March 26, 2010

Updated March 29, 2010

Northbound Afternoon Commute Lane Configuration Challenge at Golden Gate Bridge Current Afternoon Configuration is 3 Lanes South and 3 Lanes North

 

Golden Gate Bridge lane configurations are based on real-time traffic demand and to accommodate extenuating circumstances such as accidents or special events, with the underlying goal of providing reasonable mobility for everyone without causing excessive hardship to anyone.

Effective Monday, March 29, 2010, in response again to changing traffic patterns, the Golden Gate Bridge roadway will return to being configured with 3 lanes south into San Francisco and 3 lanes north out of San Francisco during the afternoon weekday commute period. If you would like to comment on this topic, please email bridgecomments@goldengate.org.

 

MORE BACKGROUND ON GGB LANE CONFIGURATIONS

The Golden Gate Bridge is 1.7 miles long and has six roadway lanes that can be configured to provide 3 or 4 travel lanes in either direction at different times of day with the goal of balancing mobility for both north and south motorists. The underlying goal is to benefit the largest number of motorists without creating excessive delays for any. For example, during the morning commute, the roadway is configured to provide 4 roadway lanes into San Francisco and 2 roadway lanes north out of San Francisco.

Golden Gate Bridge lane configurations are established based on time-of-day traffic demand trends that are constantly being monitored and evaluated. Lane configurations can also be changed to accommodate extenuating circumstances such as accidents or large special events such as baseball games at AT&T Park. This is a delicate balancing act that becomes very difficult when demand is heavy in both directions at once, or when stalls, accidents or other incidents on the roadway interfere with the normal flow of traffic in either direction.

Lane configurations can also be changed to accommodate unusually heavy demand in one direction or the other. However, the time required to reconfigure the lanes on the Bridge and Doyle Drive takes approximately 30 minutes and can take much longer if the lane changing trucks are in heavy traffic enroute to the location to make the lane change. These unusual circumstances are also often transient in nature and delays often resolve themselves in the time it takes to make lane adjustments. For these reasons and because, in general, motorists favor predictability in lane configurations, “impromptu” lane configurations changes are avoided whenever possible.

During the morning commute, from approximately 6 am to 9 am, traffic patterns across the Bridge are very predictable and are such that a standard 4 lanes south into San Francisco and 2 lanes north out of San Francisco is successful for mobility in both directions.

Afternoon traffic is less predictable, but can almost always be accommodated with three lanes in each direction. However, there is often congestion on Doyle Drive leading up to the Bridge due to a number of factors that include:

  • A recent and dramatic increase in the number of vehicles merging onto Doyle Drive from 19th Ave and Merchant Road near the toll plaza due to Doyle Drive construction.
  • Less than ideal lane geometry in these merge areas.
  • A general increase in traffic on Doyle Drive and the Merchant Road merge due to increased development in the Presidio over the last few years.

Typical recent southbound traffic demand has routinely exceeded 4,000 vehicles per hour during the evening commute. This is more traffic than can be accommodated in only 2 lanes. If there were to add a fourth lane northbound, forcing southbound traffic into two lanes would very quickly cause a backup onto the Waldo Grade, which is the condition that was observed on most weekday evenings during December, January February and March. At the same time, northbound demand has been running at about 5,100 vehicles per hour, which can be reasonably accommodated in three lanes without causing undue delay. These trends, and the mounting frustration of southbound motorists facing nightly delays of 30 minutes or more, prompted GGB officials to make the decision to configure the roadway in 3 north/3 south configuration for the evening commute effective March 26, 2010.

Another factor that can impacted the traffic is that when the roadway is at or near capacity, any minor stall or accident can cause dramatic backups that can take hours to clear.

Summary of Afternoon Lane Configuration Patterns

The greatest challenge comes during the afternoon commute period of 4 pm to 7 pm.

When

Routine

Afternoon Lane

Configuration

Comments
Prior to 2002
4 North/2 South
Board policy is to favor northbound commute direction
2002 to November 1, 2009
3 North/3 South
Due to increased southbound traffic and decreased northbound traffic during the evening hours, the change was instituted.
November 2, 2009 to March 26, 2010
4 North/2 South
Due to increasing northbound demand and relatively stable southbound demand that could be accommodated in 2 lanes, the change was instituted.
March 29, 2010 to present
3 North/3 South
Due to rapidly increasing southbound demand starting in about December 2009 that caused long delays for southbound motorists combined with relatively stable northbound demand, the change was instituted.