Thick traffic crawls slowly along Mission Boulevard in Fremont’s Mission San Jose area most weekday afternoons, as thousands of people make their way home from work and school.

The commute was especially nightmarish on Aug. 3 when a dump truck carrying gravel rolled over as it turned right from the Interstate 680 south off-ramp onto Mission Boulevard north, crushing part of a sedan and spilling its load across the roadway.

Similar big rig rollover accidents have happened at that same interchange a total of five times since Dec. 2015, according to city officials. It’s a dangerous trend that’s caused severe gridlock and ruined the commute for thousands in an area where brake lights and long queues have become the norm.

“My immediate reaction is like, jeez, this is deja vu here,” Hans Larsen, Fremont’s director of public works said in a recent interview about the latest accident. Others on Facebook posted similar comments about the incidents.

“This happened to a different gravel truck only a few months ago at that same location. Maybe they need to work on the intersection to make it safer,” Heather Wallace wrote in the comments of a Fremont Police Department post about the latest incident.

On Aug. 31 2017, an almost identical accident occurred in the same spot during the afternoon commute.

A rig carrying tons of dirt overturned on the road as it turned right off the highway ramp, landing in the median and flinging one of its trailers across southbound lanes where it smashed into a fence, snarling traffic.

“It seems like trucks plow down that 680 offramp too fast, too often,” Glenn Gutierrez wrote in a Facebook comment on the police department’s post about that incident. “Can it be made safer?”

“We’re very concerned about it,” Larsen said of the phenomena. “It’s something that warrants significant study.”

In the recent accident, two people were injured, and ramps and lanes were closed for hours in the area, heavily delaying traffic.

It’s become so alarming that the city is holding a special meeting Sept. 5 with the California Department of Transportation (Caltrans) which manages the highway, the off-ramp and Mission Boulevard, to discuss the interchange.

“It’s to just ensure that they’re aware that there’s a pattern of trucks overturning at this location and try and understand what kind of response and reaction they may provide to that,” Larsen said.

Eric Sauer, a spokesman for the California Trucking Association said he’s happy to hear Fremont and Caltrans officials are meeting to discuss this issue.

“We’ll have to wait and see what comes out of those meetings, and hopefully we can be part of those discussions,” he said.

Adding more signs, rumble strips, and “making sure that drivers do understand that…you need to take it slow” is something the association fully supports, Sauer said.

But reminders of the toll these rigs have taken on Mission Boulevard are quite evident. The road is gouged along the curve and near the median where trucks have sliced into the pavement as they toppled over, and there are oil stains from engines in prior accidents.

Gravel, dirt and debris from trucks and cars, including glass and lug nut covers are visible in the median along Mission near the ramp.

Experts who’ve studied rollovers say drivers of large trucks carrying loads may not be able to adequately reduce their speed when exiting the highway in order to make the sharp right turn safely.

In the lead up to the off-ramp, vehicles travel on a downhill stretch of 680, and the ramp itself is also steadily sloped downward.

Drivers continuing straight or turning left onto Mission Boulevard must stop at a signal at the bottom of the ramp, but those turning right onto Mission have a dedicated merge lane and are not required to stop.

Larsen said the current setup encourages vehicles to make turns at higher speeds than may be safe, especially for commercial trucks with a high center of gravity.

“There isn’t really any reason to stop or slow down unless you see a pedestrian crossing there,” he said of the turn.

There’s also the issue of signage. While there has been a suggested speed limit sign of 30 mph posted just before the ramp for years, Caltrans said there were no signs warning drivers about the downhill slope of the ramp until recently.

Three days after the latest wreck, Caltrans installed two new yellow “hill warning” signs just before and at the beginning of the ramp. They show an 8% figure and an image of a truck headed downhill.

Federal guidelines from the Manual on Uniform Traffic Control Devices for Streets and Highways say those signs should be installed in advance of any downgrades of eight percent that are more than 750 feet long, which the Mission off-ramp is, and “where crash experience and field observations indicate a need.”

Near the bottom of the ramp, a yellow sign recently installed shows a right turn arrow and suggests a 15 mph limit for the curve, but Caltrans officials couldn’t say if that sign had been posted there previously. The sign is not visible in some Google Maps images as far back as 2015.

However, warning drivers, especially truckers, to reduce speed near the bottom of the ramp might not be effective, according to Xiao-Yun Lu, a senior researcher at UC Berkeley’s Institute of Transportation Studies and an expert in vehicle dynamics control.

“Some drivers believe that their truck can stop if necessary. But once they get on the curve, that would be too late,” Lu said in an interview.

“If some drivers do not act earlier, they cannot reduce the speed,” he said, especially with a heavy load. “If the load is not perfectly distributed, this overturn is more likely to happen.”

A report about commercial vehicle safety Lu co-authored with other researchers in 2007 said speed is an important factor for truck safety.

“High speed not only causes threats to other vehicles, but also causes instability” of the truck itself, such as a rollover,” according to the report. It also noted that “a loaded tractor-trailer requires 20-40 percent further stopping distance than a car. This situation is worsened with downgrades and wet pavement.”

Lu said that while road engineers would need to closely study the ramp and turn before making changes, some simple solutions could be implemented quickly.

He said that while the curve of the turn is slightly banked at its outer edge, steeper banking may be needed to help trucks negotiate the turn safely.

Further reducing the suggested speed of the off-ramp to 25 mph, and placing more signs in advance along the highway to warn drivers about the need to reduce speed could also help, he said.

Larsen agreed, and said police reports have indicated one of the primary reasons for most of the rollovers “has been the inability of heavily loaded trucks to adequately brake and slow down because of the downgrade.” He added in an email that in two of the crashes the left front tire of the truck buckled at the turn “causing the truck to topple over.”

Larsen added that the congested area of Mission Boulevard has been “on our radar screen for upgrades” for other reasons, including the danger posed to pedestrians and bicyclists crossing the street where the curve is located.

Larsen said redesigning the bottom of the ramp so it’s safer for all would be a good start.

“I think we’ve seen enough problems happening here.”