Signs as deterrents of illegal parking in spaces designated for individuals with physical disabilities.

The percentage of illegal parking in spaces reserved for the physically disabled was monitored under three sign conditions: ground markings, ground markings plus vertical signs, and vertical signs containing a message that concerned citizens were watching the spaces. Illegal parking dropped from 69.3% of 102 vehicles during the initial ground-sign condition to 57.3% of 36 vehicles in the first vertical-sign condition. Following removal of the vertical signs, illegal parking increased to 68.7% of 43 vehicles. During the second vertical-sign condition, illegal parking dropped to 53.7% of 32 vehicles, followed by an increase to 69.5% of 68 vehicles after the vertical signs were removed. The lowest rate of illegal parking (27.1% of 78 vehicles) occurred in the vertical sign-plus-message condition. Illegal parking subsequently increased to 34.6% (of 94 vehicles) when the message sign was removed, followed by an increase to 65.2% (of 105 vehicles) when the vertical signs were removed.