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Sensitivity Matrix

II(a) Wind - Summary

Asset Categories   Wind - Summary
Mode Sub-Mode Important Impact-Asset Relationships Threshold Mobile-Specific Detail Potential Indicators of Sensitivity
Bridges Bridge (Superstructure) Winds stress bridges with additional horizontal loading. Bridges are designed with a certain amount of wind loading accounted for in the structure design. [14] Strong winds create more powerful waves which can stress the bridge superstructure and substructure. [51] ASCE 7-05 recommends using a wind design speed between 130-150 mph for majority of Mobile County. Higher wind speeds are correlated with larger waves and, to a lesser extent, more frequent wave periods. The effect is continuous, so the threshold at which damage occurs depends on the elevation of the bridge deck and other conditions. [63] During Hurricane Katrina, strong winds helped break a 13,000 ton semi-submersible drilling platform free from its dry-dock moorings. The drilling platform collided into the Cochrane-Africatown bridge. [36] - Presence of operator houses with electrical and mechanical equipment
- Age
Bridge (Substructure) Strong winds create high flow velocities (including wave high wave impact energy), which can lead to bridge scour. [51] Higher wind speeds are correlated with higher kinetic energy of the water. The effect is continuous, so the threshold at which damage occurs depends on factors such as the substrate type, and the depth and geometry of footers. [63]    
Operator Houses (movable bridges) and electrical parts Wind damage to operator houses causes damage to the electrical and mechanical equipment of the bridge, and may exacerbate rain damage. [51] Higher wind speeds are correlated with larger waves and, to a lesser extent, more frequent wave periods. The effect is continuous, so the threshold at which damage occurs depends on the elevation of the bridge deck and other conditions. [63]    
Roads and Highways Paved road surface Wind does not directly damage the physical structure of the road, but can severely disrupt road traffic and other service activities. No documented relationship. No documented relationship. - Structure elevation
Road substructure (gravel base, substructure)  
Unpaved roads Wind can stir up dust from unpaved roads, causing eye irritation to residents and other health issues. [43] Moderate winds stir up dust from dirt roads, resulting in minor discomfort and damage.  
Stormwater drainage (culverts, side drains, etc) Wind damages trees, buildings, and other structures. Debris from this destruction can clog the stormwater drainage system, resulting in flooding impacts to the surrounding area. [43] Damage from wind creates debris, which can clog stormwater draining systems, exacerbating flooding damage.  
Highway, road and street signs and traffic lights Winds can blow over highway, street, and road signs. The Alabama AASHTO wind design speed is 140 mph. If street signs (such as stop signs) are not buried deeply in strong soils they may not be in compliance with design standard and may fail at (much) lower wind speeds. [40] During Hurricanes Katrina and Wilma, a large proportion of street signs failed in Miami-Dade county and the vicinity. The majority of these street signs failed at their foundations - mostly by leaning more than 15 degrees sideways or falling over completely. [40]
Highway and road traffic and service High winds cause safety risks and travel delays, a loss of visibility, impaired mobility, loss of communications and power, freight/cargo damage risk, increased risk of collisions/spills of hazardous cargo, and transport schedule delays. [49] Winds become dangerous to road maintenance, truck operations, and other road users at around 39 mph and are very dangerous at 74 mph. [49] AASHTO LRFD wind load provisions assume that no traffic will be present on a bridge when wind speed exceeds 56 mph. [73]  
Railroads Electrical Equipment (gates/flashers and signal bungalows) Intense crosswinds in some areas from microbursts or squall lines cut electricity needed for gates/flashers and signal bungalow operation. [57] Winds (head, cross, or tail) >= 50 mph [49] Mesoscale storms can occur in all geographic locations. In Mobile, in particular, there is the additional threat of high winds from tropical storms. [60]  
Railroad Tracks, Ties, and Ballast No documented relationship.      
Railroad services (i.e., operations) Intense crosswinds in some areas from microbursts or squall lines can disrupt or halt service.
There are potential safety risks to railroad personnel (such as from rail car blow over and hazardous spills), as well, which may disrupt operations. [49, 57]
Winds (head, cross, or tail) >= 50 mph [49]

The 3-second gust basic wind speed that is used to determine the pressures that buildings and other structures must withstand is 130 to 150 mph in the Mobile area. [66]
   
