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Ten Mile Bridge Replacement Project

News and Developments

The Ten Mile Bridge is the third replacement project of Caltrans on scenic Highway 1 in Mendocino County.

The first one, the Noyo Bridge, led to a protracted, ultimately successful effort to get Caltrans to use a railing design that was visually pleasing, protected pedestrians, and allowed virtually unobstructed views.

The second one, the Greenwood Bridge, in the small village of Elk, led to another so-far-successful battle (as of June 2006) to protect the coast from an urban-expressway style bridge.


Ten Mile Bridge is located in a rural, ecologically sensitive, and scenically beautiful location in Mendocino County.

In Fall, 2005 Caltrans proposed to replace this bridge with one that is completely out of character and scale, lacks a protected sidewalk, and uses a railing that obscures views and lacks any grace or historic character. Caltrans made this proposal despite Coastal Commissioners expressing their opposition to it at an earlier hearing on the Greenwood Bridge.

The 8' shoulders will give the bridge the appearance of a high-speed expressway, rather than a scenic bridge on a rural road.

The lack of a sidewalk will endanger local people and those using the Coastal Trail.

The proposed ST-20 railing for the east side is appropriate for a cattle gate, not a scenic bridge


A sidewalk with a protective rail on the inner, traffic side, as on the Noyo Bridge,  would be much safer. A newly designed outer pedestrian rail would be more aesthetic and less visually obtrusive to motorists and, especially pedestrians and bicyclists.

A hearing before the Coastal Commission was scheduled for November 2005. The task of defeating this project was made doubly difficult by the crucial support of the Commission staff for the Caltrans design. Because of the overwhelming amount of information that confront the Commissioners at every monthly meeting, they rely heavily on the recommendations of the staff.

For detailed support of recommended amendments, see  Ten Mile Bridge testimony to the Coastal Commission (requires free Adobe Acrobat Reader). Caltrans arguments for 8' shoulders are completely unsupportable, based on an analysis of state and national design standards, design exceptions, and accident data.

The Coastal Commission staff report on the Ten Mile Bridge is at:
www.coastal.ca.gov/cd/W20b-11-2005.pdf. There is a long, tortured attempt to rationalize the acceptability of 8' shoulders on pages 17-22. It is not convincing.

The Ten Mile Bridge effort is part of a campaign to preserve scenic views and the rural character of bridges along coastal Highway 1. Find out more.

News and Developments

Ten Mile Bridge Opens

On Friday, May 8, 2009, at 1:00 p.m. the official opening of the new Ten Mile Bridge was celebrated.

The final result can justly be celebrated as a symbol of what community action, the Coastal Commission, and Caltrans working together can achieve.

The initially proposed bridge would have been much larger and uglier and done unnecessary damage to rare environmental and scenic values.

As a result of community opposition to the initial design, Caltrans worked with the community and the Coastal Commission to come up with a  design that was smaller, better aligned, incorporated a pedestrian walkway, and a newly designed railing that preserved scenic views and is aesthetically pleasing. It revised its plans and construction methods to protect the wildlife and fish of this amazing sanctuary. During the opening ceremony, a deer passed below in back of a speaker. An osprey flew up right over the bridge, evidently to see what was happening. Many birds and a seal were in the water below.

Looking up 10 Mile Estuary through new combo rail

At the opening ceremony, all of the Caltrans staff that worked on the project acknowledged the value of the review by the Coastal Commission and the critiques provided my the local community. They all felt that the bridge was better because of, even though their tasks were made more difficult.

District Director Charlie Fielder  was generous in his praise for my contributions to gaining a better railing design.  The final design was due to the combined efforts of me, the Coastal Commission Committee on Bridge Railings, and Roberto LaCalle of Caltrans. All are happy with the final result.

Ten Mile Bridge Nears Completion

March 26, 2009. I paid a visit to the site of the new Ten Mile Bridge, which is nearing completion. The new combination bicycle-automobile railing is now in place, though not painted. It looks splendid in this beautiful setting.

A closer look reveals a design flaw that could represent a hazard to bicyclists:

The upper part of the railing is set back from the automobile crash barrier, creating a gap between the two that is potentially hazardous to cyclists. I urged at the time that this gap be eliminated, but Caltrans objected on time-issues and motorist safety concerns, and the Coastal Commission supported Caltrans.

Because the combo railing is visually attractive, it is likely to be used on other scenic bridges, including the upcoming rebuild of the Greenwood Bridge in Elk. Now is the time for Caltrans to do the redesign and testing necessary to create an integrated design.

New Design for Ten Mile Bridge Railing

September 9, 2007, Eureka. Working together with the Railing Subcommittee of the Coastal Commission, Caltrans developed a much improved railing design for the new Ten Mile Bridge.

A key to the improved design was the decision by Caltrans to accept a 42-inch height for the bicycle railing (as compared to the previously required height of 54"). This height conforms to the height adopted by AASHTO, the national highway standards organization in May, 2006.

Caltrans was initially opposed to accepting the 42" national standard. I provided Caltrans and Coastal Commissioners with data and argument in support of this standard. Caltrans determined that it would need to do its own internal review of the appropriate height.

