Motorist Comprehension of Traffic Control Devices for Mobile Operations

In 2004, researchers conducted surveys to evaluate motorist comprehension of various mobile traffic control devices used to inform drivers about the number of vehicles in a work convoy; speed differential between the work convoy and the normal traffic stream; and passing a work convoy on two-lane, two-way roadways with improved shoulders. Four static signs were investigated to ascertain whether they inform motorists that they are approaching multiple work vehicles. Three of the signs (including the sign “Work Convoy”) had comprehension levels less than 53%. Placing the number of work vehicles on the sign (i.e., “3 Vehicle Convey”) improved the comprehension level to 79%. Various mobile speed displays were evaluated to determine if they provide information to motorists about the speed differential between the work convoy and approaching traffic. Only the “Your Speed” display (indicating speed of approaching vehicles) was understood by more than 85% of participants. In Texas, when mobile operations are conducted on the centerline of a two-lane, two-way roadway with improved shoulders, motorists are directed via a right flashing arrow panel to pass the work convoy to the right on the improved shoulder. However, under the current setup, only 66% of participants understood that they were supposed to pass the work vehicles on the right. All alternative text messages improved the comprehension rate; however, the “Pass on Shoulder” message was understood by the highest percentage of participants, at 97%.