Lecture 4 - Traffic Flow Fundamentals

Question 1

is the phenomenon of backups and queuing on a highway due to a sudden reduction of the capacity of the highway.

Answer 1

Bottleneck condition

Question 2

When such a condition exists, and the normal flow and density on the highway are relatively large, the speeds of the vehicles will have to be _____ while passing the bottleneck.

Answer 2

reduced

Question 3

The point at which the speed reduction takes place can be approximately noted by the turning on of the ______ of the vehicles.

Answer 3

brake lights

Question 4

An observer will see that this point moves upstream as traffic continues to approach the vicinity of the bottleneck indicating an upstream movement of the point at which flow and density change.

Answer 4

shock wave

Question 5

also exists when the capacity suddenly increases, but in this case, the speeds of the vehicles tend to increase as the vehicles pass the section of the road where the capacity increases.

Answer 5

shock wave

Question 6

Several types of shock waves can be formed, depending on the traffic conditions that lead to their formation

Answer 6

1. Frontal stationary shock waves
2. Backward forming shock waves
3. Backward recovery shock waves
4. Rear stationary and forward recovery shock waves

Question 7

________ are formed when the capacity suddenly reduces to zero at an approach, or set of lanes having the red indication at a signalized intersection, or when a highway is completely closed because of a serious incident.

Answer 7

Frontal stationary shock wave

Question 8

__________ are formed when the capacity is reduced below the demand flow rate resulting in the formation of a queue upstream of the bottleneck. This may occur at the approach of a signalized intersection when the signal indication is turning red, or at a location of a highway where the number of lanes is reduced.

Answer 8

Backward forming shock waves

Question 9

_________ are formed when the demand flow rate becomes less than the capacity of the bottleneck or the restriction causing the capacity reduction at the bottleneck is removed.

Answer 9

Backward recovery shock waves

Question 10

For example, when the signals at an approach or set of lanes on a signalized intersection changed from red to green, the flow restriction is removed; the traffic on that approach or set of lanes is free to move across the intersection.

Answer 10

Backward recovery shock waves

Question 11

_________ are formed when demand flow rate upstream of a bottleneck is first higher than the capacity of the bottleneck and the demand flow rate reduces to the capacity of the bottleneck

Answer 11

Rear stationary and forward recovery shock waves

Question 12

For example, during the off-peak period when the demand capacity is less than the tunnel capacity, no shock wave is formed. When the demand capacity becomes higher than the tunnel capacity during the peak hour, a backward forming shock wave is formed.

Answer 12

Rear stationary and forward recovery shock waves

Question 13

As the end of the peak period approaches, the demand flow rate tends to decrease until the same as the tunnel capacity, called the ________

Answer 13

rear stationary shock wave.

Question 14

before complete closure

Answer 14

Frontal stationary shock waves

Question 15

when signals turn from green to red

Answer 15

Backward forming shock waves

Question 16

when signals turn from red to green

Answer 16

Backward recovery shock waves