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Data Show Bay Bridge Crossing Speeds Not Affected by Variable Tolls

Graphic: Eric Fischer
Graphic: Eric Fischer

When the tolls on Bay Area bridges were increased on July 1, the Bay Bridge was given a higher toll at the times of its greatest usage in an attempt to reduce congestion by discouraging drivers from using the bridge at peak times.  Crossing the bridge into San Francisco costs $6 from 5:00 to 10:00 am and 3:00 to 7:00 pm on weekdays, $4 at other times on weekdays, and $5 on weekends.  However, the toll structure does not seem to have had the desired effect.

Using data for about 50,000 bridge crossings from Stamen Design's Cabspotting and from NextBus for AC Transit, I calculated and plotted the time required to cross the bridge at different times of day before and after the toll increase.

The graphs are noisy because of the small sample size, but the time required to cross the bridge by car at the morning and afternoon weekday peak times seems basically unchanged since 2008.  The off-peak weekday crossing is a little slower than it used to be, perhaps because of the S-curve detour for construction of the new east span.  On weekends, the off-peak crossing time seems to be unchanged since 2008.

The weekend peak data from 2008 is especially noisy so it is hard to tell exactly what has changed there, but if anything, it takes longer to cross the bridge now than it did before.  It seems that either the demand for the bridge is so inelastic that the variable tolls are not an effective way of shifting or reducing demand, or that the price differential has not been made large enough to have an effect.

What does seem to be effective is the exclusive bus lane that allows AC Transit buses to cross the bridge nearly as quickly during the morning weekday peak as at off-peak times.  I don't understand why it doesn't provide the same benefit during the afternoon peak.

Graphic: Eric Fischer
Graphic: Eric Fischer

John Goodwin, a spokesperson for the Metropolitan Transportation Commission, said it's too early to draw any conclusions but a group of UC Berkeley professors, including Robert Cervero, was hired to do a comprehensive analysis of the new toll schedule, including the impact on the Bay Bridge. Some preliminary results are expected to be released next week.

"It's still far too early to draw any meaningful conclusions but we're very much interested in getting as much data as we can. We're certainly looking forward to receiving the initial findings," said Goodwin.

A report [pdf] released by the MTC in October showed that Bay Bridge traffic did not significantly decline in 2010 when compared to 2009.

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