Caltrans Uses iCONEs to Monitor Traffic During Bay Bridge Closure

For the third year in a row, Caltrans closed the San Francisco – Oakland Bay Bridge during Labor Day
Weekend while work was done on the bridge. A 300 foot long section was removed and a new section was moved into place connecting the east span with a new detour span at Yerba Buena Island. To do this, Caltrans chose to close the bridge from Thursday at 8 PM through Tuesday at 5 AM.

The Bay Bridge is a popular route for both commuters and visitors alike. The AADT runs nearly 250,000 vehicles per day. A large public outreach effort was made including ads on TV, newspapers and radio; two websites (www.baybridgeinfo.org and http://baybridge360.org ); Twitter and YouTube (http://youtube.com/BayBridgeInfo ).

There were also dozens of portable and permanent changeable message signs placed along key routes warning of the closure. Traffic was definitely reduced by these efforts but volumes still increased on alternate routes. There were three main detours. To the north is the Richmond – San Rafael Bridge connecting to 101 and the Golden Gate Bridge. To the south there are two options. The closest is the San Mateo Bridge and nine miles farther south is the Dumbarton Bridge.

When the Bay Bridge was closed the past two years, the most serious backups occurred at the east end of the San Mateo Bridge and at the transitions between 101 and 580 in San Rafael in Marin County.

Caltrans therefore chose to place 5 iCONEs on 92 just west of 880, 3 to monitor east bound traffic and 2 to monitor west bound traffic. They also placed 8 iCONEs in Marin County – 2 on 580 west bound, 3 on 101 north bound and 3 on 101 south bound.

The iCONEs were primarily used to monitor queue lengths. They expected some queuing. But wanted to know immediately when delays got worse. As it turned out, traffic wasn’t too bad. The queues did exceed their targets a few times but only briefly so Caltrans never needed to divert traffic to other alternate routes.

After the closure Caltrans reviewed the data to learn where problems did occur and why. They already had the “big picture” provided by loops and cameras showing how traffic moved around the Bay Area during the Labor Day Weekend. They know what the counts and volumes are for segments of each route. But the iCONEs gave them a more granular “micro” view at key locations. They can see exactly where the backups began and learn how they ebbed and flowed during the weekend. This will help them identify some of the causes of slowing so they can work to minimize those even further when they close the bridge again next year.

Road-Tech Safety Services of Elk Grove, California is the local distributor. They placed 9 of the devices while Caltrans placed the other 4. Road-Tech monitored their performance throughout the weekend and picked them up after the bridge was reopened.

The iCONEs performed very well. Dale McCrossen, Caltrans’ Lane Closure Manager for the Bay Area said “The iCONEs were like having several people standing by the road to monitor traffic. They helped him leverage his time and allowed him to, in effect, be in several places at one time”.

Mr. McCrossen was very happy with the data from most of the iCONEs. But, he was not with the one east bound on 92 just prior to the 880 interchange. That particular device always showed slow or stopped traffic. But traffic is slow there even when the Bay Bridge is open. So he moved it farther west on 92 past the toll
plaza out onto the bridge itself to learn if queues backed up that far. They did for a few short periods, but that told him the extent of the queue and gave him a good idea of the length of the delays through that
interchange.

The ease with which the iCONEs were deployed made them ideal for events of this kind. They worked well,
were easily relocated when necessary, were very cost effective and the resulting data will help Caltrans to plan future closures.