When I-5 gets closed for repairs, will gridlock rule?

Sacramento commuters and traffic officials face perhaps the most worrisome and uncertain summer ever.

What's going to happen when state highway officials post "closed for repair" signs on busy Interstate 5 in downtown Sacramento next month?

Will there be freeway chaos regionwide? Will gridlock rule downtown streets?

Or will drivers adapt – take a train, a bike or a back road – and manage to flow smoothly through the June and July construction period?

State Department of Transportation officials are hopeful but unsure. They've never closed a core Sacramento freeway before for repairs.

"We're on pins and needles," Caltrans spokesman Mark Dinger said. "Your guess is as good as ours."

Although the series of closures starts on May 30 – a Friday night – the real test will come Monday, June 2, when tens of thousands of commuters return to work downtown.

They will find I-5 northbound closed in downtown as crews begin the two-month process of digging up and replacing the decayed and leaking roadway.

The northbound lanes will get two closures this summer. Southbound lanes downtown separately will experience two closure periods.

Dinger said it could well get ugly, illustrated by this unsettling scenario:

If you live in Elk Grove and need to get to the Sacramento airport during that first Monday morning commute, your 17-mile drive may be a two-hour nightmare.

With northbound I-5 closed, airport-bound drivers will have to trail-blaze a new route, possibly joining hordes of truckers detouring onto West Sacramento freeways, or braving the often-clogged Capital City Freeway.

Downtown commuters, meanwhile, are likely to shift to other freeways or surface streets.

The result, Caltrans engineers say, will be a ripple effect of congestion throughout the metropolitan area.

Caltrans' computer simulations suggest freeway drivers could experience two to three times normal congestion.

Two sections of freeway are likely to be especially hard-hit.

Interstate 80, coming toward downtown from Davis and West Sacramento, could be trouble. It is designated as a truck detour route during the closure. Every additional truck is equal to three or four more cars on the road.

Officials also warn drivers to steer clear of southbound I-5 in Natomas during the weeks those lanes are closed in downtown.

Drivers will be able to reach downtown on I-5 those weeks, but traffic will be funneled into two lanes and forced to take the Richards Boulevard and J Street offramps. That means backups as far north as Natomas.

Those are what Caltrans calls "worst-case" scenarios – what happens if drivers don't change routes during the closures.

Officials believe that if they can get the word out well enough, the traffic maze may not be nearly as bad as many fear.

The agency is spending $270,000 to alert drivers, and there's precedent for optimism.

When Caltrans closed the San Francisco-Oakland Bay Bridge over Labor Day weekend last year, other bridges had heavy traffic, but it wasn't nearly as bad as officials had feared.

"It was stellar," said Beth Ruyak of C.C. Myers, the Rancho Cordova company that did the Bay Bridge work and will patch I-5. "We were thrilled with how the public responded."

Caltrans spent a half-million dollars on an outreach campaign before and during that closure.

When a gas tanker truck crash and fire destroyed an Oakland freeway connector last spring, officials predicted major traffic jams. Almost none occurred as bus and train ridership jumped and carpooling increased.

Similar, surprising traffic flows happened during construction work on a damaged I-5 tunnel near Santa Clarita last year.

Caltrans says it has learned that even though some people might miss the early warnings, drivers will adapt.

"Those first couple of days could be bad," Caltrans local traffic operations official Jim Calkins said. "But when people learn where they are going, congestion (may be) a fraction of what we're projecting."

Data show that on a typical day, 190,000 vehicles use I-5 downtown. Half of them, however, are not going into downtown. Caltrans expects many of those just passing through will steer clear of the city center.

Warning signs are posted as far north as Redding and south as Tracy, and also on Interstate 80 in the Bay Area.

Truckers by now have alternate-route maps.

Caltrans has a Web site, www.fixi-5.com, that shows closure schedules and detour maps, and offers e-mail alerts.

And by project start day, Caltrans officials say, they will have sent out 130,000 informational mailers.

The Sacramento Transportation Management Association and other agencies are publicizing a van and carpool Web site – www.sacramento-tma.org – as part of a push to "Beat the Creep" in the coming weeks.

Officials expect the worst freeway crowding in the morning, but downtown streets leading to freeways are also afternoon choke points.

City of Sacramento officials say hot spots may include P Street at the onramp to southbound I-5, Highway 160, and major boulevards – such as Riverside, Stockton, Freeport and Folsom – into and out of downtown.

Officials will tweak intersections to give drivers longer green lights and put personnel with flags at troublesome sites. They also may temporarily repaint turn lanes at some intersections.

Sacramento International Airport officials say they are getting the word out to workers and car rental agencies.

Ross Harper of El Dorado Hills, who flies often, says he's got the message loud and clear – Watch out for I-5! – but that doesn't answer his basic question:

What route will get him to the airport, and how long will it take?

"I'll get out the map and talk with some neighbors," he said. "Maybe they'll know."

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• Call The Bee's Tony Bizjak, (916) 321-1059.