Tracking windy conditions
Strong winds from hurricanes rolling up the East Coast pose danger for motorists crossing bridges in Maryland. Sustained winds higher than 50 miles per hour can toss around large trucks and other vehicles driving on long spans high above the state’s waterways. To protect drivers from strong winds, last summer the Maryland State Highway Administration (SHA) installed wireless wind measurement systems on two bridges to alert officials to dangerous conditions that may warrant their temporary closure.
Motorists on the Severn River Bridge and the Thomas Johnson Bridge, which spans the Patuxent River, frequently battle strong gusts and sustained winds during hurricanes. In 2003 a strong gust blew an empty box truck into a parapet on the Severn River Bridge. “The approaches to that bridge are in cuts,” says Greg Welker, District 5 engineer for SHA. “You have hills on each side, so you’re driving with no wind on you and all of a sudden, the wind hits your vehicle.”
Anemometers mounted to a weather station on the banks of the Severn River were shielded by trees and could not accurately measure the wind on the bridge. During hurricanes, SHA employees would drive a dump truck onto the bridge and measure the wind with a hand-held anemometer. If winds were strong enough, SHA would close the bridge. “You had to have someone staying down there all the time, and maybe we were exposing them to some hazards we didn’t need to,” Welker says. “We had been using a seat-of-the-pants method to decide when to close the bridge.”
SHA officials took closing cues from the Maryland Transportation Authority, which operates the William Preston Lane Jr. Memorial Bridge, crossing the Chesapeake Bay. SHA officials also used weather information from bay buoys, which were destroyed when Hurricane Isabel hit Maryland in 2003.
SHA Communications Division Chief Craig Fetzer turned to the manufacturer of the existing bridge weather stations, St. Louis-based Surface Systems Inc. (SSI), to help design a system that would secure an anemometer at a bridge’s midpoint and send the wind data wirelessly to the weather station on the river bank. Because the bridges do not have a conduit in which to run electricity or telephone wires, the units needed to be solar powered with a battery back up.
Project construction began in May 2004 and was complete on both bridges one month later. Locally based Transys Services installed the equipment. Including engineering, the project cost $46,000 for both bridges.
Now, SHA officials can monitor the bridges’ wind conditions through Web browsers in the central control office that display information collected at the weather stations. If power fails, SHA staff can drive to the bridge and collect the anemometer data on land with hand-held computers. A magnetic antenna attached to a vehicle’s roof registers the radio signals, and wind speed and direction display on handhelds. “If we’re within two miles of the bridge with the vehicle, it will automatically display in real time what the speed and direction is of the wind. If the operations center goes down, and we can’t collect it, we can still collect it when we go out there to close the bridge down,” Fetzer says.
SHA officials assembled a task force of city and county officials as well as staff from the Naval Air Station to formulate a policy for closing the bridges. Under the worst storm conditions, all vehicles except emergency responders will be directed to detour around the bridges.
The equipment has been working as planned since installation, but the real tests are expected during this year’s hurricane season. The National Oceanic and Atmospheric Administration predicts that 12 to 15 tropical storms and seven to nine hurricanes will crop up in the Atlantic Ocean in 2005.