The vibrations from sections of rough road on the Bay Bridge intended to slow motorists before the deadly S-curve are prompting concerns that the speed deterrents could lead to damage on the aging span.
Previous failures on key structural pieces of the heavily commuted bridge, resulting in its shutdown, have been blamed on vibrations from vehicle traffic and wind.
But now, concerns have been raised that the rumble strips on the westbound span are causing vibrations that are rattling support beams that have already needed emergency repairs.
Following a spate of S-curve accidents — including a fatal incident in which a truck traveling at an alleged 50 mph flipped over the railing — Caltrans last year added new safety features. They include raised strips roughly three-eighths of an inch tall that create vibrations that drivers feel when traveling over them.
“We put the rumble strips out there primarily to gain motorists’ attention,” Caltrans spokesman Bart Ney said. He said the agency, which oversees the bridge, wanted motorists to be alert and slow down before the curve.
However, tenured UC Berkeley engineering professor Abolhassan Astaneh-Asl said vibrations from the rumble strips could damage the bridge, including its eyebars, which are steel support beams manufactured in the 1930s. Eyebars are outdated technology not used in new bridges.
Heavy trucks passing over the rumble strips pose the greatest danger, he said.
“This is like jackhammering the bridge continuously,” Astaneh-Asl said. “There is no reason to do this.”
The bridge was shut down longer than scheduled last year after a cracked eyebar was discovered. A forensic analysis later found that decades of road- and wind-based vibrations caused a thin ridge to split, which grew quickly into a large crack.
The cracked eyebar was initially reinforced with an improvised steel device that later fell onto traffic. Caltrans also blamed vibrations for that failure. The damaged section of eyebar was eventually replaced.
Ney said the rumble strips cause “absolutely minimal” vibrations and said they do not pose any danger.
“Most of the vibration is in the rubber of your vehicle,” Ney said.
The vibrations can upset motorists driving light vehicles.
“If you’re going slow, it just rips your car apart,” said Larry Tubelle, who commutes from Moraga to San Francisco in a 2010 Toyota Prius. “My car was quiet and smooth, and now it’s got rattles all over the place.”
The Bay Bridge links Oakland to San Francisco.
300,000 Vehicles crossing the Bay Bridge daily
52 Bridges in California that contain eyebars
1,680 Eyebars on Bay Bridge’s eastern span
1.5 inches Width of crack discovered in Bay Bridge eastern span eyebar last year
8 Eyebar inspections planned every two years on Bay Bridge’s eastern span
1 Eyebar inspection planned every two years on other Caltrans bridges
$35 million Repair costs related to last year’s eyebar crack
$3 million Tolls lost due to bridge closures last year
Sources: Caltrans, California Legislature