As part of the re-design of the TL-3 system it was crucial that a 4th cable could be added to the system as for most median applications this is a pre-requisite. This additional cable also meant slightly more height and strength which allowed TL-4 compliance testing to be completed. Corresponding results satisfied NCHRP 350 TL-4 criteria, also at 3m post spacing.
The TL-3 and TL-4 systems use exactly the same posts so future upgrades from TL-3 to TL-4 is easily achievable.