One Road Out: Bridge and Causeway Closure Thresholds, and How to Find Yours Before the Season

There is no national number for when a bridge or causeway closes in high wind. Each structure’s authority sets its own rule, and the rules differ in the number, in how wind is measured and in whether “closed” means closed at all. If one bridge is the only way off the ground your animals live on, find your structure’s rule before the season, then treat it as your departure deadline.

That deadline is not the National Weather Service’s, and it is not the county’s evacuation order. It is the moment the structure stops carrying traffic, set by whichever agency maintains and polices that span. With one road out, departure is a capacity call before it is a weather call, because there is no second trip.

The number people repeat is 40 mph. It has real backing in specific places, and it is not a national rule. A lookup table would mislead you, so this page shows how the rules differ and then walks you through getting the number that governs your household.

Four Florida authorities, four answers

Walton County Emergency Management answers for a named structure. Its hurricane FAQ says: “The bridge is closed at sustained 40 MPH winds.” That is the Clyde B. Wells (US 331) Bridge. The same page says closure decisions are made by FDOT, the Florida Highway Patrol and local law enforcement based on current conditions, and that conditions can change with little or no warning that the bridge will close. The FAQ is a live storm-status page, so take the rule from it, not the status.

Pinellas County, in an October 8, 2024 notice ahead of Hurricane Milton, said the Florida Highway Patrol and FDOT will close the Sunshine Skyway bridge when wind speeds reach about 45 mph. It said the Gandy Bridge, Howard Frankland Bridge and Courtney Campbell Causeway will be closed if wave action makes travel unsafe. Those three crossings get no wind number. A household planning around 40 mph and crossing the Courtney Campbell Causeway is planning against a rule that does not apply to it. The same notice covered a separate mechanism: three movable bridges were to be locked closed to boat traffic at noon that day while staying open to vehicles.

FDOT, in its statewide update of August 5, 2024 during Hurricane Debby, described a practice, not a trigger: “Once wind speeds increase beyond 40 mph, FHP may deem it necessary for closure.” Law enforcement then stops traffic from crossing. The sentence says “may,” and it does not say sustained or gust.

Lee County Emergency Management goes furthest. Its one-page document, last revised July 2021, says the county cannot literally close bridges during tropical storms or hurricanes. It advises drivers to stay off bridges, and off the roads leading to them, when sustained winds reach 40 mph (tropical storm force). Its reasons:

• Gusts can already be much higher at that speed.
• Winds are stronger at higher elevations, so danger rises on higher bridges and elevated roadways.
• Barricades, cones, gates and signs can blow away, so the county does not use them, and it does not post officers on bridges.
• Emergency responders (fire, police, ambulance, tow trucks) cannot respond during tropical-storm-force winds, so a crash, or even a flat tire, becomes a life-threatening event on a bridge.

So one state gives you a hard sustained number for one bridge, a different number for another plus a wave-action rule for three more, a discretionary statewide practice, and a county that closes nothing and only advises.

Other states change the shape of the rule

Chesapeake Bay Bridge-Tunnel: four levels and an averaging basis

The Chesapeake Bay Bridge-Tunnel (CBBT) policy, effective July 1, 2022, heads its table “Average Wind Speed (mph).” That is neither the sustained figure Florida counties use nor the gust figure on a phone weather app. The bands, which the facility’s live weather page repeats:

• Advisory, 35 mph: speed limit reduced to 45 mph and no passing.
• Level 1, 40 mph: vehicles not allowed to cross include motorcycles, large pick-up campers, camper trailers, house trailers and anything being towed.
• Level 2, 50 mph: only cars without exterior cargo, pick-up trucks without cargo, mini-vans, vans that are not high-profile or conversion vans, and SUVs may cross.
• Level 3, 60+ mph: closed to all traffic for weather or safety.

If you tow a trailer, camper or horse rig, your cutoff on this facility is 40 mph, not 60. The weather page also warns that these restrictions may change at any time.

