Originally posted at: www.slowstop.com
We're often asked if we have any recommendations for bollard spacing. Obviously this is a complicated question, as it depends on numerous factors, such as where the bollards are used, for what purpose, and what is the expected traffic around the bollard. In this article I won't discuss security rated bollards, because I believe this is a science to itself that requires careful engineering and is not appropriate for a blog post.
The most important consideration for most other application will be whether or not pedestrian traffic is expected in the area, and whether or not the area is a potential emergency exit route. The Americans with Disabilities Act often conflicts with the desired safety and security needs of the bollard spacing designer. Spacing of bollards in any area where pedestrians might need to traverse needs to be a minimum of three feet to allow for wheelchair ingress and egress. Four feet apart is a more common practice to allow extra clearance. Remember to consider any objects that extend from the bollard, especially with some architectural, removable, and lighted bollards. The three foot minimum should be between the farthest extensions of the bollard.
When protecting a utility or other object that does not require pedestrian egress, spacing can be much closer if desired. This usually depends on the expected mass and speed of vehicles travelling in an area when compared to the strength of the bollard. Here your most important consideration is speed of the vehicle. Remember that energy is function of mass times speed squared, meaning that as speed increases, energy increases rapidly. Spacing bollards tighter together, or even connecting them with cross bars, will increase the strength of the barrier. As a rule of thumb, if the spacing between the bollards is less than twice the impact height on the bollard, strength of the bollards will double when impacted together.
An common application of this principle is the horseshoe or u-bollard, most often seen protecting fuel pumping stations. A typical automobile vehicle bumper height is in the range of 17"-19". Given this, in order to double the strength of the bollard, the two vertical elements should be placed roughly 34"-38" apart. Of course the size of the fuel pumping island will impact whether or not this is feasible.
If automobile traffic is your main consideration, bollard spacing should be no more that five feet apart. Even the smallest automobiles available will be prevented from entering at this spacing. If fork lift or other industrial vehicles are the vehicles to be denied access, consider the width of the thinnest vehicle to be stopped and ensure that your bollard spacing is tighter than that vehicles' width.
Loading docks often use bollards to prevent trucks from impacting the building outside of the loading dock bumpers. Standard US bays have bumper plates that have an outside dimension of 96". This matches the outside width of most trailers and shipping containers. Give a 6" gap on either side and space loading dock bollards 9' apart (inside dimension). One special type of bollard, the rebounding bollard, can often be used to act as a bumper due to the fact that it gives upon impact, slowing the truck into postion.
As a final note, you should also consider the need to allow emergency vehicle access to an area. If this is required, you may need to have at least on area with a wide spacing, or at a minimum, a removable bollard that can be quickly removed in order to allow for emergency access to an area.
