August 5, 2008
GOLDEN GATE BRIDGE MOVEABLE MEDIAN BARRIER PROJECT
A Request for Proposals to hire consultants to assist the Golden Gate Bridge, Highway and Transportation District (District) with the preparation of the required engineering and environment analysis was issued on June 6, 2008, with proposals due on July 14, 2008. It is anticipated that a contract could be awarded in early September 2008, with work starting shortly after that.
Golden Gate Bridge Accident Rate is 3 times Lower Now than in the 1980s
The accident rate on the Golden Gate Bridge is now three times lower that what it was in the 1980s largely due to the reduction in the speed limit, enforcement, and driver education and awareness. Since 1970 there have been 36 fatalities of which 16 were from head-on collisions. The smooth and safe flow of traffic across the 1.7 mile long Bridge has been enhanced through a number of operational and safety features including the reduction of the speed limit to 45 MPH, increased law enforcement patrols and increased use of radar, and establishing the Bridge as a special driving zone.
Moveable Median Barrier System
With its narrow roadway lanes and tight curves at either end, coupled with its traffic volumes, and frequently foggy and windy conditions, the installation of a one-foot-wide moveable median barrier (MMB) is a proposed safety enhancement intended to eliminate crossover collisions on the Golden Gate Bridge. The MMB system includes the barrier—12-inch wide and 32-inch high steel clad units filled with high density concrete tightly pinned together to form a semi-rigid median barrier—and the barrier transfer machines.
Summary of Actions 1996 to 2008
In 1996, with the emergence of a new and narrower one-foot wide barrier, the District immediately launched a comprehensive analysis that lead to the conclusion that, with some operational trade-offs, a barrier will virtually eliminate crossover accidents. On July 12, 1996, the Board by Resolution 96-163, authorized the District’s financial participation, in the amount of $42,500, in the crash test of the new BSI one foot wide MMB. The Board also authorized engaging services of Northwestern to evaluate various traffic and safety ramifications of the installation of the new one foot wide MMB on the Bridge.
Following crash testing in March 1997, Northwestern completed its report titled Traffic Safety Study dated October 29, 1997. Professor Robert K. Seyfried, Northwestern, presented the findings of the report to the Building and Operating Committee of the Board in December 1997. Professor Seyfried explained that the report concluded that the decision is a virtual toss-up, and the Board could reasonably make a decision either way—install a MMB or forgo installation of a MMB. The Board’s final decision must result from a balancing of factors and considerations, which in turn would require the Board to determine which considerations and factors are most important.
On May 22, 1998, the Board, by Resolution 98-116, authorized a conceptual approval for the installation of the BSI one foot wide MMB on the Bridge and authorized staff to investigate acceptable solutions to the many remaining technical and operational items (approximately 28 different items) that must be resolved prior to installation. Additionally, the Board directed staff to develop a cost estimate for the MMB installation, identify necessary permits, and to begin to identify possible funding sources.
A phased approach would be implemented to resolve the many remaining technical and operational issues identified as part of the May 1998 conceptual approval process.
In August 1999, the Board authorized the first of several studies of some of these unresolved technical and operational issues as part of a preliminary engineering evaluation and, by Resolution 99-175, authorized Parsons Brinckerhoff (PB), San Francisco, CA, to perform the following services, as Phase I, relative to the possible installation of a MMB:
- Evaluate MMB end treatment and anchorage schemes at the toll plaza.
- Evaluate storage requirements for the Barrier Transfer Machine (BTM) at the north end.
- Evaluate strategies for delineation of traffic lanes on the Bridge with a MMB installed.
- Develop emergency response procedures for accidents or incidents that require emergency response across or through a MMB.
PB’s findings were presented in two reports: 1) Conceptual Engineering Design Studies and, 2) Emergency Operations Report. PB concluded that possible engineering solutions may exist for those aspects of a MMB installation that were studied, subject to further design and development during a future detailed engineering design phase, provided that the Board accept the various trade-offs involved in those proposed solutions. PB also concluded that existing emergency response procedures would have to be modified and/or supplemented to provide satisfactory emergency response with a MMB present, again with the recognition that such procedures may have certain drawbacks and involve certain trade-offs.
On March 9, 2001, by Resolution 2001-044, the Board accepted PB’s findings and authorized PB to conduct Phase II studies:
- Evaluate the traffic congestion impact of decreasing lane widths on the Bridge with the MMB installed.
