What does it take to get charged with manslaughter when your negligent driving kills someone? Last year the driver of a semi entered a bike lane and killed a Chicago bicyclist. He was issued tickets for driving in a bike lane and failure to take due care with a bicyclist. Why mere tickets instead of a more serious charge? —Alan G. Thomas

Accidents happen, and when they do the person enclosed in a big metal box has a pretty clear advantage over anyone walking around or rolling by on non-motorized wheels. Our laws mostly acknowledge this imbalance—drivers are supposed to be extra careful not to run anyone down—but we’re still reluctant to criminalize auto-inflicted deaths. As with most criminal matters, prosecutors have the discretion to choose how to proceed, and they’re not only constrained by the laws on the books but discouraged by their odds in the courtroom.

With bicyclists on the streets in ever greater numbers—as of 2012, bike commuting was up by 60 percent over the decade prior—incidents like the one you cite (involving the 20-year-old rider Lisa Kuivinen) have predictably become more common. There are now more than 700 bicycle deaths in the U.S. annually and upward of 40,000 injuries, nearly a third of which involve cars—more than any other single factor. The stats for what happens to the party at fault after these collisions are trickier to track. One look at the D.C. region found that less than half of at-fault drivers were prosecuted. In New York City, which sees 10 to 20 cycling deaths each year, motor vehicles caused more than 14,000 pedestrian and cyclist injuries in 2012, but only 101 citations were issued for careless driving. Surely reckless bike behavior was a factor in some cases, but by any estimate, prosecution rates are certainly low, requiring the injured (or the family of the deceased) to bring private criminal complaints or pursue civil suits.

And that’s baked into the system. As a society—one that drives too much, many would argue—we’ve made choices about allocating the risk that ensues when people get behind the wheel. Our traffic laws are basically designed on the assumption that collisions occur even when drivers exercise a reasonable amount of care. Unless one driver clearly hasn’t done this, the state generally opts not to pursue a criminal conviction, leaving the parties to duke it out in court themselves. And gauging negligence—legally, the failure to take reasonable care—is a slippery matter. Just as driving laws vary by state, so too do definitions of negligence (thanks a bunch, federalism). This isn’t a law school torts lecture, though, so let’s just say there are differing degrees of it, and at the tippy top is criminal negligence, what you’d have to show to support a charge of vehicular homicide.

Since negligence is tough to demonstrate to a jury, prosecution becomes way likelier when the driver’s behavior is notably egregious. A DUI is the gold standard here, but a hit-and-run incident also helps a struck cyclist’s chances at obtaining a guilty verdict. Hit a biker while committing some obvious traffic infraction, like running a red light, or violating a new distracted-driving law, and a prosecutor’s likely to come after you. So for many cycling-safety advocates the idea is to make more laws, bike-specific or no, and so create more ways to establish that a driver was negligent.

There have always been some laws looking out for non-drivers in the roadway. Due-care statutes protected even the least attentive farmer’s wagon from being sideswiped by a shiny new Essex or Packard on an unlit country lane. And drivers have long been required to maintain a “safe distance” when passing bicyclists, but just try and make a case in court based on that vague standard. More recent state laws have set a minimum passing distance of three feet, though this functions mainly as a deterrent—it’d take an eagle-eyed officer indeed to notice if you’d given a biker only two feet and eleven inches. In 2007 Oregon passed a “vulnerable user” law, modeled after a Dutch regulation, and eight states have followed suit: these laws increase penalties when a driver strikes anyone who’s not in a car—pedestrians, cyclists, skateboarders, et al.—typically setting a minimum fine around $1,000.

But norms govern our everyday behavior far more than laws do—it’s hardly the fear of being locked away that keeps most of us from becoming cat burglars or hit men. Legislation alone won’t deter drivers from driving aggressively around bikes, or even guarantee enforcement, much less prosecution—a common complaint among cycling activists is that the legal system, from cops and DAs to judges and juries, identifies too readily with drivers. Advocates thus try to gently nudge the debate in their direction, using the term “bike crash” rather than “bike accident” to imply the cause is driver error rather than mere chance. Meanwhile, recent research suggests that the biggest boost to bike safety might simply be more bike use: a 2014 Colorado study found that per-rider crash rates were lower at intersections with heavier bike traffic. The more often drivers have to share the road, seemingly, the better they get at not running everyone else off it. —Cecil Adams