Yes North American controllers are incredibly cumbersome and archaic. You cannot comprehend how frustrating it is to deal with this kind of nonsense after having worked on traffic signals in the Netherlands that actually work in a logical way.
An overlap is a signal group that is not actually included in the phase structure, it sort of exists separately and you need to define its state relative to other phases that are actually in the phase structure. It is an absurd solution to the self-inflicted constraints created by the "ring and barrier" phase structure. which usually only includes 8 phases at a standard intersection.
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For example if you wanted to add a northbound right turn phase, you'd create an "overlap" of phase 7, telling the right turn signal to turn green whenever the westbound left turn phase does. Or if you're really fancy you'd tell it to overlap with both phase 6 and phase 7, but only if the pedestrian phase for phase 6 isn't on (because the ped phase conflicts with the right turn).
The ring and barrier structure is how they used to control signals when there was a literal ring with metal strips on it that would rotate and complete different circuits as different parts passed by the electrical contactor. So different lights get connected to power at different points in the ring's cycle. The barriers connected rings together at certain points in the cycle to prevent them from getting out of sync with each other.
In the Netherlands in the 1990's they realized that computers exist so there's no need for this arbitrary organization of signal groups. You can just tell the computer which movements can go at the same time as each other using a conflict matrix. (Which is something North American controllers also have!) A computer is perfectly capable of figuring out which signal groups are valid to combine based on the constrants the engineer has specified.
To this day North American controller manufacturers still use the ring-barrier structure, now offering four-ring controllers! Which still doesn't solve the probem because there is no way to arrange right turn phases in a ring-barrier structure that allows them to turn green at all of the moments when they should logically be able to!
In the Netherlands there's no such thing as an overlap. Every signal group is controlled directly and is included separately in the conflict matrix. If you want a predefined relationship between specific signal groups you can program that, but it's not baked into the control structure. So the Dutch standard numbering scheme includes a separate number for each movement. 1-12 are the usual vehicle movements, 21-28 are the usual bike movements (each leg accommodates 2-stage crossing with a green wave between them), 31-38 are the typical ped movements (again two-stage crossings), 41-52 are the 12 vehicle movements for transit signals, 61-72 are the 12 movements for vehicles if there's a second stage within the intersection (or a pre-signal), 81-88 are the usual bike movements in the contraflow direction (e.g. for two-way paths), again assuming two-stage crossings, and 91-98 are in case you need to use different signal groups for different directions on the same crosswalk (e.g. to enforce a pedestrian green wave). Here's a hypothetical intersection with its signal phases numbered. You'll note that every movement has a different number because they're controlled separately.
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Image from wegenwiki
Meanwhile in simple old America, here's the standard numbering for signal phases at intersections. They give you 8 numbers. The pedestrian phase is the same phase as the adjacent vehicle phase.
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You can always make up numbers for whatever you want, but the fact that the standard doesn't even consider the possibility of a right turn signal says a lot.
The pedestrian signal and the parallel vehicle signal are separate signal groups in the Netherlands because combining them into the same signal group would be stupid. A right turn phase along a street conflicts with the pedestrian phase to its right but not the vehicle phase to its left so of course those need to be controlled differently to each other.
Meanwhile the ring-barrier structure prevents valid combinations such as Phase 6 Pedestrian with Phase 3 Vehicle, because the signal thinks those two phases conflict. But in fact it's only the vehicle portion of phase 6 that conflicts with phase 3, not the pedestrians. And lord help you if you want to control the right turn signal based on the actual amount of traffic in the right turn lane, instead of just copying the signal states from a different movement.
