The collision on Interstate 279 on that killed 13-month-old Judah Scrutchins during the sudden snowstorm Tuesday morning touched many, and some are asking how to stop future accidents like it.

The boy was in his safety seat, beside his twin sister and older brother, when the sport utility vehicle driven by his mother crossed the 44-foot grass median in Robinson during the squall. They crashed into a tractor-trailer coming the other way.

The truck driver was uninjured and all others in the SUV survived, though one passenger, Laura Kay Federoff, 34, was still in serious condition in the trauma unit of Allegheny General Hospital on Friday afternoon.

Would a barrier in the median have prevented the accident?

We can't know, and there are no plans to install median barriers on I-79, but the Pennsylvania Department of Transportation plans to begin installing steel cable in the medians on some suburban sections of Route 28, the Parkway North and Route 51 this year. They'll be the first of their kind in the Pittsburgh area.

At about one-third the cost of the more durable Jersey barriers known to every Western Pennsylvania driver, the high-tension cable barriers are now on more than 2,600 miles of highway medians in at least 25 states.

That's more than double what was in place only two years ago, according to the Texas Transportation Institute.

Nearly all the cable barriers are south of the Mason-Dixon Line or west of the Mississippi, and they cover only a fraction of the nearly 47,000 interstate miles in the 48 contiguous states. But expect more miles to be added each year because every study indicates these wire ropes save lives.

"Ninety-five percent of the time they are successful in capturing errant vehicles,'' Dean Alberson, assistant director of the Texas institute, said.

Picture a fence with four strings of thick, metal cable strung between the posts. As Todd Kravits, traffic engineer for PennDOT District 11, explained it, when a car hits the cables, the posts collapse but the cables restrain the car. He compared it to two people holding a bedsheet and having a third person run into it. There's some give, but it ultimately holds.

Mr. Alberson put it more succinctly: "Cars generally get kind of ensnared in the system.''

These won't work everywhere. The ground must be relatively flat and the median at least 16 feet wide because there can be eight feet of "give'' when the car hits cables. The Texas Transportation Institute recommends 24 feet, but Mr. Kravits says the medians are much wider than that on the stretches of I-279 and Route 28 where the fencing is planned.

Those stretches are between Exits 13 and 14, Creighton and Tarentum, on Route 28, and between the Camp Horne and Mt. Nebo Road exits on the Parkway North. The stretch of Route 51 south of the city, between Route 48 and the Westmoreland County line, has a median of only 18 or 20 feet, Mr. Kravits said, but the goal there is to stop motorists from making left-hand turns to businesses across the road.

These sites were selected because the data on crossover accidents suggested they are must vulnerable, he said. "We had no flags on any sections of [Interstate] 79.''

No barrier system can provide full protection. If the median isn't flat enough, the car can go right over the top of strung cables. And if a big vehicle is going fast enough, cables won't stop it.

On Feb. 13 last year, Interstate 5 in Washington state shut down when an SUV shot across the grassy median and struck a charter bus. The 64-year-old SUV driver died at the scene, having broken through two rows of median cable barriers.

After a state investigation, a concrete barrier to supplement cable barrier was recommended for that dangerous stretch of I-5. But the Washington State Department of Transportation noted "a new risk to northbound drivers who may hit the concrete barrier or may be hit by a northbound vehicle that ricochets off of the concrete barrier.''

According to that July 2007 report, the 10 mile-stretch of I-5 was the only place on roughly 135 miles of Washington freeways with cable median barriers that recorded any crossover fatalities.

These barriers also minimize damage to the vehicle and the riders because of the "give,'' and the cost of repair is kept low. It amounts to "a couple of people going out, reinstalling posts and clipping cable back to it,'' Mr. Kravits said.

For some drivers, it can't come soon enough. For others, it will come too late.