Highway engineers know that freeway ramps can be risky for many kinds of vehicles, a point driven home on Sunday when a gasoline tanker rolled over and ignited an inferno that destroyed a major Bay Area highway node.
Flames from 8,600 gallons of spilled gasoline leaped into the steel underbelly of another freeway ramp above it, melting girders and causing it to collapse on the roadway below.
One miracle in this crash was that nobody died. The other extraordinary outcome was the amount of damage -- tens of millions of dollars to the roadway and probably much more in lost commuting time for tens of thousands of Bay Area residents.
"It is a human problem," acknowledges John L. Conley, president of the National Tank Truck Carriers Assn., the group that represents the estimated 30,000 trucks that haul gasoline, chemicals and other liquids on public roads coast to coast.
The human problem is particularly at issue on freeway ramps, including both exit ramps and transition roads that take traffic from one freeway to another freeway.
Many drivers routinely scoff at the advisory speed limits on these roads, which are posted on yellow signs. They are not formal speed limits, which are posted on black and white signs. In general, a driver cannot be cited for violating an advisory speed limit. (One caveat is that police can always write tickets for failure to drive at a "safe and prudent" speed.)
Perhaps for this reason, many drivers go far in excess of the advisory limits. I have received any number of e-mails through the years from drivers who say these limits are set far too low. If you look on the Internet, many self-proclaimed geniuses assert that only "stupid highway engineers" come up with these limits.
The accident Sunday may help foster some proper respect for the issues highway engineers grapple with in setting these limits.
The speed advisories on freeway ramps and most highway curves are set for a worst-case scenario, a wet roadway at night, a top-heavy vehicle that can easily roll over or a sharp enough curve that limits a motorist's line of sight, said Sean Skehan, principal transportation engineer for Los Angeles.
"There is one sign for everybody that uses a ramp," Skehan said.
The geometric design of these ramps and the speed posting are derived from the bible of highway engineers, known as the Manual on Uniform Traffic Control Devices, published by a technical association but endorsed by the federal government.
California has its own edition of the manual and specifically assigns more conservative speed limits on ramps, Skehan said.
"It doesn't matter how we post it," Skehan added. "If you don't follow it, drivers will skid off the road."
Accident investigators for the California Highway Patrol say it is too early to know what caused driver James Mosqueda, 51, to veer into the concrete wall of the ramp.
The California Department of Motor Vehicles said Mosqueda has a valid and properly endorsed license to drive a gasoline tanker. The Associated Press reported Tuesday that Mosqueda had previous criminal convictions for drug possession and burglary.
The ramp, which takes traffic from westbound Interstate 80 to Interstate 880, has an advisory speed of 50 mph. Any number of issues could have caused the accident: excessive speed, driver fatigue, equipment failure, driver distraction or something else. Perhaps the speed advisory was set too high.
The trucking company, Sabek Transportation in San Francisco, is part of CHP's biannual safety inspection program and has earned the highest rating each year since 1996, said CHP Chief Steve Vaughn.
Nonetheless, another Sabek gasoline tanker rolled over on June 23, 2006, on a ramp going from Interstate 780 to Interstate 80 in the Bay Area, Vaughn said.
A CHP investigation faulted excessive speed, even though the truck was estimated to be going only 20 mph in a zone posted at 25 mph. Here's an example of even very low speeds on a ramp not being cautious enough.
Lots of gasoline tankers crash and burn every year. But nobody knows exactly how many, according to the American Trucking Assn.
The American Trucking Assn. recognizes the need to improve truck safety. It has asked the Federal Motor Carrier Safety Administration to create a rule that would put electronic governors on all new trucks that limit their maximum speed to 68 miles per hour.
Why the government has to be petitioned for such a safety rule by the industry itself is at best puzzling. The association is also asking for stronger rules on training for new drivers.
Conway, the tanker association chief, said many tanker companies already tell drivers to go 10 mph below the advisory posted on highway ramps. Their vehicles have centers of gravity that clearly affect the risk of a rollover.