Channelized intersections: advantages and disadvantages

A channelised intersection is an at-grade junction in which traffic movements are guided into definite paths by raised or painted islands, kerbs and markings, so that conflicts are separated and the paved area is reduced (IRC:SP:41).

        |  |  |
        |  |  |  <- splitter island
   _____|  |  |_____
  /     \  \  /     \
 ---  triangular      ---
  \_____/ island \_____/
        |  |  |

How it works

• Islands (triangular, divisional, refuge) force vehicles into turning or through lanes.
• Turning roadways with large radius give free left turns (for left-hand traffic), so those vehicles do not wait for the signal.
• Markings, signs and signals work together with the islands.

Advantages

• Reduces the number and severity of conflicts, so crashes fall.
• Separates movements and fixes the vehicle path, so there is less confusion and wrong-way driving.
• Reduces the large paved area, which limits vehicle wandering and speed.
• Provides refuge for pedestrians and a place for signs, signals and lighting.
• Increases capacity (free turns, separate turn lanes) and reduces delay.
• Gives control of speed and angle of merging; allows protected turning lanes.

Disadvantages

• Higher cost of construction and kerbs, and more land for turning roadways.
• Islands are hazards if poorly marked or lit, especially at night; vehicles may hit them.
• Hard for large vehicles to turn if radii or lane widths are too small.
• Too much channelisation can confuse drivers and block snow or debris clearing, and complicates future widening.
• Long walking distance for pedestrians if they must cross many lanes.