Explain the Clearance Interval - Signalized Intersections 

Also known as "Red Clearance Interval" and "All Red"       

r = (w+L) / V - If there is no pedestrian traffic

r = (P+L) / V If there is pedestrian traffic or the crosswalk is protected by ped. Signal

Where:  r = length of red clearance interval (sec)

w = width of intersection; more precisely, the length of the vehicle path from the departure stop line to the far side of farthest conflicting traffic lane (ft)

P = width of intersection; more precisely, the length of the vehicle path from the departure stop line to the far side of farthest conflicting ped crosswalk (ft)

L = Length of vehicle (20 ft generally used)

v = speed of vehicle through intersection (fps)