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Proposed Movable Barrier System

System Design By 
Robert M. Guernsey & Associates/Conceptualist in Design & Engineering
46 Elm Avenue ~ San Anselmo, CA. 94960-2210

                                                   

Summary:  The Board of Directors of the Golden Gate Bridge, Highway and Transportation District were considering installing a movable median barrier to separate opposing directions of traffic on the Golden Gate Bridge in 1985. The bridge is a six-lane structure that connects an eight-lane divided freeway from the north to the city of San Francisco via Doyle Drive to the south.

    The bridge lanes are divided with a reversible lane system consisting of a plastic cone, set into a small hole every twenty-five feet in the road surface, providing four traffic lanes in one direction and is moved periodically to accommodate traffic flow during non-peck hours in other directions.  This method in separating lanes of traffic has proven to be an ineffective method, by placing the motorist in a high-risk of danger at all times under current road conditions, with unprotected, and undivided lanes across the bridge. Therefore, the Board has directed that any barrier considered for the bridge would have to be movable to accommodate this traffic lane allocation pattern.  Previous engineering studies have determined the feasibility of developing, installing, and operating a movable barrier on the bridge. For the purposes of conducting a new study, it is assumed that the conclusions of such study will concern the technical feasibility of such a barrier are valid. 

    The Northwestern feasibility study on a movable median barrier, they were very concerned over the proposed concrete movable barrier and the application of it. " We are concerned that this accuracy in barrier placement may not be possible. Test under realistic field conditions should be performed to determine whether the barrier can be transferred with reliable accuracy."  In addition, if such placement accuracy is not likely in actual practice, full-scale testing of any type of barrier should include an evaluation of the barrier that will serve as a barrier. The presence of the raised pavement markers may also affect the ability of bridge maintenance workers to manually reposition barrier alignment of a concrete movable barrier, and may cause some danger to the workers in doing so.

    By substantially reducing the barrier width, and using a rigid galvanized steel rectangular tube, the placement of the movable median barrier can be obtained at any given point, the rectangular tube is only two inches bigger than the raised white pavement marker, the original lane configuration of four and two- three and three, two and four and two-two-two can be maintained.  The proposed alternative method will answer several questions in the evaluating a new movable barrier system. The study by the Traffic Institute at Northwestern University, dated; July 1985, was based on several assumptions:

1.   Existing configuration on the bridge & approaches, two 11 foot outside lanes and four 10 foot inside lanes. 
2.   Existing practice of marking lanes lines with raised pavement markers. 
3.   All lanes should be at least ten feet wide and in no case should any lane be less than nine feet wide. 
    We feel that the Retractable Movable Barrier can show through engineering that the barrier will meet the bridge criteria needed to support the protection needed in preventing any head on-collisions.  Reference Fig 4. This illustration of the proposed Retractable Delineator median barrier; shows the relationship between the vehicles wheel-base, and the lane widths across the road surface from curb to curb. For examples; a Golden Gate Transit bus, a standard pick-up and a mid-size car.

    Segmented continuous interlocking barrier members that are embedded in the roadway, these sections replace the white line, and will be raised out of the roadway forming a continuous movable barrier from Doyle Drive to the North approach of Waldo Tunnel in Marin County, by aiding in prevention of any head on-collisions and serious injury accidents, and loss of life on this undivided roadway between opposing lanes of traffic. 

    All electro-mechanical mechanisms are controlled by a PLC programmable controllers, programmable on-site software data processor control workstation, fiber-optic's from north to south tower system's link-converter, mobile end user lap-top with hand held digital remote wireless link controller capabilities in a multi-environment in performing the tasks in altering lane configuration.

A performance schedule is set-up by the district in accordance with traffic flow determined by the bridge engineer and others, in the configuration of the pneumatic actuators and their sequence adjustment from existing lane configuration to the next new lane configuration simultaneously in order. Two safety vehicle needed to drive between the lanes during the change-over to assure traffic safety at all times, resulting in a smooth transition period between each change-over sequence.

The system will have two protective ground motion seismic sensor devices (both vertical & horizontal) will be tied into the safety circuits of the system, in preventing the system accidentally cycling lane configuration, in the event of an earthquake.
 
The Retractable Delineator Barrier Member:

    
                  
A twelve and a half foot piece of galvanized rectangular steel tube measuring; 2" x 6" x 3/8" affixed to a galvanized steel cased, with a pneumatic rod secured to the case and tube. Set into a frame mounted under road surface and secured with a rubber-mounts, affixed to bottom of cylinder housing, giving it flexibility and movability around 6.00".  The retractable barrier is comprised of two pneumatic cylinders per segments of twelve an one-half feet, times (x) 9151.46 feet, a total of 732 pneumatic cylinders making one complete barrier group across the bridge, times (x) three groups = 2,196 of actuating cylinders, whereby giving you three individual barrier groups needed for configuration in traffic control and traffic safety while across the Golden Gate Bridge. 

Once the system is on-line and operating, each change-over will approximately take from fourteen to eighteen minutes(14-18 min.) across the bridge. As one section is being lowered into the road surface, as this is completed, a new lane configuration will be raised out of the road surface at the same time. The retractable barrier members will
have raised pavement markers affixed to the exposed top surface. In addition, the retractable barriers lateral face will have a broken horizontal yellow and white strips/reflectorized, indicating direction of travel and will aid the driver of the vehicle, a visual sight line during early sunrise and sunset hours and late at night or in the fog. While not in use the retractable barrier will serve as the center line between the opposing lanes of traffic.

Doyle Drive Approach:

    Doyle drive has several unusual circumstances regarding how to solve the question of traffic control and preventing further head on-collisions. The structure of concrete and steel have sustained weather damage through old age, and may present some difficulty in traffic control and traffic flow.  The proposed Retractable median barrier consideration for feasibility for developing, installing, and operating of the retractable barrier on Doyle Drive, Richard Avenue, and Lombard Street, could be accomplished from the stand-point of separating lanes
of opposing traffic. 

    We believe that it could be possible, under existing conditions to incorporate the retractable movable median barrier from Doyle Drive approach, up to the toll booths, from the other side of toll booth across the bridge to the steel guard railing that separates northbound from southbound traffic in Marin County. A system of pneumatic lane pop-ups could be installed in the toll booth area as well. The pneumatic cylinders could be placed in a steel case with pneumatic devices. The approach to Doyle Drive would need several methods to divide this section of road
with a movable median barrier. 

    By setting the pneumatic in a steel box for pop-up's and putting into the ground through parts of Doyle Drive, on the anchorage, cut holes into surface and insert steel box, securing to the road surface creating a movable barrier.

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