1. Norman W. Garrick Example of a Shock Wave At a Stop Traffic is flowing normal Flow, q = 500 veh/hr Conc, k = 10 veh/mi T = t 1 sec

2. Norman W. Garrick Example of a Shock Wave At a Stop T = t 2 sec Flagman stops first vehicle in the queue Shockwave

3. Norman W. Garrick Example of a Shock Wave At a Stop T = t 3 sec More vehicles have joined the queue The shockwave have moved backwards Shockwave 1 On either side of the shockwave there are two different state of flow State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi

4. Norman W. Garrick Example of a Shock Wave At a Stop T = t 4 sec Flagman releases queue Shockwave 1 There is now a second shockwave and a third state of flow - the flow state for traffic released from the queue Shockwave 2 State 3 q = 1000 veh/hr k = 110 veh/mi State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi

5. Norman W. Garrick Distance-Time Diagram for Shock Wave Distance Time X Shockwave 1 Shockwave 2

6. Norman W. Garrick Calculation of Shockwave Travel The speed of the shockwave can be calculated using the above equation The sign is important so remember to number the travel states from upstream to downstream If the sign is +ve it means that the shockwave is moving downstream u sw = (q 2 -q 1 ) / (k 2 -k 1 ) Shockwave 1 State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi

7. Norman W. Garrick Calculation of Shockwave Travel Shockwave 1 State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi u sw1 = (q 2 -q 1 ) / (k 2 -k 1 ) (0-500) / (260-10) = - 2 mph Shockwave 1 is moving downstream at 2 mph What is the length of the queue after 3 minutes Length = u*t = 2 mph * 3/60 hr = 0.1 mile How many vehicles are in the queue after 3 minutes no. of vehicles = k * L = 250 *0.1 = 25 vehicles

8. Norman W. Garrick Calculation of Shockwave Travel u sw2 = (q 3 -q 2 ) / (k 3 -k 2 ) (1000-0) / (110-260) = - 6.67 mph Shockwave 2 is moving downstream at 6.67 mph Shockwave 1 Shockwave 2 State 3 q = 1000 veh/hr k = 110 veh/mi State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi

9. Norman W. Garrick Calculation of Shockwave Travel How long will it take to clear the queue if the flagman held the queue for 3 minutes Length after 3 minutes = u*t = 2 mph * 3/60 hr = 0.1 mile u sw1 = - 2 mphu sw2 = - 6.67 mph Therefore the queue will dissipate at rate of 4.67 mph Time to dissipate a 0.1 mile queue is L/speed 0.1 mile / 4.67 mph = 0.021 hr = 12.6 minutes Shockwave 1 Shockwave 2 State 3 q = 1000 veh/hr k = 110 veh/mi State 1 q = 500 veh/hr k = 10 veh/mi State 2 q = 0 veh/hr k = 260 veh/mi

10. Norman W. Garrick

12. 8 vehicles 7 space Get Distance to find average spacing

13. Norman W. Garrick 37.7 32.0