- Evaluate the impact of the MMB on traffic congestion associated with traffic accidents and stalls on the Bridge.
In January 2002, PB reported their findings in Movable Median Barrier Feasibility Studies—Phase II and provided the following conclusions:
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Placing a MMB on the Bridge will result in decreased lane widths in at least two lanes at any one time. While there is no “perfect” lane configuration, there are several potentially viable lane configurations, each of which, however, has certain drawbacks.
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Installation of a MMB on the Bridge could theoretically result in a reduction in capacity in the two- and three-lane configurations, but it is also possible that this capacity reduction may not occur. The ultimate result is not certain.
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Installation of a MMB on the Bridge would result in a virtual elimination of crossover head-on accidents. Head-on fatal accidents occur less frequently than other types of accidents; but this type of accident causes significantly greater delays per accident.
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Installation of a MMB would result in certain other types of accidents (e.g. rear enders in the two lane direction) being more difficult to clear due to the presence of the barrier, resulting in longer delays than the current condition for these accident types. It is assumed that the introduction of a MMB on the Bridge will not result in a change in the overall accident rate, but this is not certain.
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The elimination of delays associated with crossover accidents might be offset by the increase in delays caused by non-crossover accidents. Over the course of a year, as opposed to a per incident basis, overall delays associated with accidents may not significantly change, but again this cannot be predicted with certainty.
The Phase I and Phase II studies performed by PB did not address all of the technical and operational issues identified previously in Resolution 98-116 authorized by the Board on May 22, 1998. However, of the issues that were studied, none categorically ruled out installation of a MMB on the Bridge, but as reported in the findings, the possible resolution of those issues involved balancing of pros and cons and acceptance of trade-offs.
To address the remaining technical and operational issues outlined in the May 22, 1998 Resolution 98-116, and to answer many of the final operational, engineering and cost details, it is necessary to proceed with detailed design and environmental studies.
On April 12, 2002, the Board, by Resolution 2002-045, approved the following actions:
- Accept PB’s January 2002 Movable Median Barrier Feasibility Studies–Phase II Report.
- Direct staff to develop a funding plan for detailed design and environmental studies.
On March 11, 2005, as part of Resolution 2005-015, the Board authorized the Board President to form an Advisory Committee of the Board for Bridge Barrier Projects to work with staff to identify and pursue funding for implementation of the studies associated with both the Physical Suicide Deterrent System and the MMB system projects.
In late 2007 and early 2007, required Wind Tunnel Testing was conducted on the MMB. When any modification is contemplated for the Golden Gate Bridge, it is essential that they are tested for wind stability to ensure that there is no negative impact to the wind dynamics of the span. Wind tunnel testing was done on the MMB in conjunction with three generic design concepts for a suicide barrier on the span. It has been determined that a MMB can be added safely to the Bridge without negatively impacting the wind stability of the Bridge.
In June 2008, a Request for Proposal will be issued to solicit consultants to work with the District to complete the legally required detailed design and environmental studies. It is envision that we will see a moveable median barrier on the Bridge within 24 to 36 months.
Simulated image of the “zipper” truck moving a MMB on the Golden Gate Bridge:
Existing Reversible Lane Changing System Instituted in 1973
The span’s six-lane roadway includes curb lanes that are 11-foot-wide and the remaining four lanes are just 10-feet wide. Traffic travels across the span in opposing directions separated by 19 inch-tall, 4 inch diameter plastic tubes, spaced at 25 foot intervals. The tubes are manually placed in sockets in the Bridge roadway to identify the San Francisco outbound lanes and San Francisco inbound lanes and are reconfigured several times per day to match the direction of peak traffic flow.
Additional Moveable Median Barrier Background 1939 to 1985
Original construction of the Bridge roadway, in 1937, provided six 10 foot wide lanes. This was in conformance with standard practice of that era and was considered entirely adequate for safe operations of passenger cars and trucks, and, at that time, any anticipated future needs.
As early as 1939, District Engineer Mr. Russell G. Cone was requested by the Board to investigate the possibility of installing a dividing curb or barrier on the Bridge’s centerline, following a fatal accident involving a head-on collision. In September 1939, Mr. Cone consulted with Mr. O.H. Ammann, then Director of Engineering of the Port of New York Authority, and former consultant to the Board during design and construction of the Bridge.
