Attainable Vehicle Speed. Vehicle speed at the point of impact is a major parameter in
determining the required performance of a vehicle barrier. The impact is calculated from the initial
speed, "v," the acceleration rate, "a," and the distance, "s," available for acceleration between the
starting point and the point of impact. Surface condition of the path, the general terrain, whether the
path is straight or curved, and if curved, whether or not it is banked, are additional factors that must
be considered. Information presented in Figures 5 through 9 may be used to either calculate the
maximum attainable vehicle speed, or to suggest strategies for modifying possible attacking paths
for vehicle speed control.
Based on topographical descriptions, all possible driving paths should be identified on
the map so the impact speed along the perimeter can be calculated. Using this data, the strategy for
barrier design, selection, and installation can then be developed.
NOTE: The typical acceleration of conventional vehicles is usually known. For
example, 11.3 feet per second squared (3.45 meters per second squared) is typical for high
performance cars, and 5.8 feet per second squared (1.77 meters per second squared) is typical for 2-
1/2-ton (2,273-kg) commercial trucks.
Attainable Vehicle Speed on a Straight Path. A long, straight path between the starting
point and a vehicle barrier will result in the highest attainable vehicle speed.
a) On a Horizontal Surface. On a horizontal, straight path, the speed attainable by an
accelerating vehicle depends primarily on its initial speed, "v0," the acceleration, "a," and the
distance, "s," traveled during acceleration. The relationship among these parameters is given in
v 2 = v 2 + 2as
final vehicle speed
initial vehicle speed
For convenience, Equation (1) is plotted as Figure 5, using a conversion factor for values
in ft/sec and mph.