Focus On Intersections
To meet MASH criteria, sign structures must meet certain guidelines based on different impact conditions, including vehicle, speed, and angle of impact.
Questions
- Why are intersections important and how are they so different than a mainline roadway, when it comes to signing / sign structures?
- Why isn’t a 65mph impact along a mainline roadway potentially more dangerous than a 25mph impact at an intersection?
Answers
To get a good understanding of the implications of those two points listed above, we first must understand the dynamic of the traffic in those two areas. On a mainline roadway/highway, traffic is generally traveling in exactly the same direction at approximately the same speed. An impact to a roadside sign occurs when a vehicle leaves the roadway and travels toward the sign. Typically that type of impact is nearly at a 0˚ impact. The sign structure must breakaway per MASH criteria and is not allowed to incur excessive damage to various parts of the vehicle (or occupants), again per MASH criteria.
If only the MASH test matrix is used for that type of impact then that assembly would ONLY be MASH Compliant on mainline roadways. An intersecting roadway is very different. You may have traffic that is stopped, or traffic that is traveling at a much higher speed than other traffic. There are many types of intersecting or crossover roadways. Some are at 90˚ angles from each other and others are at only slight angles. The MASH document states that any sign assembly/structure that is used at an intersecting roadway must not only have been tested at the angle determined as worse case, but also must be tested at a 90˚ angle since they can be impacted from that angle at an intersecting road. So a sign assembly / structure must have at least 6 successful tests (3 frontal impacts and 3 side impacts) in order to be considered MASH compliant for intersecting roadways.