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On a crisp, wispy autumn morning, I am hurtling down a winding Rock Creek Park horse trail on a mountain bike, eyes locked on the next 20 feet of my life. I hop barriers, absorb rocks, blast through rotting logs, swerve around bugaboos—everything necessary to avoid the shrieking pain of a high-speed wipeout. Like many others, I find the park a sanctuary, where one can pump legs and lungs, stroll, or guide a horse through a slice of peace and quiet in the middle of a mad city.

But my harmony is not free: Take a walk through the park, look into the eyes of trail users of every ilk, and you will see something: We bikers appear skulky, as if we just walked out of an alley after a dope purchase and everyone around knows it went down.

That look is not deceiving. Mountain biking on Rock Creek Park’s unpaved trails is illegal, and most bikers know it. But on workdays and busy weekends, when I lack the time for a pilgrimage to legal biking grounds, Rock Creek offers the perfect little workout in clean forest air. Steep short ups, tight curvy downs, and flood-plain flats make the lawbreaking tempting enough. The fact that I never get caught—and the knowledge that my sport erodes the trails no more than hiking and equestrianism—make my riding almost worry-free. Almost.

While U.S. Park Police officers are easily eluded, frequent bikers of Rock Creek Park are lucky if they have not encountered one of a growing number of peeved hikers and equestrians who claim the two-wheelers have made park trails an increasingly dangerous place to relax.

“We tell bikers, “I’m riding an animal that weighs half a ton with a brain the size of a walnut,’ ” says one horsewoman. “A scared horse is extremely unpredictable.”

For hikers the risk is equally stark—metal on flesh. “I’ve seen guys come screaming around a corner worrying about where they are going—trying to avoid rocks and stuff—and they barely miss hitting us,” says one middle-aged woman. “It can be pretty scary.”

Aside from baseball umpires, few go to the park expecting an argument. But during the past 10 years, mountain bikers riding Rock Creek Park’s dirt and rock trails have encountered hostile hikers and horse-borne travelers. Mountain-bike opponents say the cyclists are spooking horses, endangering hikers, hastening erosion in the park, and breaking the law.

OK, we are criminals—just like the mayor-elect. Rock Creek Stables barn manager Alex Williams complains that bikers often crowd horses when trying to pass.

“I have seen many bikers who stop, dismount, and let horses by—if everyone did that, it would probably be OK,” Williams says. “It seems a lot of bikers know they shouldn’t be there. They are the polite ones.”

About 60 horses are kept at the Rock Creek Stables; upward of 100 horses hit the trails on clear weekend days, and that can be a prescription for disaster.

Al Finger, a local mountain-bike racer who has ridden Rock Creek, knows firsthand the dangers of suddenly encountering a horse on a trail. While biking a trail at about 25 mph in California, he ran into one.

“The horse owner was pretty cool about the whole thing…and the ranger was cool,” he says. But Finger was tagged with a $250 ticket. “I also damaged a $3,500 bike,” Finger recalls. Neither horse nor equestrian were hurt.

Ken Serrbee is the rare worker in Rock Creek Park who can recall a horseman being thrown in an encounter with a bikeman. “The injury risk is potentially high if bike use goes up,” says Serrbee, a resource management specialist at the Rock Creek maintenance yard. “We have been lucky.”

National Park Service (NPS) Rule 4.30 has long banned the riding of bicycles on all trails except specially designated ones, and violators can be fined $50. In 1989, the NPS began posting circle-and-slash signs explicitly banning mountain bikes from trails in Rock Creek Park and Glover-Archbold Park, and today the markers can be found on 90 percent of NPS trails in the District.

Few formal complaints have been filed against bikers, but as tempers grow short between the sporting classes, a blowup may be in the offing: The park trails are just too appetizing for bikers to ignore.

“For short, challenging rides, these trails are perfect,” says one 28-year-old biker who does not want to be named. “The civilians bitching at you can’t catch you. And third, I think the cops have better things to do,” he says. “I’ve probably ridden in here 200 times and I have never run into a ranger.”

“We get a lot of [phone] complaints, especially from the Glover Park area, from the Potomac Appalachian Trail Club,” says Lt. Henry Berberich of the Rock Creek Park Police substation. But most cops give bikers only warnings. “I have not issued any tickets,” he comments, “but if we get a lot of complaints about an area and find repeat offenders, we will ticket.” Still, horsemen file many more complaints about unleashed dogs than they do about bikers, he says.

(The Potomac Appalachian Trail Club, which helps maintain some of Rock Creek Park’s paths, refused to comment on the biker controversy because it doesn’t talk to the press on “political issues.”)

NPS spokesman Earl Kittleman acknowledges that bikers have a good theoretical case for access to the park: “Other interests get their land—the golf course, horse stables, and trails and commuter roads, so the question has to come up.” Of the 43 miles of unpaved trails in Rock Creek Park, equestrians can ride on 13 miles of trail. The remaining paths are reserved for hiking.

Some jurisdictions plan their parks so two-wheelers can share trail space with bipeds and four-leggers, says Tim Blumenthal, executive director of the International Mountain Bicycling Association (IMBA). The city of San Jose, Calif., cut its park trails a little wider than most hiking paths to increase sight lines, and at Fairmount Park in Philadelphia, more than 15 miles of trails are open to biking, he adds. Fairmount isn’t problem-free—reckless, fast riders endanger other trailsmen, and the blazing of unmarked trails in the park has been a chronic problem. Even so, the sharing concept has worked in Philly.