The decision to use a 42-inch railing allowed the east railing, which needed to protect for both cars and bicyclists, to be based on the visually transparent and pleasing ST-10, with the addition of a smaller top railing at 42". At the request of the Bridge Railing Subcommittee, curved elements were placed between under the top railing down to the height of the second structural member of the ST-10. The result can be seen in the "elevation view" in the photo above.

What isn't apparent in these views is that the top railing is set back 15" from the front of the ST-10. This creates a 7" gap between the back of the ST-10 rail and the bicycle railing. I argued, unsuccessfully, that this created a safety hazard for cyclists and that the gap should be eliminated. Caltrans stated that it would be too time consuming and expensive to develop a design without the gap. The Commission staff supported the Caltrans design (see staff report).

The Coastal Commission approved the proposed Caltrans railing on September 9, 2007. Although there are some concerns about the approved railing with respect to cyclist safety, these concerns are relatively minor compared to the huge improvement in aesthetics and transparency compared to the initially proposed design.

The Ten Mile Bridge is scheduled for completion in 2009.

More on the history of Ten Mile Bridge project

Ten Mile Bridge
Good and not-so-good news

June 10, 2006, Santa Rosa. The Coastal Commission approved without discussion a revised Caltrans proposal for the Ten Mile Bridge. The revised design has a single five-foot sidewalk on the west side, six-feet shoulders on both sides, and a combination auto-bicycle railing on the east side.

The revised design was Caltrans' response to the Commission's November, 2005, specification of four-foot shoulders and sidewalks on each side of the bridge. From the standpoint of preserving the scenic values of Ten Mile River, the revised design is mixed. On the positive side, the single five-foot sidewalk reduces the scale of the bridge as compared to two four-foot sidewalks. The six foot shoulders are unnecessarily wide from an automobile safety standpoint, but five-foot shoulders are recommended for bicycle safety; thus the arguably unjustified width of the bridge is only two feet.

In a welcome move, Caltrans and the Commission agreed to defer for a year choosing a design for the railings on the bridge. The design of the railing for the east side of the bridge is challenging, because it will need to protect bicyclists as well as cars. The initial design proposed by Caltrans was a visual catastrophe suitable for a cattle gate, but not a scenic bridge.

Since November, Caltrans and a subcommittee of the Commission have been working on developing alternative designs. I was invited to assist the subcommittee and have been doing so. To date, no really attractive designs have been developed, but Caltrans seems open to meeting the concerns of the Commission and the public.

[Just this week, (June 27, 2006) I received extremely good news that creates a much greater probability of making a visually attractive and transparent design for the east railing: the national highway standards organization followed by Caltrans has just lowered the bicycle railing height from 54" to 42" (the same as pedestrian railings). This will improve enormously the aesthetic possibilities for railing designs.]

The most discouraging aspect of the Ten Mile decision was the Commission's acceptance of bogus "safety data" from Caltrans. The Commission staff and ultimately the Commission accepted the wider shoulders because Caltrans asserted that moving from four to six foot shoulders would reduce accidents by 44 percent.

I was not provided the source of the Caltrans safety estimate until after the Commission staff had published its staff report, too late to provide correct information to the staff and too late even to get written comments to the Commissioners until the night before the hearing. It is doubtful that any Commissioners even reviewed my written testimony (free Adobe Acrobat Reader, if needed). Although at the hearing, I that showed that there was no empirical basis for Caltrans' safety assertion and that there was no significant vehicle safety benefit from the wider shoulders, it was too little too late.

On the positive side, Caltrans has invited me to work with me on future bridge designs prior to submitting permit applications to Caltrans. I've accepted the invitation and hope to come to resolve our differences around safety arguments. The evidence on shoulder width and safety is very clear. I am optimistic, therefore, that future coastal bridges will be built with the five-foot shoulders that are needed to for cyclist safety and no wider.

All in all, progress is being made, largely because of the outpouring of public support for bridge designs that protect the scenic values of our beautiful North Coast.

Thank you for your help and support.

June 10, 2006, Santa Rosa. The Coastal Commission approved without discussion a revised Caltrans proposal for the Ten Mile Bridge. The revised design has a single five-foot sidewalk on the west side, six-feet shoulders on both sides, and a combination auto-bicycle railing on the east side.

The revised design was Caltrans' response to the Commission's November, 2005, specification of four-foot shoulders and sidewalks on each side of the bridge. From the standpoint of preserving the scenic values of Ten Mile River, the Commission's latest action is mixed. Overall, though, progress is being made.
More details. Other Ten-Mile news.

Bicycle Railing Height Standard Reduced

May 2006. Perhaps the most important action for preserving vistas was taken recently by the national highway standards organization (AASHTO).

At its May, 2006 meeting, the bridge committee lowered the railing height for bicycle railings from 54" to 42", the same height as pedestrian railings. This change will improve enormously the aesthetic possibilities for railing designs. This is important for Ten Mile Bridge and all other bridges on Highway 1 where combination auto-bicycle railings are needed.

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