EXAM 2

Question 1

(TRUE or FALSE) A 3 phase traffic signal must have a longer cycle length than a 2 - phase one.

Answer 1

False

Question 2

Difference between a “protected movement” and a “permitted movement”

Answer 2

A protected movement has the right of way to proceed through an intersection. A permitted movement must yield to others first

Question 3

What is the “saturation flow” of an approach?

Answer 3

It is the maximum flow possible through an intersection for a movement from an approach if that approach has all of the green time.

Question 4

(TRUE or FALSE)

A left turn lane cannot be included in the same lane group as a through lane.

Answer 4

True

Question 5

In traffic flow, what is the differenc between ‘headway’ and ‘gap’?

Answer 5

Headways is the separation in the time or space between 2 consecutive vehicles using the same reference point (e.g., front to front, rear to rear). Gap is the separation in time or space from the rear of one vehicle to the front of the nexxt vehicle

Question 6

What is the foundational assumption of the Greenshields Model?

Answer 6

The speed - density relationship is linear

Question 7

In calculating traffic signal timing “Lost Time” accounts for two things. What are they?

Answer 7

Start up of vehicles & clearance of intersection

Question 8

In general, does increasing the number of phases in a traffic signal plan increase, decrease, or have no effect on the traffic flow efficiency of an intersection?

Answer 8

Decrease

Question 9

What is the “headway” and what are its approrpiate units?

Answer 9

Headway is the separation in time between two or more consecutive vehicles measured from simular location (e.g. front bumpers) of the vehicle units = time (seconds) per vehicle

Question 10

When conducting counts of motor vehicle traffic, why is it important to count passenger cars, trucks, and buses separately?

Answer 10

Passenger cars, trucks & buses are different in size & they may behave differently ( e.g. different speeds, acceleration / decceleration)

Question 11

How many critical lane groups are there for each phase of a traffic signal plan?

Answer 11

1

Question 12

When considereing a set o flane groups, the critical lane group always has the highest value of what?

Answer 12

Volume/ saturation flow rate (V/S)

Question 13

What does “Peak Hour Factor (PHF)” represent?

Answer 13

PHF represents the distribution of traffic flow over an hour. It is 1 when there’s no fluctuations & 0.25 if theres extreme peaking

Question 14

Is “Time Mean Speed” Calculated using data measured at a point or section?

Answer 14

Point

Question 15

Can “Time Mean Speed” be greater than “Space Mean Speed” Why?

Answer 15

Yes

Question 16

The Pousson Model of vehicle arrivals has two important assumptions. What are they?

Answer 16

1) arrival of each vehicle is independent
2) Flow rate over a short perod of time is constant