The accident that landed bicyclist Susanne Kibler-Hacker in the hospital is still under investigation, but the Concord police must, at the earliest opportunity, explain what happened and why no charges were filed.

Kibler-Hacker, a Society for the Protection of New Hampshire Forests vice president, is a highly experienced cyclist and coordinator of the state's ride-to-work days. She was wearing a helmet and reflective vest when she was struck from behind by an as-yet unnamed Weare woman while bicycling on Clinton Street west of Silk Farm Road.

The details of the accident, to the extent they have been determined, have not been made public. This much is clear: The lanes at that point are 11 feet wide, not counting a narrow 12- to 18-inch paved shoulder. The speed limit is 45 mph and visibility is good. The accident occurred in front of the home of Lindsay Goff, a nurse who assisted the victim, who was thrown some 20 feet by her bike's impact with the car.

A police spokesman said speed and alcohol were not a factor in the accident, and the motorist was let off with a warning to "exercise due care." Kibler-Hacker's injuries were serious enough that she was taken to Dartmouth-Hitchcock Medical Center. If a warning is indeed is the only charge levied, the police need to explain why.

Unless a cyclist on the side of the road swerves to the left suddenly to avoid an obstacle, leaving a passing motorist no time to react, a driver who hits someone from behind is almost inevitably at fault. Most roads are only wide enough to be safely shared by bicyclists and motorists when everyone is paying attention and minding the rules. The widespread use of cell phones, iPods and laptop computers in cars, when added to the risk presented by drunk drivers, radio knob twiddlers, dropped cigarettes, dripping sandwiches and screaming children, have made cycling much more dangerous.

Have cell phone records been checked to see if the driver was distracted or could something else have caused her to fail to avoid the collision? Bicycles and motor vehicles have an equal right to share most roads. But no matter who makes the mistake, when an accident occurs it's the bicyclist who loses.

When speeds are slow and a lane constricted by construction or a parked vehicle, a bicyclist can, with caution, legally claim the center of the road to become more visible and slow traffic until it's safe to return to the roadside. Doing so is neither safe nor smart when speeds are high, and it seems unlikely that Kibler-Hacker would have done so.

A new law went into effect this year that requires that motorists allow at least 3 feet between their vehicle and a cyclist when passing.at 30 mph or less and an additional foot of clearance for every 10 miles per hour in excess of that. That means the Weare motorist should have passed no closer than 4 feet from Kibler-Hacker.

For economic, environmental and health reasons, bicycling should be encouraged through the creation of wider roads, well-marked bike lanes and, yes, law enforcement. Bicyclists and motorists are both charged with obeying traffic laws but there are scofflaws in both camps. Unless a charge is levied in this case, the police must explain why they feel that a mere warning to the driver is enough.