Collisions

The question of when it is appropriate to have people "collide and take right hands" (sometimes called the "same position rule") is a controversial one. Opinions vary, from those who don't believe collisions should ever be used, to those who believe Lockit is legal from inverted lines. Most people accept the historically common usage in various types of "ends move up" actions in Chain Reaction, Motivate, Tally Ho, etc., and the very similar action of coming to the same point or end spot on Diamond Circulate, Flip or Cut the Diamond, or 6x2 Acey Deucey.

A thing to be very clear about is that "collide and take right hands" applies only when a call finishes with two people sent to the same spot as a result of the complete execution. There is a similar-appearing situation when a call is stopped prematurely, because of an interruption or fractionalization. When this happens, the definition of the call must have had them passing right or left shoulders. In such a case, they stop during the pass, forming a miniwave of corresponding handedness.

\phfour{b2n,g2n,g3s,b3s}	\pvBBBB{.+.,b3w,.+.,g3e,g2w,.+.,b2e,.+.}

before 3/4 Run Wild	finished; people doing the Cross Run take the outside track

This sometimes requires paying careful attention to the paths that people take. When the paths coincide exactly, the right shoulder rule applies, and people take right hands if they stop at that point. If the paths do not coincide exactly, they follow the appropriate traffic rule.

\syhlines{b3w,g4n,b4w,g1n}	\svthreebyonedmd{g1w,g4e,b4w,b1n}

before 1/2 Circulate	finished; there were no actual collisions

In all cases the people who come to the same spot must be facing opposite directions. The rule is that they take right hands even if the call had the word "Left" in it, as in Left Chain Reaction. (Left Chain Reaction calls for a left Hinge.) However, if the "Mirror" concept is in force, everything is Mirror, including collisions.

When collisions occur at the end of a call, people's resultant positions aren't the usual ones, and it becomes necessary to figure out where the "extra" people go. The general rule is that they slide "outwards". People not involved in collisions are not supposed to move from their natural positions unless absolutely necessary. In the simple case of a collision on a "move up", the result is therefore typically a parallelogram.

\syhDBDs{b4e,b1e,g1w,g2e}	\syvBBBs{b2e,.+.,g2w,.+.,b1w,g3e}

before Chain Reaction, Turn the Star 1/2	after

\sxhlines{b2s,g1n,g2s,b1s}	\syvBBBs{.+.,b4e,.+.,b3w,g1w,g4w}

before Lockit	after

Sometimes the people not involved in the collision have to move, but this is really just "breathing".

\syhlines{g3s,b3n,g2s,b2s}	\syvlines{b3e,g2w,g3e,b2w}

before unesthetic Lockit	after

Sometimes people might be tempted to "leave space for the phantoms", or "maintain symmetry" but this is often wrong.

\sxvlines{g3e,b3e,g2w,b2e}	\sxhLLLs{g3s,b2n,b3s,g2n,.+.,.+.}

before Lockit	after doing it wrong; there are no phantoms going into the center spots; result should be a 1x8

For some calls, collisions occur in multiple places. Everyone moves outward from the center of the overall formation.

\syhlines{g3n,b3n,g2s,b2s}	\sxhBBBBs{b2s,.+.,b1n,.+.,g2s,.+.,g1n,.+.}

before Split Circulate	after

\syhlines{g3n,b3s,g2n,b2s}	\sxhBBBBs{b2s,.+.,g4n,.+.,b3s,.+.,g1n,.+.}

before Scatter Circulate	after

Here is a rather peculiar situation that seems to be accepted in common practice.

\syhlines{g3n,b3n,g2s,b2s}	\sxhBBBBs{b2s,.+.,b1n,.+.,.+.,g3s,.+.,g4n}

before Go First Class	after

The boys moved out farther than necessary, presumably to make the resultant setup nicer.

The subject of collisions is not completely logical, consistent, or free of controversy.

In addition to controversy over what collisions are appropriate, there is controversy over whether one should "re-evaluate" and continue from the new formation after a collision arising in part of a compound call. There are those who consider Split Motivate legal from a starting DPT, and those who do not.