Street Design Manual

The storage requirement for a separate turn lane is also based on the amount of queue length necessary to accommodate other vehicles arriving on the approach during the red phase of the cycle.

The “red time” formula for estimating the storage length for other vehicles is as follows: = ∗ ∗ ∗ ( − � ) ( ∗ ) Where, L = storage length of turn lane (feet) V = peak 15 minute flow rate of turning volume (vph) K = constant to reflect random arrivals

K = 2.0 for 95% probability of storing all vehicles K = 1.5 for 90% probability of storing all vehicles 25 = approximate length of vehicle (feet per vehicle)

G = green time (seconds) C = cycle length (seconds) N = number of cycles for hour l = number of approaching vehicle lanes

B. Unsignalized Intersection The storage length for turning vehicles at intersections not controlled by a traffic signal should be determined by using the formulas for signalized intersections as outlined above. Storage requirements should be based on an assumed minimum cycle length of 90 seconds. C. Right Turn/Deceleration Lengths The lengths required to come to a stop from either the design speed or an average running speed of a roadway, are indicated in the following table. The lengths assume the roadway is on a two percent or less vertical grade. The desirable deceleration lengths should be used on new roadways and the minimum may be used along existing roadways. Longer deceleration lengths may be required on downgrades greater than two percent.

Raleigh Street Design Manual – Page 93