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ODOT does not currently specify a minimum length of median cable rail for a singular run, but the question came up on what should be the minimum. I was looking into design guidance from other DOTs and noticed it varies quite a bit:

• NYSDOT has a minimum length of 500’ between outer ends of terminals.


• Colorado DOT requires a .2-mile uninterrupted length per installation.


• Wisconsin DOT recommends a minimum length of 300’ excluding the end anchorages.


• Texas DOT says to see manufacturers guidance for allowable minimum length runs.

I am hesitant to put in our design guidance to “see manufacturers guidance” because we have 5 approved systems and the designer cannot predict which system will be chosen by the contractor. With there being different proprietary systems, it could vary, but I am just looking for a reasonable minimum length that will ensure proper tensioning in the system is maintained and deflections will not greatly exceed what we anticipate. Between your experience with proprietary cable systems and the development of the Midwest cable system, what would be your recommendation for a minimum install length?

Thank you,

In terms of minimum system lengths for cable barriers, we cannot provide direct numbers for any given system that we did not design. However, we can discuss potential guidance for consideration.

Existing cable barrier testing has been conducted on relatively short lengths of 300’ or less, prior to minimum system length updates that were introduced in MASH 2016. Shorter system lengths tend to increase overall anchor loads to some degree, but also decrease deflection as tension is developed in the cables more quickly due to the shorter length and the amount of cable stretch under load is reduced with shorter cables. MASH was updated in 2016 to provide a minimum system length of 600’ for cable barrier testing to create a consistent system length for testing and comparison of systems.

It is likely that cable systems can be used safely under shorter system lengths up to a point. A reasonable metric may be to take guidance provided in MASH for minimum length for crash testing of longitudinal barriers. MASH recommends testing a minimum system length of three times the deflected length of the system. This is recommended to ensure that the system performance is not significantly affected by proximity of the impact to the end anchorages. Based on this guidance, if a given cable barrier system deflected for 100’ along its length in test no. 3-11, a reasonable minimum system length would be 300’ including the anchorages.

For now, that might be the best guidance we can provide. It is likely conservative, but testing would be required to fully investigate the minimum system length of most barriers. Note that one would still need to consider any guidance regarding the length required for end anchorages as well as length required to shield a given hazard. Additionally, manufacturer guidance that suggests longer lengths should be followed if available.

Tensioning should be more consistent with shorter systems as the effect of thermal variation in cable length will be reduced for shorter cable lengths.

Thanks!