that has largely been met with middling results. Can new trends in urban planning help reclaim urban zones?The World Health Organization forecasts that 60% of humans will live in a city by 2030 and the number will rise to 70% by 2050. Bigger, higher, denser - the characteristics of cities around the world involve a lot of words ending with '-er' - such as dirtier as air pollution increases along the population curve.But much science fiction presents a clean landscape full of healthy happy people. Is this really possible? Recent research claims New York City will offer longer life expectancies to children born in 2009 than the national average (2.5 year difference of 80.6 for NYers vs 78.2 for the rest of the country). An article I recall (but can't find) says Parisiens were just behind NYC - the key difference being New Yorkers are often in a hurry and take faster and longer steps.Having lived in Toronto for 5 years, I can speak to life in a large and very navigable city: it's a mixed bag. On one hand, we could take a right on Yonge Street and walk miles to the waterfront only stopping at crosswalks. On the other hand, the air was dirty and there are a loooot of crosswalks to hold you up. Going a few blocks can result in several street corner waits while cars take their turn at the light. Not a bad thing during nice weather, but pretty frustrating and chilly in the dead of winter.Nick Stockton at Wired covers the science of space syntax and the company Space Syntax and their work to help revitalize urban areas by identifying new city design to smooth out foot traffic in dense cities from the UK to China. It's an interesting look at how a company can change the navigability of a city based on existing foot and vehicle traffic to identify how changes to existing routes, down to the addition of single stairs, could make improvements - or make things worse.The part that surprised me was the use of sun-path models to improve the attraction of foot-paths. I'm guessing this goes both ways, having both enjoyed the shade of a building on a hot day and dreading the extra chill on a cold day. If pulling all of this data together can make cities cleaner, safer, increase real estate value and help us live longer, then a future of beautiful cityscapes is a possibility.But I wonder: would you be okay with your city, regardless of size, spending tax money to improve walkability?