Blumenthal says Rock Creek Park should designate a few loops in the more remote areas for bike use, marked and maintained by mountain-bike clubs. Such trails could be closed in wet months such as February and March to prevent path damage, he adds.

As a Rock Creek rider, I keep these rules in the front of my mind: When you see a horse, get off the bike, lay it down to the side of the trail, and step aside until the animal is gone; keep your speed manageable when you cannot see more than 50 feet ahead; and maintain a cheerful demeanor because, after all, you are the outlaw. If bikers behave around horses and avoid surprising people, more park users may favor licit mountain biking.

Williams, for one, would embrace a bike/equestrian compromise.

“There is a whole string of trails between Meadowbrook and Rock Creek Stables that are less used and could be open to bikers—maybe with a sign posted that horse riding is at one’s own risk,” she says, but she is a minority among horsepeople. “Most would prefer to see no bikes.”

One argument against trail sharing, she says, is the high percentage of inexperienced horseback riders who can’t control a scared animal.

One would expect erosion to be the albatross of the mountain biker, the one inescapable bane that would trump all other issues and confirm that biking destroys. But the authorities are not so sure.

“People say biking causes erosion, but it is beyond that,” says stables manager Williams. “The trails already are in real bad shape.”

“Do not fall into the trap of those who say nature is delicate,” Kittleman warned. “The grass will grow back.” The problem posed by mountain biking, he says, is “use trends.” One rider cuts a path, then another, and pretty soon there is an inappropriate path that might cause erosion.

When Rock Creek Park’s trails were designed in the ’30s and ’40s, ecologically sound routes were not plotted, says Serrbee. “People, bikes, horses—it doesn’t matter. The damage is there.” When bikers ride around water bars—the railroad ties placed in the center of a trail to sluice water down the hillside—to avoid the bump, they create a new path for water to follow, exacerbating the erosion.

Walter Wells of the Sierra Club says Rock Creek Park’s most erosion-prone areas include the Valley Trail north of Military Road (under rehabilitation now), the Ridge Trail in that same area, and Glover Park between Cathedral and Massachusetts Avenues.

Trying to assess the erosion risk “is like asking, “How bad is fire?’ ” says Will Murray, director of the conservation program for the Nature Conservancy in Boulder, Colo. Heavy use can blow out a trail, but where few people ride, there may be no problem. “There likely are thousands of mountain bikers in the D.C. metro area, with limited off-pavement options. Concentrating them in any park will greatly speed erosion,” Blumenthal says. I would guess regular mountain bikers in Rock Creek Park number in the hundreds, but that figure is debatable.

“If you have a steep, erodible hill and people are carving the same path down it over and over—following the fall line and braking a lot—you will have bad erosion,” Murray says. “That creates a water route which requires human intervention; it will not fix itself. But on a dry forest floor covered with leaves, you might never know [bikers] were there.”

There is a dearth of scientifically valid data comparing trail damage from biking, hiking, and horseback riding, but Blumenthal says the primary cause of erosion is the creation of the trail itself.

“By doing that you have altered the land,” he notes.

Trails are most vulnerable in the spring, when the ground is the softest, Blumenthal adds. Maintenance is essential to correcting erosion, as is the rerouting of trails.

Serrbee, who performs trail maintenance in Rock Creek Park about two times per month from spring until fall, reports minimal foot-related damage and only moderate bike-caused damage. Horse impact is heavier, but not drastic, because horse trails are designed to handle the pressure.

Blumenthal contends that 95 percent of those complaining about erosion are merely looking for environmental justification for their point of view. But many bikers check their common sense at the trailhead, and a lot of tension is bikers’ fault. In urban-area parks such as Rock Creek, the most important thing for bikers to remember is to yield the trail. Under IMBA’s code, equestrians have right of way over all other trail users; and bikers should yield to hikers as well.

Cooperative solutions are possible if land users are willing to work together to maintain their sanctuaries, Blumenthal and other bike advocates say. “All nonmotorized trail users have much more in common than they do apart,” Blumenthal maintains.

In Southern California, mountain bikers contribute by helping park authorities widen tracks, clean up weeds, and pick up litter, the 22-year-old Finger says. “One problem is hikers think bikers are out to destroy, and that is not true,” he adds. “You get one guy not making room [for a hiker] and the whole opinion [of bikers] goes down.” The root of conflict, he says, is simple contact: If the park separated areas for each use and the various sportspeople did not see each other, there would be fewer complaints.

Mountain biking in Rock Creek Park may yet be legitimized. “The park needs to look at current uses and maybe make changes. If we can change for the better without great expense, such changes are possible,” Lt. Berberich says. “Something may come up next week that would require us to rethink the rules.” Serious discussions have been held regarding more off-road recreational use but, Berberich remarks, “I don’t think it will happen. It would involve major spending [in the form of] a topographical study, an engineering study, and liability concerns.”

Asked how biking might be allowed, Kittleman replies, “I do not know what we’d get into. Maybe we could set up a course.”