Airports/ Heliports Runway and navigational aids        
Aircraft Damage from lightning or hail storms on aircraft. [39, 49] Hail greater than 1 inch can severely damage aircraft; hail storms within 5 nautical miles of airfield. [49] No documented relationship.  
Airfield buildings and structures (e.g., terminal buildings, hangers, air traffic control tower) High winds, storms can cause damage to terminal buildings at airports.
High winds can cause construction materials to blow loose, placing debris and objects in the pathways of moving aircraft. [6, 49, 64]
Impacts can occur at wind speeds of greater than 25 to 35 knots. [49]
The 3-second gust basic wind speed that is used to determine the pressures that buildings and other structures must withstand according to ASCE 7-05 is 120 to 150 mph in the Mobile area. [66]
Mobile Downtown Airport: Mobile Downtown Airport closes for two days at a time during hurricanes, typically two times per year
Mobile Regional Airport: Mobile Regional Airport closes for two days at a time during hurricanes, typically two times per year. [64]
- Strength and redundancy of terminals, equipment, signage [6]
Services and airport/ heliport operations (e.g., flight departures and arrivals, baggage/cargo transfers, ground transportation) Thunderstorms can increase the likelihood of delays
High winds increase the likelihood of flight delays
Poor visibility in storms, weather can increase the likelihood of delays
Storms, high winds with cross wind components can cause delays [39, 53, 49, 60, 64]
Maximum cross-wind (i.e., the speed of the 90-degree component of wind velocity) under which landing is allowed by FAA guidelines is 23 mph or 20% of a plane's stall speed during landing.
Cross-wind limit for most small planes is 23 mph; flight crew manual for Boeing 757/767 recommends landing cross-wind limits of 46 mph in dry and wet conditions, 23 mph in standing water or slush, and 20 mph on iced runways.
Wind speeds greater than 29 to 40 mph [16, 53, 12, 49]
Storms may also disrupt access to other transportation systems, such as local ground transportation.
Rerouting and diversions can result in "excess operating costs and lost passenger time".
Mobile-area airports' runways are aligned into wind flow; secondary runways at Downtown and Regional airports provide relief in crosswinds. [53, 39, 64]
- Extent to which secondary runways can provide relief during high crosswinds.
Natural Oil and Gas Pipelines Pipelines, aboveground Strong winds can uproot trees and cause other debris-related damages to gas mains, services, meters and aboveground piping. Offices and equipment storage facilities also experienced wind-related damage. [59] Wind speeds above 60 mph can damage pipeline systems. [49] During Hurricane Frederic, underground and aboveground piping, systems, and meters sustained damage. [59]  
Pipelines, underground No documented relationship. No documented relationship. No documented relationship. No documented relationship.
Pipelines, offshore No documented relationship. No documented relationship. No documented relationship. No documented relationship.
Aboveground infrastructure (e.g., compressor stations, metering stations, other buildings, structures) High winds can damage gasoline supply stations; canopies at gas pumping stations may be particularly vulnerable. [56] The 3-second gust basic wind speed that is used to determine the pressures that buildings and other structures must withstand according to ASCE 7-05 is 120 to 150 mph in the Mobile area. [66]   - Canopies at fuel pumping stations may be susceptible to high winds, becoming airborne and damaging pumps or other nearby equipment. [56]
Utilities for pipelines - electricity See "Electric Power Systems". See "Electric Power Systems". See "Electric Power Systems". See "Electric Power Systems".
Electric Power Systems Electric Power Systems Winds in strong, powerful storms can cause electricity outages, while in weaker storms, damage is caused more by flooding or thunderstorms than strong winds. Wind (both gusts and average wind speed) can damage power lines and knock trees into power lines. In wind, pole may be directly upended, but most of the impacts seem to be from snapping of trees and branches which then fall on power lines to cause outages. [35] Wind speeds above 20 meters per second, or 72 kilometers per hour (45 miles per hour).
Line failures and outages, have been observed at wind speeds of 40 to 56 mph, which is one-third to one-half of the 2-minute sustained wind speed using ASCE 7-05. The maximum 3-second gust basic wind speed for the Mobile area is 150 mph, which is equivalent to a 2-minute sustained wind speed of 114 mph (183 km/h). [35, 56]
During Hurricane Frederic, Mobile County sustained large amounts of wind-related damage to its electric utility system. [59] - Above-ground infrastructure is more susceptible to damage during storms. However, "hardening" infrastructure by moving above-ground infrastructure under-ground is very expensive. It may be better to address outages through planning and response to outages (e.g., tree trimming, maintenance of poles may be an effective strategies)
- A greater number of overhead power system components such as transformers, switches, miles of overhead cable, in a given area will lead to longer power outages during or after storm events.
- Damage that occurs to stations, poles, lines in hard to access areas (e.g., wet or flooded areas, marshes, areas without road access) can lead to prolonged outages.
- Simultaneous damage to north-south and east-west lines can make rerouting of power delivery extremely difficult and reduce the resiliency of the system.
- Both steel and wooden towers are susceptible to high winds; wooden towers appeared to fail at or near the base, while steel towers experienced buckling of critical members [26, 35, 55, 56]
Marine Ports, Terminals, and Waterways Electrical Equipment Equipment left out at risk. Equipment in damaged buildings at risk. [48]      
Terminal Buildings Wind damage to structures increases non-linearly as wind speed increases. For example, Powell et al. (2007) found that light, moderate, and severe wind damage thresholds correspond to loss levels of around 2%, 12%, and 60% of insured value. Furthermore, winds greater than or equal to 55 m/s produced about 30 times more loss than winds from 25 to 41 m/s. [76] The 3-second gust basic wind speed that is used to determine the pressures that buildings and other structures must withstand according to ASCE 7-05 is 120 to 150 mph in the Mobile area. [66] During Hurricane Katrina, wind damage was relatively minor and was primarily confined to warehouse sheet metal cladding. Most ports/piers built to withstand high winds. [2]  
Channels Debris from high winds. [48]      
Piers, wharves, and berths No documented relationship. Floating piers and dry docks are often designed for winds with a 100 year return period. [32]    
Port services (i.e., operations) Disruptions due to storms or evacuations. Small boat handling, ferry docking, barge handling all restricted. [48, 49] Berthing of large vessels is affected when winds exceed ~23 mph. High-speed ferries may continue to operate in winds up to ~46 mph. Container and gantry-type cranes are generally affected with sustained wind speeds exceeding ~29 mph. Design standards assume that larger vessels will vacate their berth when winds exceed around 58-69 mph. [32]    

*Note dollar amounts are not adjusted for inflation.

 

Updated: 03/27/2014
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