Bridging the Gap: The Broad Causeway Bridge

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Markets

Buildings & places

Transportation

Water
Location

Florida, United States
Client

The Town of Bay Harbor Islands
Completion date

2031

David Konz

Technical Manager II, Tampa, Florida, United States of America contact form+1 813 281 5458

Felipe Jung

Business Development Manager, Miami, US contact form

Using detailed 3D visualizations and walkthroughs to model bridge designs and secure informed community support

Aging infrastructure is a big problem.

It’s expensive to replace, expensive to keep repairing, and can be difficult for communities and taxpayers to get excited about. But as materials degrade and patterns of use change, it is vital that we address these challenges.

The Broad Causeway Bridge spans Biscayne Bay and the Intracoastal Waterway (ICWW) and has connected the Town of Bay Harbor Islands to the mainland Miami Metro area for 73 years. This aging bascule bridge sees 23,000 vehicles per day, providing access not only to residents of the Town of Bay Harbor Islands, but to millions of tourists travelling to Miami beaches every year and as a key emergency evacuation route. After so many years of service, the bridge is rapidly deteriorating and will require heavy maintenance in the future – something that will be both costly and inconvenient for the community it serves. As design and safety standards have changed, the bridge is also now listed as “Functionally Obsolete” according to FHWA rules, with certain safety aspects like shoulder width and lane width no longer meeting design standards. In January of 2024, the bridge was downgraded to “Structurally Deficient”, leading to temporary lane closures and weight restrictions.

The Town of Bay Harbor Islands began the process of replacing this bridge in August 2022, engaging the AtkinsRéalis team to provide consulting, planning, feasibility and environmental studies, concept design, final design and construction engineering services.

Play button

Town of Bay Harbor Islands Broad Causeway Bridge

Watch the video or try the virtual walkthrough of the proposed 65-foot fixed bridge.

Try the virtual bridge walkthrough About Town of Bay Harbor Islands Broad Causeway Bridge

Manatees, yachts and stunning views

Before the bridge could be designed, the team first had to complete an ecological survey, to understand how the project might impact the local environment.

Biscayne Bay Aquatic Preserve that the bridge crosses is home to a variety of important marine species, including fish, corals, manatees and sea turtles. Consequently, we would need to carefully plan how to minimize and mitigate the impact of any new construction through regular monitoring, transplanting and relocation of at-risk specimens, and potentially the establishment of offsite preservation banks.

The location also brings other challenges, such as vertical clearance requirements for larger boats and yachts. The ICWW is managed by the US Coast Guard, who established guide clearance for fixed bridges to be 65-feet high to meet the reasonable needs of navigation. The existing bridge opens to meet this requirement, but the frequency of these openings combined with the heavy traffic can cause significant tailbacks and increased air pollution, and the community wanted to explore options that avoided this problem. A taller bridge also offers impressive views of the Miami Skyline and Biscayne Bay, and the 65-foot fixed option includes pedestrian viewing balconies to make the most of this scenery.

The new structure would also have to be resilient to rising sea levels and extreme weather to ensure its sustainability as a long-term solution.

A member of the public tries the VR walkthrough

A view from the bridge

One big challenge that communities often face with major projects is visualizing the changes. During early stages like planning and public engagement there are no building sites or structures to view, just an empty lot waiting for construction to start. This can make it difficult for stakeholders to visualize elements, making communication and decision making difficult.

To tackle this, the AtkinsRéalis team developed a live “digital twin” for the project, allowing residents and decision-makers to see the proposed bridge structures as they would look in their community. This meant not just modelling the bridge in detail, but also the landscape around it, individual streets and houses in the town, and pedestrians, motorists and even picnickers. Stakeholders could see the proposed bridges from every angle and understand both how it might look on an average day, and how it might impact other parts of the town, for example by the addition of pedestrian crossings.

One major change between the old bridge and the two proposed options was the creation of a dedicated walkway for pedestrians and bicyclists with barriers that protect users from traffic. Many members of the community didn’t necessarily understand why this was needed, as they had only ever driven over the existing bridge or didn’t use a wheelchair or walker. So the team developed a VR (virtual reality) version of the existing bridge, allowing residents to experience how vulnerable the narrow walkway felt with the traffic rushing past, and how it compared to the proposed changes, which are Americans with Disabilities Act (ADA) compliant. This created increased community support for the change, and real excitement for the project.

A view of the proposed broad causeway bridge

Informed decision making

The community explored three proposals in total:

Construction of a 65-foot fixed bridge
Construction of a 40-foot movable bridge
A No-Build alternative, where the town continued to maintain their existing bridge

With the help of the detailed bridge simulations, they selected the 65-foot Fixed Bridge Alternative, allowing us to move to the next phase of the project a full six months ahead of schedule.

The community will continue to be consulted about design choices, and the team is currently building a 3D walkthrough of the bridge and surrounding area in which to model these options. Residents will be able to see and compare suggested design elements such as lighting and landscaping as they will look in real life, allowing them to make informed decisions and ensuring that the new bridge perfectly fits the needs of the community it serves.