At least one traffic expert predicts that northbound I-5 will not see crippling traffic jams Monday morning (see maps below).

8:00 a.m. prediction:

People are well-informed and they will react to news about construction closures by avoiding the area, says Oliver Downs, principal scientist for Kirkland-based Inrix. The company produces real-time traffic updates, as well as predictions, for the Internet, cellphones and navigation devices. Its clients include trucking firms and other transportation-industry clients. Inrix's mathematical models take into account historical data about past accidents or incidents -- for instance, how motorists respond when Interstate 90 closes for a Blue Angels flyover.

The state Department of Transportation has speculated that I-5 backups could be 10 miles, 20 miles or longer.

"Our simulation isn't as pessimistic," says Downs, who forecasts that as of 8 a.m. Monday:

-- Traffic entering Seattle from the south will be only moderately worse than usual.
-- Highway 599 is "green" all the way to the First Avenue South Bridge -- a clue that "we'll see more avoiding than detouring," Downs says.
-- Interstate 405 will be stop-and-go through Renton, while Highway 520 is somewhat slower than normal, as people try to bypass the work area.

On Monday night, the Seattle Mariners' baseball game will increase congestion, of course, especially on Highway 99.

6:00 p.m. prediction:

But his forecast comes with one severe warning:

There could be a tenfold increase in blocking stalls or accidents, Downs says, because of narrow 10-foot lanes, visual distractions, "aggressive behavior," and a lack of shoulders. And the effects of a blocked lane would be magnified. He said the state knows this, so it is boosting State Patrol presence and incident-reponse trucks, and green screens will block driver views of the construction crews.

Inrix offers a standard, free 30-day trial of its "Inrix Traffic" for Windows mobile devices -- including traffic maps, speeds, and alerts ­-- at mobile.inrix.com.

Meanwhile, Seattle-based TrafficGauge is waiving some fees on its handheld map device, which shows congested areas as easy-to-read bold or flashing black lines; and it is offering free data for cellphones and personal computers.