In 2003, the Maryland State Highway Administration (SHA) developed a plan to install an automated fog-warning system in fog prone areas of I-68 near Big Savage Mountain. The warning system was designed to use existing environmental sensor station (ESS) visibility sensors and wireless communications equipment to activate flashers on roadside message signs during periods of limited visibility. Each sign had two flashing lights and a printed message displaying the text REDUCED VISIBILITY WHEN FLASHING.

This report provided a cost estimate to add fog warning systems to the existing ESS at Big Savage and Keysers Ridge, and one proposed ESS at Friendsville. Each warning system interfaced spread-spectrum wireless communications with an ESS contact enclosure. When fog was detected, the contact enclosure triggered a transmitter and activated the warning signs. The ESS sensor data, including surface, subsurface, and atmospheric data were sent to the central Road Weather Information System (RWIS) at the District-6 operations center via a telephone landline.

ESS site selection was dependent on the availability of utilities (telephone and power) in the area, the ability to collect representative environmental data, and the need to install line-of-sight wireless communications between ESS transmitters and the roadside warning signs. In areas where line-of-sight wireless communications were limited, signal repeaters were proposed.

The table below, excerpted from the report, provides a cost estimate to add a fog warning system to a previously installed ESS at Big Savage.

Quantity Description Unit Cost Extension LS Furnish and install “Scan Sentry Alarming and Alerting” software on the Disrict-6 central RWIS server   $5,000 LS Modify existing ESS (RWIS station) to provide contact closure under low visibility conditions   $2,500 1 Furnish and install radio transmitter, cabinet, and omni-directional antenna $5,000 $5,000 3 Furnish and install solar panel power system (repeater site and two warning signs) $7,500 $22,500 1 Furnish and install radio repeater with support pole and two Yagi directional antennas $7,000 $7,000 2 Furnish and install warning sign with LED’s and flasher and radio receiver with Yagi directional antenna $13,000 $26,000 LS Contingency $7,000 TOTAL     $75,000

The table below, excerpted from the report, provides a cost estimate to add a fog warning system to a previously installed ESS at Keysers Ridge.

Quantity	Description	Unit Cost	Extension
LS	Modify existing ESS (RWIS station) to provide contact closure under low visibility conditions	$2,500	$2,500
1	Furnish and install radio transmitter, cabinet, and omni-directional antenna	$5,000	$5,000
3	Furnish and install solar panel power system (three warning signs)	$7,500	$22,500
3	Furnish and install warning sign with LED’s and flasher and radio receiver with Yagi directional antennas	$13,000	$39,000
LS	Contingency		$6,000
TOTAL			$75,000

The table below, excerpted from the report, provided an estimate of the cost to install a new ESS (RWIS station) and fog warning system at Friendsville.

Quantity	Description	Unit Cost	Extension
LS	Furnish and install new ESS (RWIS station) that provides contact closure under low visibility conditions	$60,000	$60,000
1	Furnish and install radio transmitter, cabinet, and omni-directional antenna	$5,000	$5,000
2	Furnish and install solar panel power system (two warning signs)	$7,500	$15,000
2	Furnish and install warning sign with LED’s, flasher, and radio receiver with Yagi directional antenna.	$13,000	$26,000
LS	Electrical power and telephone connect		$5,000
LS	Contingency		$14,000
TOTAL			$125,000

Note: An environmental sensor station (ESS) is also referred to as a road weather information system (RWIS) station, or a weather station.
LS = Lump Sum

Notes:
Click here for image of an environmental sensor station near Big Savage.

Click here for image of a fog warning sign.