I'm all for gentle, safe, and efficient driving, but if you'd like to cut emissions of CO2, driving less is the best way to go. I can't see the inputs to the infographic, so I'm using EPA's figure of 8887g of CO2/gallon of fuel*, which, assuming fuel economy of 25 miles per gallon, comes to 735lb of CO2 emitted per thousand miles driven. Those leadfoots in Philadelphia, are doing about 7% worse than that. To put it another way, even Philadelphians could make up (carbon and fuel-use-wise) for their bad habits by cutting 75 miles out of every 1000. Biking, walking, public transport, or carpool also reduces traffic and the inefficient slow-and-go driving that results, and increasing the demand for these (currently) alternative modes sends a message to cities and their policy makers to improve these options.
For the driving one does do, combining trips is a good strategy. In the U.S., you can usually get groceries and greeting cards in the same shopping center, so there's no need to drive all over in search of multiple items. Just thinking ahead and getting all you need, to avoid an extra grocery trip, is a good start. It'll save mileage as well as cold starts, which is when a particularly large proportion of the unburned hydrocarbons and NOx are produced. Cold starts are hard on cars, too, so the easiest, shortest trips to walk or bike are the most important ones to avoid in a car.
Combining trips saves time, too.