On Thursday February 19th, the MTA re-timed six traffic signals from 16th to 21st, a pilot for a few weeks that will enable the agency to gauge the real-world impacts of reduced speeds on traffic flow.
The main goal is to improve vehicle flow and calm traffic to prevent energy intensive starting and stopping. The slower synchronized timing will also likely prove to be a great convenience to cyclists along the route .
Motorists are already seeing a benefit. Initial studies show the re-timed signals improve overall travel time by more than a minute during peak commute hours. Additionally, motorists will save gas and reduce pollution if they drive at a steady 15 mph pace.
In 2002, Portland, Oregon implemented a citywide traffic signal optimization project ,
which saves motorists over 1,750,000 gallons of gas and 15,460 tons of
CO2 each year. It cost $533,000, paid for by the Climate Trust of Oregon  carbon offset program. The majority of streets in downtown Portland are timed at 12-15 mph for pedestrian safety and optimal traffic flow.
In Amsterdam , both trams and buses save time from signal re-timing. On average trams move 1.5 minutes faster and buses 3 minutes faster.
This is expected to benefit pedestrians as well. Studies show  the severity of pedestrian injuries in crashes with cars increases exponentially with only slight increases in vehicle speed. Pedestrians face a 5 percent chance of dying when hit by a vehicle traveling 20 mph, though that figure jumps to 45 percent for a vehicle going 30 mph and 85 percent at 40 mph.
Flickr Photo: pbo31