Maryland Transportation Authority: sustained wind and gusts, each with a clock

The Maryland Transportation Authority (MDTA) defines each band by a duration. The same bands appear on a 2015 MDTA news post (updated 5/18/15) and on the maintained Bay Bridge emergency-closures page, which is the one to bookmark. The age of the post is a reason to confirm by phone, not to discount the numbers.

• Wind Warnings: sustained 30–39 mph for 10 continuous minutes or more, or gusts persistently above 30 mph over 15 minutes. Drivers of house trailers, box trailers, motorcycles and vehicles with cargo on roof racks are advised to use caution.
• Limited Wind Restrictions: sustained 40–49 mph for 10 minutes or more, or gusts persistently above 40 mph over 15 minutes. House trailers, empty box trailers and any vehicle that law-enforcement personnel judge unable to cross safely are prohibited, and turned-away drivers are helped to turn around.
• Full Wind Restrictions: sustained above 50 mph for 10 minutes or more, or gusts persistently above 50 mph over 15 minutes. Only automobiles, pickup trucks, flatbed trailers, commercial buses and heavy-laden tractor-trailers may cross.
• Traffic Holds/Bridge Closure: sustained above 55 mph for 10 minutes or more, or gusts persistently above 55 mph over 15 minutes. On a sudden increase that could jeopardize life or property, MDTA may stop all traffic.

At 40 mph an MDTA bridge is not closed. That band takes off trailers and lets an officer turn away any vehicle. The closure band has a numeric trigger at 55 and a separate discretionary clause, so the number is the floor of the decision, not the whole of it. The maintained page adds that when a wind warning, restriction or closure is in effect at the Thomas J. Hatem Memorial Bridge (US 40), no bicycles are permitted.

Mackinac Bridge Authority: sustained only, and a gauge on the bridge

On a Michigan DOT FAQ page, the Mackinac Bridge Authority states: “These speeds are not for gusts; they are sustained winds from any direction.” It adds that these are minimum conditions, and that restrictions may be put in place at lower speeds if other hazardous conditions are present. Its bands:

• 0–20 mph: no restrictions; the bridge speed limit is 45 mph.
• 20–35 mph: high wind advisory.
• 35–50 mph: mandatory escorts for high-profile vehicles.
• 50–65 mph: closed to high-profile vehicles. Passenger vehicles that are not towing may cross at no more than 20 mph.
• 65 mph and above: closed to all traffic.

The authority says it uses wind gauges on the bridge to decide advisories and closures, which answers where the wind is read. Wind closures are not only a hurricane topic: this bridge closes for wind, at a figure 25 mph above the Walton County number.

A 2013 multi-state survey said the same thing

The I-95 Corridor Coalition surveyed its sixteen member states and published the results in September 2013. Its state figures are now thirteen years old. Its headline finding: over half of the states close bridges at certain sustained wind speeds, and those thresholds vary from 39 to 80 mph and are used as guidelines. The exceptions it lists are Vermont, New Hampshire, Connecticut, Pennsylvania, New Jersey/non-metro New York City, North Carolina and Georgia. Other findings:

• Apart from two sub-regions within two states, no state provided an official documented policy for highway and bridge closures.
• All states except Maryland and Georgia said closure triggers are guidelines, not an automatic hard closure.
• All state law enforcement agencies have legal authority to close highways and bridges to all traffic.
• Reported figures: South Carolina, Virginia and Florida close bridges at 39–45 mph; Delaware and Maryland at 50–55 mph, with some New York bridges closing to all traffic at 50 mph; Rhode Island and New York close most bridges at 60–65 mph; Maine at 80 mph. Massachusetts closes at 39–45 mph when other conditions such as snow, ice or driving rain are present.

Two cautions. These are 2013 self-reports by states, and some may have changed. And a state-level figure is not a structure-level rule: the survey’s Virginia row is 39–45 mph, while the CBBT’s own policy sets Level 3 closure at 60+ average wind. Do not treat a 2013 row as your bridge’s current rule.

