FLEXIBLE BARRIERS OFFER ALTERNATIVE TO HIGH COST OF WIDENING FREEWAYS.

Byline: Ernest E. Pund Riverside Press-Enterprise

Imagine a huge zipper down the middle of Highway 91 through Corona, opening lanes as needed for the morning and evening rush.

Sounds incredible, but it is already happening elsewhere. ``Zippers,'' as they've been nicknamed, are used on the Coronado Bridge over San Diego Bay, on Interstate 30 headed into Dallas and on freeways in Massachusetts and New Zealand. The first ones appeared about 11 years ago on the East Coast.

The zipper is made up of one or two flexible, concrete medians alongside the permanently fixed median. A machine the size of a motor home shifts the median from side-to-side, alternately opening the middle lanes for the heaviest direction of traffic.

Highway 91 between Interstate 15 and Highway 71 may be a good candidate for a zipper, according to a Riverside County Transportation Commission report.

``It's much, much less expensive than widening a highway. There's no doubt about that,'' said Bill Lake, western regional manager of Barrier Systems Inc., the Nevada-based company that holds the patents and builds the systems.

The cost of widening Highway 91 by one lane in each direction has been estimated by local transportation officials at about $14 million a mile.

By contrast, installing the zipper for 2.1 miles over the Coronado Bridge ran about $2 million, a state Department of Transportation official said. The 4.5-mile stretch outside Dallas cost about $8 million.

``We call it the zipper, because it kind of looks like a zipper,'' said Sharon Reiter, spokeswoman for the Texas Department of Transportation.

Zippers differ from highway to highway. The Dallas freeway is eight lanes wide. Down the middle is a permanent barrier. On either side is a flexible barrier.

For midday traffic, the flexible barriers sit snug alongside the permanent barrier, providing four lanes in each direction.

For the evening commute, one of the flexible barriers is shifted, providing four regular lanes and an enclosed car pool lane for homebound commuters. The barriers are reversed for the morning commute.

A shoulder within the enclosed lane allows for emergencies, which so far have included births of at least two babies, Reiter said. ``I think it definitely warrants a serious look,'' said Alex Clifford, chairman of the Riverside County Transportation Commission and a Riverside city councilman. There may be other sections of the freeway in the county where the cost of building new lanes would make a zipper an inexpensive alternative.

Barrier Systems officials said they knew of no accidents involving the machine, which typically rests at either end in an enclosed garage where maintenance is done.

Each segment of the concrete barrier is 32 inches high, more than 3 feet long and weighs about 1,500 pounds. The sections are connected by steel hinges.

The top of the barrier is shaped in a ``T.'' As the machine rolls along the median, a series of small, angled wheels lift the barrier from the underside of the ``T'' and shift it the width of the lane.

The machine is steered automatically by a guidance system that follows a cable embedded in the highway. The machine can move about a mile of barrier in 20 minutes.