After discussions with Mr. Ammann, Mr. Cone determined that the installation of a concrete centerline barrier would leave room for only two lanes of traffic in each direction and that this lane configuration would be insufficient to accommodate future traffic demands.
The discussion of installing a centerline barrier did not resume again until the 1960s, as by that time traffic density and speeds on the Bridge had increased significantly. With the implementation of reversible lanes in 1963, a potential median barrier would have to be movable to accommodate peak traffic flow patterns, and at the time, no such barrier had yet been developed.
The concept of a possible centerline barrier was not raised again until 1979. During the design phase of the Bridge Deck Replacement Project (see Chapter 6), it was determined that the original 60 foot wide roadway could be replaced with a 62 foot wide steel plate roadway. Barrier proponents proposed that the additional two feet of roadway width should be utilized for the installation of a barrier. Since there was still no viable movable barrier in existence, a fixed barrier that would divide the roadway into three lanes in each direction was proposed. Mr. Bernard C. Johnson, Consulting Traffic Engineer, was retained by the District to determine if installing a fixed median barrier would result in additional roadway safety.
Mr. Johnson, in his report to the Board, stated that a fixed barrier would not be appropriate as traffic congestion impacts would result with only three lanes in either direction during peak traffic periods, and he also noted that a fixed barrier would detract from safety by resulting in an increase in rear-end collisions. The Board, on November 9, 1979, by Resolution 10,640, directed staff to proceed with the Bridge Deck Replacement Project design with no median.
During the early 1980s, several movable median barrier (MMB) concepts were proposed by the public that led to further study. On April 29, 1983, by Resolution 83-139, the Board retained Sverdrup & Parcel (S&P), San Francisco, CA, to perform a preliminary feasibility study of the four most promising moveable median barrier (MMB) concepts: Wattenberg Pipe Barrier; Carson Type 50 Barrier; Stone and Booth Inverted Tee Barrier; Pace Modified Type 50 Barrier.
S&P’s November 1983 report to the Board, Moveable Median Barrier Feasibility Study, concluded that, although it was possible to design a MMB from a technical engineering standpoint, such a MMB would only be marginally effective in reducing the total accident hazard on the Bridge and would not be cost effective under generally accepted standards of that time. S&P determined that, based on AASHTO selection criteria for barriers, it could not recommend the use of a MMB on the Bridge.
NASA’s Ames Research Center (NASA Ames), Moffett Field, CA, working with Lawrence Livermore Laboratory (Lawrence Livermore), Livermore, CA, then performed an analysis of the S&P findings as well as an independent analysis of the concept of a MMB as it applied to the Bridge. On February 24, 1984, their preliminary report presented to the Board concluded that the primary basis for determining whether to proceed with development of a MMB should be based on traffic safety engineering considerations. They further recommended that MMB performance elements be defined with the assistance of an independent, experienced agency and that MMB design concepts be resolicited to conform with these performance elements. The most promising concepts would then be selected for detailed analysis, design, and testing. The Board accepted these recommendations by Resolution 84-80.
On April 13, 1984, the Board, under Resolution 84-104, approved specified performance, operational, and maintenance elements as standards governing design of a possible MMB. These elements were later refined, by Resolution 84-172 on June 8, 1984, after further consultation with NASA Ames, Lawrence Livermore, A&W, and Caltrans. Resolution 84-104 had also established a program for the development of a prototype MMB.
On October 12, 1984, the Board, by Resolution 84-332, authorized execution of an agreement with the Traffic Institute of Northwestern University (Northwestern), Evanston, IL, to perform an analysis to determine the effect of the installation of a two foot wide MMB on Bridge traffic capacity and safety. Their August 30, 1985 report to the Board concluded that, due to the unique characteristics and conditions represented by the Bridge and its approaches, installation of the then proposed two foot wide MMB would be inappropriate. On August 30, 1985, the Board, by Resolution 85-293, accepted the Northwestern report and resolved that, “The Board of Directors, in light of the exhaustive analysis and evaluations that have been conducted by District staff, independent governmental agencies and engineering consultants to determine the feasibility of the moveable median barrier on the Golden Gate Bridge, hereby finds and declares that a movable median barrier is inappropriate for the Golden Gate Bridge.”