The measurement basis is half the threshold

Authority	Structure or scope	Published closure basis
Walton County (FL) EM	Clyde B. Wells (US 331) Bridge	Sustained 40 mph, no duration stated
Pinellas County (FL)	Sunshine Skyway	About 45 mph, measure not stated
Pinellas County (FL)	Gandy, Howard Frankland, Courtney Campbell	Wave action making travel unsafe, no wind figure
FDOT (statewide practice)	Bridges in the impact area	Beyond 40 mph, FHP may decide; measure not stated
Lee County (FL) EM	County bridges	No closure mechanism; advisory at sustained 40 mph
Chesapeake Bay Bridge-Tunnel	The facility	Average wind speed, 60+ for Level 3 closure
Maryland Transportation Authority	MDTA bridges	Sustained over 55 for 10+ minutes, or gusts over 55 across 15 minutes
Mackinac Bridge Authority	Mackinac Bridge	Sustained from any direction, 65 mph and above, explicitly not gusts

Four bases appear in these rows: sustained wind with no duration, sustained wind with a stated duration, an average, and a non-wind criterion. A forecast of sustained 45 mph means different things depending on which row governs your road.

The forecast you see adds another mismatch. NOAA’s National Hurricane Center defines the sustained wind it reports as the highest one-minute average at 10 meters with unobstructed exposure, and puts tropical storm force at 34 kt (39 mph or 63 km/hr) on that one-minute average. MDTA uses a 10-minute continuous window, the CBBT sheet says average, and Mackinac reads gauges on the bridge. Lee County notes that winds are stronger at higher elevations. Ask your authority which measure it uses and how it compares with the forecast you will be watching.

Find your own structure’s rule before the season

Do this in the spring, before the season.

1. Name the structure exactly. Not “the bridge” and not the road number. Adjacent structures on the same highway can sit under different authorities.

2. Find who owns it and who maintains it. They can be different agencies. FHWA’s Specifications for the National Bridge Inventory (FHWA-HIF-22-017, March 2022) keeps them as separate fields: Item B.CL.01 is Owner, and Item B.CL.02 is the agency with primary maintenance responsibility. FHWA’s InfoBridge tool looks up the record for public highway bridges. The agency may be a state DOT, a county, a city, or an independent bridge or turnpike authority.

The record also carries Item B.CL.06, Emergency Evacuation Designation, which records whether the route on the bridge is an emergency evacuation route. FHWA’s commentary says to refer to the State Emergency Management Agency for designated evacuation routes.

3. Find out who makes the call. The maintainer may not be the closer. The 2013 survey says all state law enforcement agencies can close bridges, and Walton County names FDOT, the Florida Highway Patrol and local law enforcement together. Ask the maintaining agency who decides for your span.

4. Ask six questions, in writing, and keep the answers.

• What is the threshold at which this structure closes to ordinary passenger vehicles?
• Is it sustained wind or gusts?
• Over what averaging or duration period is it measured?
• Where is the wind measured, and can I see that reading in real time?
• Who makes the final decision, and does anyone else have to approve it?
• On which channel is the closure announced, and how far ahead?

5. Establish the restriction bands, not just the closure. If you tow, your effective cutoff is the first band that excludes your rig. On the CBBT, Level 1 at 40 mph excludes anything being towed. On MDTA bridges, the 40–49 mph band names house trailers and empty box trailers, and leaves other vehicles to an officer’s judgment; the band above 50 mph permits only the listed vehicle types. Ask your authority whether its band is a vehicle-type list or a list plus discretion. If you move large animals, read this with our guide to loading and moving horses and other large animals before a storm, because a trailer restriction can bite before any wind advisory affects a car.

