Earlier this week, a new law went into effect in California: drivers must now give bikers three feet of space when passing, or pay a fine.

Should cars have to give bikers three feet of space when passing?

On its face, this sounds like a great policy for bikers. But there are some bike advocates out there who actually think the benefits of these "three-foot" laws — now on the books in 24 states — are overblown.

These advocates point to a general lack of enforcement of the rules — but they also argue, more broadly, that making slight concessions for cyclists as part of a system designed entirely for cars is no way to make city biking safe and accessible to the casual rider.

This disagreement is part of a broader disagreement amongst cyclists: whether bikers should simply share the road with cars, obeying all of the same rules (a philosophy commonly called "vehicular cycling"), or whether cities should be investing in specialized infrastructure so that bikes and cars don't have to mingle (a position often called "segregated cycling"). This is a guide to that surprisingly contentious debate.

"Same road, same rules"

The first position, vehicular cycling, is simple: Bikes should have the right to share the road with cars, and in exchange, they should have to follow all the same rules.

Under this system, bikers would have to do lots of things that many casual bikers don't always currently do — always ride in the direction of traffic, always use hand signals, always come to a full stop at all stop signs and red lights, and ride in the center of the lane whenever possible. Ideally, bikes should travel at a pretty fast clip, and bikers should look over their shoulder when changing lanes or turning to make sure they don't cut anyone off.

The ideas behind vehicular cycling can be traced back to a California bicycling engineer named John Forester, who wrote a remarkably influential 1976 book called Effective Cycling. One of Forester's oft-invoked mantras was: "cyclists fare best when they act and are treated as drivers of vehicles."

When Forester developed his view, US cities had very few bikers — and virtually no bike lanes. If someone wanted to ride a bike for transportation, the only option was to use the roads that had been built for cars, where drivers weren't used to sharing.

The way for bikers to coexist safely with drivers was to behave the same way that cars did — following all rules in a predictable manner. What's more, it was actually dangerous for bikers to hug the right side of the lane, because that could lead to cars trying to squeeze by at uncomfortably close distances. Instead, Forester argued, bikers should ride in their center of the lanes, forcing cars to use the opposite passing lane to pass.

Forester also battled against the notion of "cyclist inferiority": the perception, held by both drivers and bikers themselves, that they didn't belong on the roads. Some places even had laws requiring bikes to remain on the sidewalk. Riding confidently and consistently in the center of the lane, where legal, would show they had the same legitimate right as anyone else, and could be counted on to follow traffic rules.

This school of thought holds that some slight rule changes — like, say, California's three-foot law — can help make biking safer, but on the whole, bikes are vehicles that are perfectly capable of sharing roads with cars.

Further, many proponents of vehicular cycling are actually against measures like protected bike lanes and separated trails. One reason, they argue, is that these lanes are more dangerous at intersections than just riding in the road — because cars turning in front of these lanes don't expect bikes to ride through.

Other vehicular cycling proponents also see these lanes as a tool for segregating cyclists and kicking them off roads. Building bike paths, they say, is a precursor to keeping bikes off regular roads altogether — much like the way pedestrians are confined to sidewalks.

The argument against treating bikes like cars

More recently, lots of bike advocates have taken a different position: that bikes are indeed different than cars, and the whole "vehicular cycling" idea is a relic of the days when biking was a fringe, hardcore activity.

Now that there are lots of bikers, these advocates of segregated cycling argue, we should focus on constructing bike-specific facilities, like protected lanes and paths, rather than retrofitting a car-centric road system to cram in a few bikes. The goal, in essence, should be making sure that cars and bikes don't have to share the road any more often than is necessary.

The logic here is that roads were designed specifically with cars in mind. As a result, putting bikes on them is inherently risky, and the number of people who will brave a busy thoroughfare and claim a lane amidst speeding cars is relatively small.

Martha Roskowski of the People For Bikes organization recently came up with a nice analogy for this idea: riding in the streets, like a car, is akin to skiing a black diamond run down a mountain. There might be a minority of bikers who'll do it (and even enjoy it), but to make most people comfortable with the idea of biking in a city, we need the equivalent of green circle and blue square ski routes — protected lanes and trails. More importantly, these need to make up a linked, cohesive system, so people can bike from home to work, for instance, without needing to brave a black diamond.

Most people in the segregated cycling camp agree that bikes should act more or less like cars when they do have to bike on streets. But a minority argue not all of the same laws should necessarily apply.

I took this position when I argued that bikes should be allowed to roll through stop signs, and ride through red lights after coming to a complete stop (as is legal in Idaho). The basic reason is that stop signs and traffic lights were designed with cars in mind, and bikes are not cars.

With stop signs, that means that a biker doesn't need to come to a complete stop to give him or herself enough time to assess the safety of proceeding through an intersection, because he or she moves more slowly than cars in the first place. Additionally, many stop lights are triggered to change colors based on sensors buried in the road that detect cars, but not bikes.

So who's right?

As with many debates, neither side here is entirely right or wrong, and there's a lot of overlap in the actual goals sought by people in both groups. But on the whole, as the popularity of cycling has grown, most biking advocates have gradually moved out of the vehicular cycling camp.

There are a few different reasons for that. One is the success of places that invested in bike-specific infrastructure. The world's cities with the highest rates of bicycling — such as Copenhagen and Amsterdam — have the highest amounts of protected bike lanes and trails, and research shows this correlation also holds for US cities.

most biking advocates have moved out of the vehicular cycling camp

It's often hard to parse cause and effect, but survey data indicates that people started biking because bike lanes were built — not the reverse. A survey of bike commuters in Washington, DC, for instance, found that they were willing to travel up to 20 extra minutes if it'd mean taking a safer off-street trail, rather than riding in the street. A recent study of six American cities with newly built protected bike lanes, meanwhile, found that 25 percent of bikers decided to bike more often because of the lanes in particular.

There's also lots of raw data showing that biking in protected lanes or paths is simply safer than riding on the roads. A review of 23 different studies on biking safety found that bike-specific lanes, on the whole, are the safest place for bikes to ride.

A pair of recent Canadian studies looked at injury rates and cyclists' preferences for 14 different infrastructure options — including normal streets, cycle tracks (that is, protected bike lanes), non-protected bike lanes (those protected by a line of paint, but not a physical barrier), and multiuse paths (i.e. combined walking and biking paths). The results were unequivocal: a cycle track was by far the safest route, cutting injuries by 90 percent compared to a major street with no bike lane.

And while three-foot laws like California's new one are great, there's some evidence that, at least in some places, a lack of awareness and enforcement means they're less than perfectly effective. Maryland passed a similar law in 2010, and a study conducted a year later found that about 17 percent of cars still gave bikers less than three feet of space when passing.

Ultimately, it seems that the era of vehicular biking has come and gone. In much of the United States, biking is getting ever more popular, and many cities are increasingly investing in infrastructure to promote it. It does not look like the future of biking is sharing the road.