Smoke and Highway Safety

Smoke can cause highway safety problems when it impedes a drivers ability to see the roadway and can result in loss of life and in property damage at smoke levels that are far below NAAQS. This section focuses on highway safety issues in the Southeastern United States because this is where the foremost forestry-related air quality problem has been in the past. We also describe tools being developed to aid the land manager in avoiding highway safety problems.

Although smoke at times can become a problem anywhere in the country, it is in the Southern States, from Virginia to Texas and from the Ohio River southward, where highway safety is most at risk from prescribed fire smoke, principally because of the amount of burning done in the South and the proximity of wildlands to population centers. Roughly 4 million acres of Southern forests are treated with prescribed fire each year (Wade and Lunsford 1988). This area is by far the largest acreage subjected to prescribed fire in the country. Prescribed fire treatment intervals, especially in Southern pine (in an area extending roughly from Virginia to Texas), is every 3 to 5 years. These forests are intermixed with homes, small towns, and scattered villages within an enormous wildland/urban interface. During the daytime, smoke becomes a problem when it drifts into these areas of human habitation. At night, smoke can become entrapped near the ground and, in combination with fog, creates visibility reductions that cause roadway accidents. The potential exists for frequent and severe smoke intrusions onto the public roads and highways from both prescribed and wildland fires.

Magnitude of the Problem

Smoke and smoke/fog obstructions of visibility on Southeastern United States highways cause numerous accidents with loss of life and personal injuries every year. Several attempts to compile records of smoke-implicated highway accidents have been made. For the 10 years from 1979 through 1988, Mobley (1989) reported 28 fatalities, over 60 serious injuries, numerous minor injuries, and millions of dollars in lawsuits. During 2000, smoke from wildfires drifting across Interstate 10 caused at least 10 fatalities, five in Florida and five in Mississippi.

As the population growth in the South continues, more people will likely be adversely impacted by smoke on the highways. Unless methods are found to adequately protect public safety on the highways, there exists the prospect that increasingly restrictive regulations will curtail the use of prescribed fire or that fire as a management tool may be altogether prohibited.

Measures to Improve Highway Safety

Several approaches are being taken to reduce the uncertainty of predicting smoke movement over roadways:

High-resolution weather prediction models promise to provide increased accuracy in predictions of wind speeds and directions and mixing heights at time and spatial scales useful for land managers. The Florida Division of Forestry (FDOF) is a leader in the use of high resolution modeling for forestry applications in the South (Brenner and others 2001). Because much of Florida is located within 20 miles of a coastline, accurate predictions of sea/land breezes and associated changes in temperature, wind direction, atmospheric stability, and mixing height are critical to the success of the FDOF. High-resolution modeling consortia are also being established by the USDA Forest Service to serve clients with interests as diverse as fire weather, air quality, ecology, and meteorology. These centers involve scientists in development of new products and in technology transfer to bring the products to consortia members.

Several smoke models are in operation or are being developed to predict smoke movement over Southern landscapes. VSMOKE (Lavdas 1996), a Gaussian plume model that assumes level terrain and unchanging winds, predicts smoke movement and concentration during daytime. VSMOKE has been made part of the FDOF fire and smoke prediction system. It is a screening model that aids land managers in assessing where smoke might impact sensitive targets as part of planning for prescribed burns. PB-Piedmont (Achtemeier 2001) is a wind and smoke model designed to simulate smoke movement near the ground under entrapment conditions at night. The smoke plume is simulated as an ensemble of particles that are transported by local winds over complex terrain characteristic of the shallow (30 to 50 m) interlocking ridge/valley systems typical of the Piedmont of the South. Two sister models are planned -- one that will simulate near-ground smoke movement near coastal areas influenced by sea/land circulations, and the other for the Appalachian Mountains.