6. Subscribe to the right channel now. The 2013 survey found that the vast majority of states use 511 and variable message signs to notify travelers of closures. Independent authorities often run their own feeds. The Greater New Orleans Expressway Commission, which operates the Lake Pontchartrain Causeway, tells users to check its social accounts, sign up for text or email advisories, or “tune into 1700 AM Radio to hear up to date information about the bridge.” A yellow banner appears on its website when an advisory is in effect. The commission’s home page lists these channels and gives no wind threshold, which is why step 4 is a phone call rather than a web search. Pair your channel with the tools in our guide to watching your evacuation route change in real time.

Work backward from the cutoff

Once you have a threshold with a basis attached, you can turn a wind number into a departure time.

The National Hurricane Center publishes an Arrival Time of Tropical-Storm-Force Winds graphic in two versions. It explains the reason: emergency managers use the arrival time to decide when to begin and complete coastal evacuations, and “Once sustained tropical-storm-force winds begin, such preparations usually become too dangerous or difficult.”

The version to use is the Earliest Reasonable Arrival Time. It is the time before which there is “no more than a 1-in-10 (10 percent) chance of seeing the onset of sustained tropical-storm-force winds.” NHC says it is the period during which preparations should ideally be completed for those with a low tolerance for risk. It contrasts it with a version for people willing to risk not finishing preparations. A household that cannot make a second trip for its animals is not that user. NHC adds that decision makers have historically read its products as fixed times, without allowing for track or size uncertainty, so communities may get less time if a storm speeds up or grows.

If your authority’s threshold is near tropical-storm force (39 mph on a one-minute average), that graphic is the right clock. Confirm first that your authority’s measure is comparable, because a 10-minute MDTA window and a one-minute NHC average are not interchangeable. If they are not comparable, ask which forecast product the authority watches.

Then subtract, in this order, using real numbers from your own household:

• Capture. The time to have every animal in hand. It has the widest variance and the least control, so budget from your worst rehearsal, not your best. Our guide to getting a hiding or panicking cat contained covers the emergency version of that job.
• Loading. Getting containers into the vehicle in an order that holds. Our guide to how carriers and crates go into a vehicle when there are several animals covers restraint and airflow.
• The drive to the structure. The leg that ends on the far side of the span, not the drive to your destination.
• The queue. On a single egress everyone uses the same road at the same time. Our guide to what happens to pets when the traffic stops moving covers the risks of a stopped vehicle.

Earliest Reasonable Arrival Time for tropical-storm-force winds at my location, from the current NHC graphic minus my rehearsed capture time for every animal minus my rehearsed load time for the containers in the order they go in minus the measured drive from my driveway to the far side of the structure minus my own queue allowance for a single egress = the hour I leave.

Only the first line comes from NHC, on the day. The other four come from a stopwatch in the spring, and no one else can supply them.

The result sits inside the watch-and-warning window in our hurricane playbook for pet households. Our guide to how early to leave with pets runs the same subtraction against a county’s clearance time. Your deadline is whichever comes first.

Why the single trip is not negotiable

On an ordinary evacuation, a household that misloads can turn around and come back. Across a structure with a closure threshold, the first trip is the only trip, so decide who and what is in it before you reach the driveway.

• Vehicle capacity. How many animals your vehicle holds, safely restrained, in one load is the whole answer. Work it out with a tape measure using our guide to how many animals fit in one vehicle.
• One convoy, not two cars. If a household splits across two cars and the cutoff lands between them, one driver is across and one is not, with the animals divided. Depart together.
• Boarding. If the honest arithmetic says you cannot capture, load and cross before the threshold, decide in advance where the animals go instead, and book it while capacity exists. See choosing between boarding and taking them with you.
• Slow-loading animals. A senior or mobility-limited animal, or one that must be lifted, adds minutes at the wrong moment; see moving an older or disabled animal in an evacuation. For several cats, see getting several cats out at once, because capture time does not scale in a straight line with the number of animals.

None of this changes whether you should leave, which is a separate decision covered in choosing between sheltering in place and evacuating. It changes the latest moment at which leaving is physically possible.

