The objective of the present study was to determine if the head of an unrestrained passenger would hit the windshield with a velocity that would cause injury should the automobile lose control and crash into a larger, so-called, "piggy-back" steel channel sign support used for intermediate size sign markers in the State of Ohio. First, the safe limits for impact velocities of the human head into automobile windshilds were established from literature on windshield safety and were found to be about 13 mph for pre-1966 model automobiles, and between 25 and 30 mph for 1966 and later model automobiles. Following, nine field tests were conducted to correlate the recording sensitivities of the servo and strain gage type accelerometers and then the data from each field test from a previous study were re-analyzed to obtain the potential passenger's head into windshield impact velocities. Finally, the results on head impact velocities were compared to the safe limits. The maximum value of head impact velocities were compared to the safe limits. The maximum value of head impact velocity from all tests was 14.1 mph, which was well within the safe limits for passengers in 1966 and later model automobiles, but was found to be unsafe, or at the best marginal, for passengers who may be traveling in pre-1966 model vehicles. /FHWA/