Yesterday, we were contacted by Joe Vazquez, a KPIX/CBS 5 reporter seeking some data on a potential slowdown on the West Bound lanes of the SF Bay Bridge in the recent days/weeks. Using some of the analytic capabilities of the BeatTheTraffic.com system, we were happy to help the best we could.

Here is the content of our message to Joe:

“For the Bay Bridge Westbound, from the Cantilever Section through Treasure Island Rd, (so this would include the new S curve section) I have some average speed of traffic data from the Beat the Traffic(R) system (note that we have multiple sources but in this area it is mostly from the 511 system)

For comparison purposes, I have graphed the same day of week:

• Monday August 3
• Monday August 31
• Monday September 14
• Monday October 12 (Columbus Day)
• Monday November 16

The data indicates that the average speed of Morning commute is getting increasingly worse, except for Monday October 12 of course, which was Columbus day and a special case.

Morning commutes drop from 39 mph or so on August 3 to:
- Monday August 31: 29 mph (this also corresponds to back to school increase in traffic)
- Monday Sept 12: 24 mph
- Monday Nov 16: 13 mph.

So it seems your intuition might be correct and there is a downward trend of travel speeds on the Bay Bridge in that section, which affects the entire travel time.

I am not aware there were adverse weather conditions on either day that could explain slowdowns,
but perhaps this should be checked. Tuesday October 13 was a very bad storm, but that is another story”

See the graphs below:

The following graphs plot the average speed of traffic as reported by 511.org on the West Bound Bay Bridge (I-80) between the Cantilever section and Treasure Island Rd. The Y axis denotes the speed of vehicles in miles per hour and the x axis the time of day, starting from 00:00 all the way to 23:59. The speed is typically at free flow speeds during the night and drops during rush hours. We are looking at the speed drops and what is the lowest measured speed during the morning rush hours.

Monday September 14

Monday October 12 (Columbus Day)

Monday November 16