Jerusalem's central Jaffa Road artery is a building site these days - reduced to barely two lanes as the infrastructure is laid for the much-anticipated light-rail system. Tractors and bulldozers routinely ply the route past Jerusalem Capital Studios toward the Mahane Yehuda open-air market. But the driver who maneuvered his massive yellow Caterpillar tractor along that same stretch of road at noon on Wednesday had devastation, not construction, on his mind. According to a young, bearded eyewitness, pale and shaking in one of the cafes that line the street, the driver ploughed down the road, crushing cars indiscriminately and flipped an Egged bus onto its right-hand side, in a swathe of destruction two hundred or more meters long. Initially, it was suggested that the driver, soon identified as an east Jerusalem resident employed by a local construction firm, might have lost control of his vehicle and accidentally caused the bloodshed and chaos. But Yoni Ben-Menachem, the Israeli Radio chief who was in his car when the tractor sped toward him, quickly laid that theory to rest, recounting that he had made eye contact with the driver, who was calm, focused and knew exactly what he was doing. Ben-Menachem swerved onto the sidewalk to safety. Minutes after the driver was finally shot dead by security officials after a struggle in the tractor's cab, Jaffa Road had become a combined building site and terror-attack-zone. From the second, third and higher floors of the television studio buildings overlooking the terror route, camera crews filmed the ambulances converging, the victims being stretchered away, and the police gradually sealing off the long, long path of wreckage. Several cars lay turned on their sides, or smashed. Helicopters clattered overhead. A uniformed woman with a bomb-detector dog on a leash walked along the lowered light-rail route alongside the road, checking that no explosive devices had been planted to coincide with the attack. A mother, her head covered in a floral scarf, appealed frantically to a policewoman to let her through because her daughter was shopping in Mahane Yehuda. Ambulances wailed in the distance, struggling to get through the halted traffic clogging the surrounding streets. And hundreds of onlookers, many of them young yeshiva students in white shirts and black kippot, thronged behind the police tape. The security barrier has dramatically reduced the incidence of attacks inside Israel by West Bank Palestinians in recent years. But three months ago, in the last major terror attack in the capital, an east Jerusalem resident killed eight students in a nighttime attack at the Mercaz Harav Yeshiva. On Wednesday, Jerusalem's vulnerability to attacks from "within" - by a perpetrator with the residency rights to move freely around the city - was murderously demonstrated.