The Cape Cod Bridges Replacement, Explained.

A plain-language guide to the $4.5 billion replacement of the Bourne Bridge and Sagamore Bridge, the main gateway onto Cape Cod. Pick a question to jump to the answer.

1. Why are the bridges being replaced?
2. When will the new bridges be ready?
3. What is a tied-arch bridge?
4. How will workers build them?
5. Will the bridges close during construction?
6. Who pays for it?
7. What is eminent domain, and who is affected?
8. What about people walking and biking?
9. Why do we have the Cape Cod Canal?
10. How does this compare to other bridge projects?

Why are the bridges being replaced?

The Bourne and Sagamore bridges have stood over the Cape Cod Canal since 1935. That makes them 90 years old.

When they were built, cars were small. There weren’t many of them. The bridges were designed for 1930s traffic.

Today is different. Big trucks cross the canal every day. Tens of thousands of cars use the bridges in summer. The bridges weren’t built for this much weight or this much traffic.

The U.S. Army Corps of Engineers, which owns the bridges, has patched them many times. These fixes cost more every year. The bridges are reaching the end of their life. Like an old car that needs more and more repairs, there’s a point where it makes more sense to replace than to patch.

The new bridges will also be wider. They’ll have more lanes for cars and trucks, safer paths for people walking and biking, and they’ll be tall enough that boats can still pass underneath, just like today.

When will the new bridges be ready?

About eleven years from now. Both should be done by 2037.

The bridges are the only way to drive onto the Cape. Workers can’t shut them down and start over. Cars and trucks need to keep moving the whole time. So workers will build a new bridge while the old one keeps working. When the new one opens, they tear down the old one. Then they do the same thing with the other bridge.

The Sagamore goes first. Construction starts in the winter of 2027 and 2028. The new southbound side opens in 2033. The new northbound side opens in 2036.

The Bourne follows about a year behind. Construction begins around 2029, with the same schedule shifted by a year.

Big milestones to watch:

• 2026: Permits done. The team that will build it is being chosen.
• 2028: First construction equipment arrives at the Sagamore.
• 2031: First piece of new bridge floats up the canal and is lifted into place.
• 2033: First new lanes open to traffic.
• 2037: All work done. Both new bridges in their final form.

What is a tied-arch bridge?

A tied-arch bridge has a big curved arch on top, like an upside-down U. The road hangs from the arch using thin steel cables.

Picture a rainbow with cars driving underneath. That’s the basic idea.

The arch is the strong part. It pushes down and out. The road below acts like a tie, pulling the arch ends back together. That’s where the name comes from. The arch is “tied” together by the road.

This shape is good for crossing wide rivers and canals. The arch doesn’t need supports in the middle of the water. That matters for the Cape Cod Canal, because boats need to pass through.

The new Bourne and Sagamore will both be tied-arch bridges. From the water, they’ll look modern and clean. From the road, drivers won’t notice much different from any other highway bridge.

How will workers build them?

Most bridges get built right where they will sit, one piece at a time, over many months. The Cape Cod Canal bridges will be built differently.

Workers will build the main spans (the long parts that cross the canal) at a shipyard somewhere else. The spans will sit on giant platforms, called barges. When each span is finished, the barges float it down the canal.

At the bridge site, cranes will lift the span off the barges and place it on top of the new piers. This is called a “float-in.”

The float-in for the new Sagamore southbound side is planned for 2031. The northbound side floats in around 2036.

Building the spans somewhere else first is faster and safer. Workers don’t have to spend years over the water dealing with traffic, weather and tides.

Will the bridges close during construction?

No. The bridges stay open the whole time.

Workers will build the new bridges next to the old ones, not on top of them. When a new bridge is ready, traffic moves to it. Then the old bridge is taken down.

Some short lane reductions are likely during construction, especially for maintenance windows. We cover those when they’re announced.

The first big traffic shift happens in fall 2033. That’s when the new southbound side of the Sagamore opens. Drivers cross on the new bridge. The old Sagamore comes down that winter.

The Bourne goes through the same process about a year later.

Who pays for it?

The total cost is $4.5 billion. That’s a lot of money, and it comes from a few places.

The federal government pays the biggest share. They committed $1.72 billion for the Sagamore.

The state of Massachusetts pays the next biggest share. The MassDOT spending plan from 2026 to 2030 includes $700 million for this project.

Together, federal and state money fully covers the $2.13 billion Sagamore replacement.

The Bourne replacement, at $2.37 billion, is not yet fully funded. The state is asking the federal government for more grant money. That funding is still being worked out.

None of the money comes out of local Cape budgets. This is a state and federal project.

What is eminent domain, and who is affected?

Eminent domain is when the government takes private land for public use. The owner is paid for the land, but they don’t always get to refuse the sale.

For the new Sagamore, MassDOT is taking 12 homes and 3 businesses. These properties are on land where the new ramps and approaches will be built.

The state has been working with property owners since 2025. By fall 2027, all property purchases should be done.

If you live near the bridges and haven’t been contacted, your land isn’t being taken. The footprint of the new bridges is mostly the same as the old ones, with small expansions only at specific spots.

What about people walking and biking?

Walkers and bikers get more space and safer paths.

The current bridges have narrow sidewalks. The Bourne sidewalk is one direction at a time when it’s open at all. Walking across is uncomfortable, especially in wind or rain.

The new bridges will have wide shared-use paths, separated from cars by a barrier. They’ll be wide enough for people walking, jogging, biking and using wheelchairs.

The paths will connect to the Cape Cod Canal trail on both sides. Eventually you’ll be able to bike from Falmouth to Sandwich on dedicated paths, including across the canal.

During construction, the existing sidewalks stay in service most of the time, with planned closures for short maintenance windows.

Why do we have the Cape Cod Canal?

The canal connects Buzzards Bay on the west to Cape Cod Bay on the east. It cuts across the base of the Cape, saving ships about 135 miles.

Before the canal, ships had to sail around the outer Cape. That route was long and dangerous. Hundreds of ships sank in the rough waters off Provincetown and Chatham over the years.

Construction of the canal started in 1909. It opened in 1914. It was widened and deepened in the 1930s, around the same time the current bridges were built.

The U.S. Army Corps of Engineers owns and operates the canal. They also own the bridges. Big tankers, fishing boats, ferries and pleasure boats all use the canal year-round. It’s free to use.

That’s why the bridges have to stay tall. Anything that lowered the clearance would block the canal for big ships.

How does this compare to other bridge projects?

The $4.5 billion Cape Cod project is big, but not the biggest in recent U.S. history.

For comparison: the Tappan Zee Bridge replacement in New York cost about $4 billion and took six years. The new San Francisco-Oakland Bay Bridge eastern span cost over $6 billion. The Verrazzano-Narrows rebuild in New York is in the same range as the Cape project.

What makes the Cape project unusual is that it’s two bridges, not one. And both have to keep working through eleven years of construction. That’s why it takes so long.

Compared to building a brand-new highway, replacing existing bridges in place is harder. There’s less room to work. Old utility lines run through the area. Traffic can’t stop. Workers and engineers earn that $4.5 billion.

This page is updated as the project moves forward. If something is unclear or missing, tell us.