Click image for enlargement. Graphic by Mike Johnson.

Driving between Las Vegas and Los Angeles has never been a joy, even in the best of times. Soon, it's going to get a whole lot worse.

Hours-long traffic jams are expected to result from a series of new Interstate 15 restrictions around the Cajon Pass in Southern California that are tentatively scheduled to start in late September and continue through October.

The restrictions, announced Thursday, are to allow the renovation of I-15's interchange with Interstate 215 at Devore, Calif., and will involve weekend-long shutdowns of some freeway sections for the California Department of Transportation's so-called "Rapid Rehab" program.

Planners suggest that I-15 commuters avoid weekend driving, take long detours, fly or simply cancel their trips while work is under way.

"If it was me, I wouldn't go near the interchange during 'Rapid Rehab' weekends. I'd drive an extra 60 or 80 miles to waylay that," said Terri Kasinga, spokeswoman with CalTrans.

Officials in the Silver State hope advance notice of the disruptions will give motorists plenty of time to map their way around the work zone and save their trips.

"The best thing to do is plan before you take the trip," said Bob McKenzie, a spokesman with the Nevada Department of Transportation. "If they're aware of when or where the closures will be, they may not have to go through such drastic measures" such as flying or canceling a trip.

The closures are related to a $26 million plan to replace aging lanes of I-15 and I-215 and add a truck lane on northbound I-15 in that area. The project has already resulted in frequent weekday lane reductions on I-15 at the Cajon Pass.

Given the complex nature of the work, it's likely the schedule will change in some way in the coming weeks.

"The schedule we've released is tentative. It's subject to change. It's not in stone. This is what we are hoping to get done," Kasinga said. "We want to make it clear the schedule is fluid. It can change and it may change."

"Rapid Rehab" work is set to start the night of Sept. 29, with lane reductions on southbound I-15 at Devore. But traffic disruptions at that time are expected to be minimal, according to Kasinga.

The first big challenge for drivers will start the night of Oct. 6, when engineers will close southbound I-15 at the I-215 junction and northbound I-215 at its connector ramp with I-15 through Oct. 8. That will be followed by similar shutdowns of parts of I-15 or I-215 every weekend through month's end.

A detour will be posted, but authorities said it will only be there as a corridor of last resort for drivers who cannot avoid the Cajon Pass, and that drivers should avoid the area entirely during work times, if possible, or face gridlock conditions.

"They can expect substantial delays. It could be hours rather than minutes," Kasinga said. "It's all going to depend on diversions."

Planners hope as much as 40 percent of the cars and trucks that normally use I-15 at the Cajon Pass instead choose other routes or travel times.

Typically, I-15 carries more than 150,000 cars and trucks at that point each day, according to CalTrans statistics.

CalTrans is not recommending the use of any particular regional routes around the pass. "Instead of written alternate routes, we'll just show everybody what state routes are available" via Internet maps, Kasinga said.

Traditional alternates from southbound I-15 around Barstow, Calif., include a northern route via California state Route 58 to state Route 14 to Interstate 210 to Interstate 10 back to I-15 (which would add roughly 100 miles to the 270-mile drive), or a southern route taking California state Route 247 to state Route 62 to I-10 to I-15 or I-215 (which would add around 50 miles).

Similar closures can also be expected early next year, though dates are pending.

Authorities are urging travelers to keep tabs on the progress of work and to be attuned to changing plans, schedules or travel conditions.

TENTATIVE RESTRICTION SCHEDULE

Shown here are tentative dates, times and locations of planned road work-related restrictions at the junction of Interstate 15 and Interstate 215 in Devore, Calif., between Las Vegas and Los Angeles, from late September through October:

• Restrictions will start at 11 p.m. Friday, Sept. 29 with southbound I-15 lane reductions at Kenwood Avenue, where southbound ramps will also be closed. Those restrictions will be in place until Sunday Oct. 8.

There will be no posted detour for highway traffic, though there will be an alternate route marked for local ramp traffic.

• At 9 p.m. Friday, Oct. 6, engineers will close southbound I-15 at the I-215 junction and the link between northbound I-215 and northbound I-15 through 1 p.m. Sunday, Oct. 8. Substantial delays can be expected.

During that time, drivers will still be able to access I-215 from southbound I-15 and there will be a posted detour on Interstate 10 via I-15 and I-215.

• At 5 p.m. Friday, Oct. 13, the link between southbound I-15 and southbound I-215 will be closed through 1 p.m. Sunday, Oct. 15. Moderate delays can be expected.

Drivers will have a posted detour from southbound I-15 to Glen Helen Parkway to northbound I-15 to southbound I-215.

• At 11 p.m. Friday, Oct. 20, the connector between northbound I-215 and northbound I-15 will be closed until 1 p.m. Sunday, Oct. 22. Moderate delays can be expected.

A detour will be offered from northbound I-215 to Glen Helen Parkway to northbound I-15.

• At 8 a.m. Saturday, Oct. 28, northbound I-15 will be closed at the I-215 junction and northbound ramps at Kenwood Avenue will be closed through 4 a.m. Monday, Oct. 30. Substantial delays can be expected.

During that time, drivers can detour from northbound I-15 to southbound I-215 to Kendall Drive/Palm Avenue to northbound I-215 to northbound I-15.

• Authorities have yet to schedule a closure of the northbound I-15 connector to southbound I-215. That closure will likely take place during weeknights sometime this fall.

• Additional restrictions can be expected early next year. Dates, times and details are pending.