VISIBILITY on roads is typically poor during and after an ashfall.
Reduced or zero visibility and total darkness resulted from the Taal Volcano eruption and the continuous ashfall has made driving conditions so bad. Vehicle headlights and brake lights have become ineffective, and barely visible to other drivers.
A road crash along the South Luzon Expressway is a good example of this situation. The truck driver did not see the road and ended up in a barrier tipping over the truck. Moreover, evern experience drivers find driving in the conditions left by the eruption difficult or impossible.
Vehicles whether fast or slow moving will stir up ash along roads and create billowing ash clouds. The bigger the vehicle the bigger the ash cloud behind it.
Rains mixed with ash will create a dangerous slippery surface. When ash on the road becomes wet, the mud-like is slippery sometimes with the same viscosity as oil. This can cause vehicles to lose traction and lose control of steering or braking.
But dry ash also causes roads to be slippery.
Road markings are also covered by ash deposits. In Agoncillo, Batangas for example, the ash on the roads reached about 2 to 3 inches thick. In Sta. Rosa, Laguna the mud already obscured road markings and along the Aguinaldo Highway heading down to Manila the markings that identify lanes, road shoulders, direction of travel are not visible. This has made drivers confused and disoriented with some parking in the middle of the roads as reported in the news.
Some safety strategies recommended by the Volcanic Ashfall Mitigation Center of the U.S. Geological Survey, Volcano Hazards Program before ash is manually or naturally removed from the roads are:
1) Close roads in highly-urban areas to facilitate clean up and prevent stirring up the ash.
2) Limit the number of vehicles allowed on highways; or space these by time, for example, to one vehicle every five minutes.
3) Impose short-term speed restrictions of 15-30 km per hour or less.
4) Advise motorists to travel only when really necessary.
4) Organize slow-moving convoys spaced at 1.6 km (1 mi) intervals.
The USGS also proposed that drainage and waste-water systems be protected from ashfall and need not be stressed by extracting ashfall is possible. Wet ashfall may also result in the clogging of roadside ditches and culverts.
During light rainfall the ashfall will cake or create slippery pools of mud. But poor or nonexistent drainage along a highway or road can cause erosion of the shoulder and road surface. During ash cleanup operations, ash should be prevented from accumulating in such drainages or entering underground wastewater or storm-drain systems.