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Calcimator

Turn Lane Length Calculator

Calculate deceleration, storage, and taper lengths for left and right turn lanes based on AASHTO design standards.

Inputs

mph
veh/hr
sec
%

Results

Total Length (with taper)

412 ft

≈ 10 school buses

Decel + Storage280 ft
Deceleration Length218 ft
Storage Length62 ft
Taper Length132 ft
Design Queue3 vehicles
Lane Width11 ft
How to Use This Calculator
  1. Enter Turn Lane Type, Left Turn, and Right Turn.
  2. Set Approach Speed, Turning Volume, and Signal Cycle Length.
  3. Adjust Green Ratio (g/C), Approach Grade as needed.
  4. Review the Total Length (with taper) (ft) result.
  5. Use Decel + Storage (ft) and Deceleration Length (ft) to inform your decision.

How the result changes with Approach Speed

Approach SpeedTotal Length (with taper)
25217 ft
36311 ft
49452 ft
61627 ft

What each input means

Turn Lane Type
Type of turn lane being designed.
Approach Speed
Design speed or 85th percentile approach speed.
Turning Volume
Peak-hour volume of turning vehicles.
Signal Cycle Length
Signal cycle length in seconds. Enter 0 for unsignalized intersections.
Green Ratio (g/C)
Ratio of effective green time to cycle length for the turning phase.
Approach Grade
Grade on approach. Negative = downhill (longer deceleration needed).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Turn Lane Type = 1, Approach Speed = 45, Turning Volume = 100, Signal Cycle Length = 90 = 6 input(s) provided
  2. Calculate Total Length
    Total Length
    412 = 412
  3. Calculate Decel + Storage
    Decel + Storage
    280 = 280
  4. Calculate Deceleration Length
    Deceleration Length
    218 = 218

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