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Hi,

I was just wondering if you could help clarify a question that came up the other day.

Can you clarify the definition for "start of the first through movement" as opposed to the "start of the second through movement". Would the first be used when there is advance phasing?

Thanks!

Hi, Anne.

The distinction matters when, say, the NB direction of travel has a leading, protected turning phase, and the SB direction does not (that is, the SB direction has only a permitted turning phase or no turning movement at all). In this case, the green for the NB through phase begins earlier in the cycle than the green for SB through phase. If the offset reference point in the controller is the beginning of NBT green, we'd set it in Tru-Traffic to "start of the first through movement", while if the offset instead references the SBT green (which might be the moment in the cycle when simultaneous service to both through movements begins), we'd set it in Tru-Traffic to "start of the second through movement".

Update: Another case where the distinction matters is where the phasing is lead-lead (dual, leading protected turning phases) and the turning phase splits are not equal. As before, one of the through movements will be served before the through in the opposite direction, and the "start of the first through movement" and "start of the second through movement" offset reference points allow us to make the distinction.

Some controllers automatically switch from referencing one through movement to the other as the leading turning movement splits change. These two offset reference options in Tru-Traffic are supposed to mimic this policy.

Regards.
Greg