Caltrans has received numerous emails and phone calls regarding the one-inch thick steel plates that have been placed on the upper deck of the Bay Bridge just west of the Yerba Buena Tunnel. Although the plates have been designed to accommodate 50 mile- per-hour traffic, many drivers slow down prior to the plates. The slowing of just a few vehicles on a congested bridge can greatly increase traffic congestion. Many motorists have complained about the increased delays.
Hoping to reduce the number of vehicles slowing down in front of the plates, Caltrans has beveled the edges of the plates. Now traffic hits the plates at a 45 degree angle, rather than a 90 degree angle. This has had some beneficial effect, but it has been hard to gauge its effect on the reduction of traffic congestion.
What purpose do the steel plates on the bridge serve?
The steel plates are covering gaps on the bridge where Caltrans has removed bridge expansion joints. The expansion joints allow the bridge to expand and contract according to the ambient temperature. Decades of traffic traveling over the expansion joints have caused them to deteriorate.
How long will the plates be on the bridge?
Caltrans is repairing 19 of 75 joints on the upper deck of the suspension span of the Bay Bridge. It will take six months and cost $ 2 million to complete this task.
Why must the bridge joints be repaired?
The joints occupy the area between two large rectangular concrete slabs. The corners of the slabs are covered with steel to prevent them from eroding under the daily impact of thousands of tires. Even the steel cannot protect the concrete indefinitely. Eventually, the concrete around the joint begins to chip, crack and spawl. Thatís the condition that we find in 19 of the expansion joints.
Can you use a thinner plate?
No, the plates need to be one-inch thick to endure the battering they take from high volumes of car and truck traffic.
Can the plates be place lower into the bridge deck?
The roadway has only a small layer of concrete on top of the steel bridge structure. Therefore the plates cannot be inset in the bridge.
Can you paint the plates?
Apparently, there is study that indicates that painting the plates a color similar to the roadway can be helpful. Apparently, if the color of the plate blend with the roadway, the psychological effect of driving over a big plate is diminished. Basically, itís too late for that. Everyone knows where the plates are located and we do little good by camouflaging them. Also, the plates are textured to prevent skidding. The friction of the tires on a textured plate would rub off the paint in no time.
Iíve seen these plates on other bridges. Why are they causing so much traffic congestion here?
Traffic on the Bay Bridge is extremely heavy. Approximately 280,000 trips are made across the bridge daily. Because traffic is so tightly packed on the bridge, the affects of small incidences are greatly magnified. It only takes a small percentage of motorists slowing down to produce wave of slowing vehicle, the ripple effect of traffic congestion across the bridge. While there are steel plates on other bridges, congestion levels are only slightly increased by slowing traffic because of the lower volume of vehicles.