Moonwalkers are show attachments with motorized wheels - like Heelys that you see kids wearing around. But these are for adults and according to the company behind moonwalkers - they boast that it can increase the wearer's walking speeds by 250%. I have lived in Princeton and worked in New York City for over a decade and something like this would be a game changer. They are compact and can be simply worn on your shoes without having to handle other heavy gear and bother fellow commuters.
They attach to a wide variety of shoes using adjustable straps and magnetic buckles - so need to change what you wear. The devices continuously communicate with each other and monitor the user's gait to adjust speed. They can switch between Shift and Lock modes with a simple foot movement. A video from the Moonwalkers' Kickstarter project is available in the article.