The gantry and roadway are laden with technology - radio devices to pick up signals from transponders, cameras to record license plates at high speeds, sensors to count vehicle axles - that may be critical to the nation's transportation future. Each time a vehicle passes under the gantry, with no need to slow down or stop, a purple light flashes to signal that a simulated toll has been collected.
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(Maryland) Finding funds in tolls and taxes 
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