The second closure: after the storm

A structure that has taken a storm reopens after it is inspected and, if damaged, repaired. Those outcomes are separated by more than an order of magnitude in time.

Inspection can be fast. After Hurricane Idalia, FDOT reported that over 100 bridge inspectors were deployed, clearing over 1,000 bridges through the main impacted areas, and that “Less than 18 hours after the storm hit Florida, all state-owned bridge assessments had been completed.” In its August 5, 2024 Hurricane Debby update, FDOT said 120 bridge inspectors were on standby to deploy and crews were staged to inspect coastal bridges.

Repair is not fast. FDOT announced on October 19, 2022 that emergency repairs to the Sanibel Causeway after Hurricane Ian were completed in 15 days, more than a week ahead of schedule. FDOT’s secretary said the bridges were largely undamaged, but portions of the causeway that connect the bridge structures together were washed away, leaving the bridges unconnected to the mainland or the island. FDOT’s secretary said: “A project like this, under normal circumstances, could take months.” FDOT described the effort as restoring drivable access for the over 6,000 residents of Sanibel Island.

FDOT’s release also named a handoff: “Access to Sanibel Island via the Sanibel Causeway will be managed by Lee County.” A passable structure and permission to pass are two gates run by two agencies. Our guide to reaching a pet inside a closed zone covers the credential side.

If you evacuate across a single structure, assume you may be away for days or weeks, on a timeline set by an engineering assessment you cannot influence, and that anything left behind is on its own for that period. That is an argument for taking the animals. Where that is impossible, read our guide to what the law says about leaving an animal behind before you decide at speed. If an animal is separated from you, see finding an animal separated from you after a disaster.

Pre-season worksheet

Copy these into your evacuation plan and fill them in once, before a storm is named. Every blank is a question only your own authority can answer.

• Official name of my structure:
• Owner and maintenance-responsibility agencies, per the National Bridge Inventory:
• Agency that makes the closure decision:
• Law-enforcement agency that enforces it:
• Closure threshold for passenger cars:
• Sustained, gust, or average:
• Duration or averaging window:
• Where the wind is measured:
• The band at which towing is prohibited (if I tow):
• Announcement channel, and how I subscribed to it:
• Phone number for the authority’s traffic or operations line:
• Second structure or route, if one exists, and its separate threshold:
• My household’s honest capture-plus-load time, from a timed rehearsal:
• My leave-by time when the Earliest Reasonable Arrival graphic shows tropical-storm-force winds at hour X:
• Who is on the animals’ side of the structure if I am not:

The last line matters most on a weekday. If work, school runs or errands put a closable structure between you and your animals, the plan needs a named person with keys, written authority and a rehearsed destination. See getting an animal out when the order lands while you are at work. The same problem arises when the animal is at a kennel or clinic on the far side: see what happens when your pet is at a facility and the order hits.

What this page does not claim

This page is not a national table and cannot tell you your structure’s number. Three limits:

• The I-95 Corridor Coalition figures are from September 2013 and are the states’ own reports at that time. States may have revised their guidelines since.
• The Walton County answer sits on a live storm-status page with no revision stamp. Treat the rule as current and the surrounding status as a snapshot.
• The Lee County document was last revised in July 2021 and is still linked from the county’s hurricane index, but a county can change its posture without changing a PDF.

The only number that governs your evacuation is the one you get from the agency that closes your road. Get it before the season, not during a storm.

Where to go next

• The full hurricane playbook for pet households sets the watch-and-warning stages this cutoff sits inside.
• How early to leave with pets runs the same subtraction against your county’s published clearance time; whichever deadline is earlier governs.
• The T-minus storm countdown card is where a structure’s cutoff goes once you have the number.
• What happens to animals once the traffic stops moving picks up where this page ends.
• Reaching a pet inside a closed zone covers the credential gate that follows the engineering one.
• How carriers and crates load into one vehicle is the plan this deadline is applied to.
• The hazard playbook hub collects the rest of the storm, fire and flood guidance for animal households.