GHAZNI, Afghanistan—Throughout Afghanistan, roadside bombs are increasing not only in number but also in size, with devastating consequences for U.S. troops and beleaguered Afghan truck drivers alike.

Culverts that run under the road to help drain and irrigate surrounding fields in the rural country now regularly conceal these powerful improvised explosive devices, or IEDs, with increasingly large charges. Roadside bombs that once weighed 10 to 20 pounds have morphed into multigallon drums packed with 200 to 500 pounds of explosives, which insurgents roll into culverts with wheelbarrows.

The enhanced bombs have in some cases proved effective in destroying the U.S. military's expensive new Mine Resistant Ambush Protected vehicles—the product of a multibillion dollar investment by the Pentagon that features a V-shaped hull to absorb and disperse the impact of roadside bombs.

The vehicles were not built, however, to withstand 200-pounds worth of explosives. "They've flipped MRAPs 15 feet in the air sometimes," says one U.S. officer in Afghanistan. "And they break them in half." U.S. troops inside the overturned vehicles have been crushed and seriously injured by falling equipment.

The Taliban's latest IED offensive has turned Highway 1, the paved artery that links Kabul to Kandahar, from a once powerful symbol of progress in Afghanistan into a deadly stretch littered with burned-out bridges and smoldering trucks.

The new bombs, which U.S. military officials say began cropping up in June, are part of an insurgent effort, they add, to disrupt commerce, create chaos, and strike at the heart of government efforts to bring progress to strategic provinces like Ghazni. Highway 1 runs through the province, which remains home to a number of Taliban leaders.

The construction-grade explosives are trucked in from Quetta, a Taliban stronghold in neighboring Pakistan, according to U.S. intelligence officials. But the material is manufactured elsewhere, leading officials to believe that insurgents are bypassing border crossings in eastern Afghanistan, where U.S. troops have a greater presence, to bring them in through southern provinces. U.S. troop presence is sparse to nonexistent in the south of the country. The 24th Marine Expeditionary Unit returned from violent Helmand province in early October, and for now, U.S. troops are stretched too thin, say Pentagon officials, to replace the marines.

On one recent drive between U.S. military installations in Ghazni province, troops from the 1st Battalion of the 506th Infantry Regiment dismounted to check each culvert along a paved road pocked with craters and blown-out bridges. It is painstaking and time-consuming work—the culverts are every 100 meters apart in some areas. Insurgents "are targeting the infrastructure, because that's what the government can provide," says Capt. Spencer Wallace, a company commander with the battalion.

But recently the battalion caught a high-tech intelligence break when an unmanned aerial vehicle discovered a nine-man team planting IEDs near a U.S. forward operating base and called in an air strike. When troops got to the scene, they found bodies with watches set to Pakistan time and pockets full of Pakistani money.

It was, they surmised, a cell sent to train Afghan insurgents to build and plant large roadside bombs. With the help of intelligence streams from more UAVs, the battalion was able to track down five IED-planting teams in seven nights, leading to a decrease in roadside bombs in the area. Overall, those kinds of attacks have decreased from 30 a month in July and August to some five a month in September and October.

But the ongoing concern, says one U.S. military official, is that there simply are not enough unmanned drones to go around, and the prospect of U.S. troops checking every culvert they cross is unrealistic. "We need more consistent [UAV] surveillance," says the official. "Because these guys will regroup and come back."

