The sheer number of miles is staggering. In Washington, national-forest roads have grown from about 9,000 miles in 1960 to 22,000 miles today. Northwest is accessible to four-wheelers than to salmon. As was made painfully clear during the recent floods, forest roads magnify the effect of heavy rains. Meanwhile, rainfall both adds weight to the soil and lubricates its movement.
Water rolls off roads into culverts, focusing the flow which adds even more to erosion.
New road construction techniques are having some success in mitigating negative effects, although these improvements may be canceled out as roads are built into increasingly steep and fragile areas to get at remaining timber. Moreover, new techniques don't take care of the legacy of existing roads built to outdated specifications. Declining budgets for road maintenance makes the problem worse. According to the Oregonian , Forest Service spokeswoman Gail Aschenbrenner estimates the current budget is half of what's required. Without adequate funding to clear culverts and ditches and correct other problems, the Forest Service is unable to prevent slides and washouts in heavy rains.