FOR COMMUTERS in Northern Virginia, the arterial paralysis that struck traffic Wednesday was an exasperating taste of how monumentally messed up this region's routinely overburdened road system can suddenly become. It was an unlikely convergence of events that produced the dawn-to-dusk standstills. Further, the mess pointed up how vulnerable greater Washington could become to even more calamitous jams.

The truck crash raises pressing questions about the transport of explosives along the roads and how well prepared regional authorities are to respond quickly and decisively.

Any truck loaded with 17 tons of highly explosive powder and barreling along high-speed freeways and onto tricky ramps is an alarming prospect -- but not in itself an uncommon occurrence. Some 5.5 billion pounds of explosives are used in the United States each year, according to industry estimates, much of the load transported by truck. No state or federal regulations prohibit this transport or restrict the times of day or night that these loads may be on the roads. Virginia does have some limitations on amounts and types of hazardous materials that can be run through tunnels or along certain local streets.

But are officials ever alerted as to when such materials are coming through? Or how long the driver has been at the wheel? Or the last time the rig underwent serious safety checks? In Wednesday's incident, it took trained officials hours of consulting and calling to figure out how best to approach the cleanup. These delays were somewhat understandable, given the complicating factors: a driver charged with reckless driving, a rig flipping off the side of a ramp at the most treacherous interchange in the region, a site of constantly heavy traffic and a threat of lightning.

Still, regional, state and federal officials ought to examine every aspect of this scene, which in a flash could have turned into a true disaster.