Crashworthy Perforated Square Steel Tube (PSST) Mailbox Support – Phase II

Federal requirements have made it mandatory that safe mailbox support systems be designed to yield or breakaway when impacted by a vehicle. NDOT has previously used a non-proprietary, u-channel post mailbox support that was evaluated at MwRSF in the 1980's to NCHRP 230. This design was successfully evaluated to AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals (1985) with a small car vehicle in weak and strong soils as well as at 20 mph and 60 mph speeds. Single and double mailbox configurations were also evaluated. This design was implemented into NDOT’s standard plans. However, this standard plan is now obsolete. Very few mailbox supports have been evaluated according to MASH TL-3 specifications. The Texas A&M Transportation Institute (TTI) evaluated locking architectural mailboxes on thin-wall, steel-tube supports to MASH TL-3 (TTI Report No. 9-1002-12-9). A single-mailbox mount was tested and was successful. Two multiple-mailbox (combined standard and locking architectural mailboxes) mounts were tested and both configurations failed to meet MASH TL-3. The mailbox support for multiple mailboxes was subsequently redesigned and resulted in successful MASH TL-3 tests. Due to the limited number of tested mailbox supports, NDOT desired to design and evaluate a MASH TL-3 mailbox support.