So what's holding it back? In Maryland, the biggest obstacle to any strengthening of drunk driving laws has generally been the House Judiciary Committee and its chairman, Del. Joseph F. Vallario Jr. of Prince George's County, a criminal defense attorney. But the state has made progress in expanding use of ignition interlocks over the last half-decade despite that impediment, most recently by adding the "minor child in the car" provision last year. The result has been a steady increase in the use of the devices (up 38 percent to 11,101 participants in the program in fiscal 2014 compared to 8,049 four years earlier) and a corresponding decline in traffic fatalities.