Drivers prefer right turns to cross to a service road on the intersection approach

Submitted by john on Sun, 15/12/2019 - 18:43
crossover

(in US: Drivers prefer left turns to cross to a service road on the intersection approach.)

For two-phase benefits, right turns can either:
(a) cross-over, by crossing the opposing through flow on the approach;
(b) P-turn, by going through, U-turn, then left turn;
(c) Q-turn, by going` left turn, then U-turn;
(d) parallel flow, by turning right from the conventional location, but into a near-side service road; or
(e) use a diverging diamond interchange.
 

(a) Crossover
A crossover is the preferred option because the right turner enters the turn lane at the same location as usual; turners pass through the intersection only once; the turn alignment looks, and is, a short cut with a better than normal alignment. This is particularly advantageous for trucks and at intersections with acute angles where split phases are currently necessary, because opposing turns cannot turn at once as a result of the geometry, so through and right from one direction proceed together.

Note that the right turn lane(s) cross to a right hand service road half way towards the intersection, usually under signal control; and the alignment of the opposing through movement forms a plait with the right turn lane, staying within the current intersection footprint.
The opposing through flow has high alignment standards. The right turn has sharper curves yet low off-tracking if the turn radii are at least 30m. The right turners potentially queue twice but since the cycle time is shorter, the total storage length is about the same, so intersection flaring does not need to be lengthened.
The simulation of Victoria St, Hoddle St shows crossovers on the north and west approaches. A crossover only interrupts one carriageway, so signals can be perfectly timed to link with the main intersection, and not disrupt the through movements. The right turners then cross in the shadow of the cross street operation. As shown in the simulation, signal timing often means that turners are not stopped at the second stop line (it is continuous flow by chance).

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