Soon, after checking under the hood and kicking the tires, we will be scanning our car’s on-board diagnostic system (OBD). Sanjay Sarma has been investigating ways to take advantage of a car’s sensor bus, the module that records and conveys information about the vehicle’s components and systems. Sarma hopes to make the OBD increasingly useful and essential to consumers concerned about their fuel consumption and carbon footprint. Car companies have been “cagey” and even “opaque” about the information bus that now comes standard in most cars, but auto enthusiasts have long known how to tap into this system for information on a car’s vitals. Sarma, a mechanical engineer comfortable tinkering with car systems, wondered if he could devise a way to gather a continuous stream of data on fuel consumption from OBD, and then come up with accessible and informative metrics for the data. As the internal combustion engine figures less in the future of cars, and batteries and electric motors more, says Sarma, “logging in and learning from this data will be a bigger and bigger deal.” With a small team of researchers, Sarma conducted hundreds of miles of driving tests in urban and highway settings, micrologging vehicle fuel consumption. They first analyzed the effects of traffic congestion, which demonstrated that traveling slowly did not diminish fuel consumption, because in real life, accelerating and braking frequently wastes energy. They figured out a sampling rate ideal for harvesting an adequate stream of information and avoiding a sea of data, and a way of separating idling time from moving time fuel consumption. Ultimately, Sarma’s team came up with “simple kinematic measures” for “flogging” (fuel logging) that could apply to cars of all stripes — high-performance gas guzzlers, or the latest battery-powered inventions. Sarma is enthusiastic about the possibility of using cell phones as an interface with a car’s OBD. With GPS and accelerometers, cellphones could re...