The Rule of turning bridges is a principle of block pushing similar to the rule of double bridges, but used whenever the bridge begins to turn, hence its name. As a bridge one square wide cannot be turned, unless Chip has flippers and needs to use the blocks for some other purpose than filling in water, a double bridge has to be built out into the water, and then using the space on the side, Chip can then turn.
Generally, the rules of double bridges and turning bridges can be combined, even for extremely trivial gains.
After using the rule of double bridges on the top two water spaces, fill space [5, 5], then stick a second block onto space [5, 5], which allows spaces [6, 5] and [4, 5] to be filled in succession.
Generally, the rule of turning bridges produces equal gains to using the rule of double bridges on the final two blocks, and then building as normal. However, there are situations where the rule of turning bridges is preferable: when, for some reason, building one block on the nearer bridge, then one on the further bridge, and then as normal is slower than building one on the nearer bridge, stuffing one block into this same space, and then building one on the further bridge and then immediately continuing. These can include monster interference, severe congestion in the block area which requires several blocks to be moved out before others can be moved, and also if the items being removed are bombs rather than water.
In the latter case, there is no difference what is used up until the point when turns are made. When bombs are being removed, there is no dirt to pick up, which causes the rule of turning bridges to be preferable at any time.
Each application of the rule of turning bridges saves 2 moves, but usually the rule of double bridges will work just as well. Use the rule of turning bridges even more judiciously; there are very specific situations where each rule is usable.
While the two rules are similar, the rule of turning bridges is less used than the rule of double bridges. Levels where this can be used include Mind Block, Cityblock, and the corners of Writers Block.