Traffic Operations and Traffic Signals - IES Previous Year Questions

1. If the normal flows on two approach roads at an intersection are respectively 500 pcu per hr and 300 pcu per hr, the saturation flows are 1600 pcu per hr on each road and the total lost time per signal cycle is 16 s, then the optimum cycle time by Webster’s method is _____ .

[IES 1999, IES 2018]

  1. 58 s
  2. 48 s
  3. 19.3 s
  4. 72.5 s
Answer: Option A
Explanation:
Normal flows, q1 = 500 pcu per hr,   q2 = 300 pcu per hr
Saturation flows, S1 = S2 = 1600 pcu per hr
Total lost time per cycle, L = 16 s
Based on Webster’s method,
Optimum cycle time, C0 =
1.5 L + 5 / 1 - Y

where , Y = y1 + y2 =
q1 / S1
+
q2 / S2
=
500 / 1600
+
300 / 1600
= 0.5
Thus, C0 =
1.5 L + 5 / 1 - Y
=
(1.5 x 16) + 5 / 1 - 0.5

⇒ C0 = 58 s

2. When two roads with two-lane, two-way traffic cross at an uncontrolled intersection, the total number of potential major conflict points would be _____ .

[IES 1999]

  1. 24
  2. 16
  3. 4
  4. 32
Answer: Option B
Explanation:
  • Major conflict points are the points at which crossing of vehicles occur.
  • For a two-lane two-way traffic at an uncontrolled intersection, the total number of major conflict points are 16.

3.  Consider the following factors:

  1. Length of vehicle
  2. Width of vehicle
  3. Approach speed
  4. Stopping time for approaching vehicle
  5. Passing sight distance

Which of these factors are taken into consideration for determining yellow time of a traffic signal at an inner section ?

[IES 2000]

  1. 2, 3 and 4
  2. 1, 3 and 5
  3. 1, 3 and 4
  4. 1, 2 and 5
Answer: Option C
Explanation:
Amber or Yellow time =
S + W + L / v
(or) tr +
v / a

Where,
S - Stopping Sight Distance
W - Width of the intersection
L - Length of the vehicle
tr - Reaction time
v - Approach velocity
a - Retardation
S / v
- Stopping time for approaching vehicle

4.  Which one of the following is the purpose of a divisional island ?

[IES 2001]

  1. To divert the traffic into a definite travel path at the intersection.
  2. To reduce the speed of traffic entering the intersection.
  3. To divert traffic from obstacles and expedite the flow of traffic.
  4. To segregate opposing flow of traffic in a multi-lane highway.
Answer: Option D
Explanation:
The purpose of divisional island is to separate the opposing flow of traffic on a multi-lane highway.

5.  Match List-I (Type of traffic signals) with List-II (Advantages) and select the correct answer using the codes given below the lists:

List-I

  1. Pre-timed signals
  2. Vehicle-Actuated signals
  3. Semi-vehicle actuated signals
  4. Linked traffic signals

List-II

  1. Useful for junction of a side street having low traffic volume with a main street having heavy flow.
  2. Overall optimisation of traffic flow.
  3. Delay is held to a minimum and maximum lane capacity is achieved.
  4. Most successfully used in linked system.

[IES 2003]

Codes: A B C D

  1.  4  3  1  2
  2.  3  4  2  1
  3.  4  3  2  1
  4.  3  4  1  2
Answer: Option D
Explanation:
  • Pre-timed traffic signals are set to repeat regularly a cycle of red, amber and green lights. The timing of each pahse of the cycle is predetermined based on traffic studies, such that the delay is minimum and lane capacity is maximum.
  • In fully actuated traffic signals, the detectors and computers assign the right of way for various traffic movements based on demand and pre-determined programming. Hence, it is useful in linked system.
  • In semi-actuated traffic signals, the normal green phase of an approach may be extended upto a certain period of time for allowing a few vehicles approaching closely, to clear of the intersection with the help of detectors installed at the approaches. Hence, it can be used in a junction of a side street having low traffic volume with a main street having heavy traffic volume.

6.  Assertion (A): Prohibitory signs are part of regulatory signs which give a definite negative instruction regarding movement prohibition, restriction on weight, or speed of vehicles.

Reason (R): According to the IRC standards, prohibitory signs are of octagonal shape with side being 900 mm and with a white border and red background for the standard size.

[IES 2003]

  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not a correct explanation of A.
  3. A is true but R is false.
  4. A is false but R is true.
Answer: Option C
Explanation:
  • Prohibitory signs are a part of regulatory signs.
  • According to IRC standards, regulatory signs are of circular shape of diameter 600 mm and are white in colour with a red border.

7.  The lost time due to starting delay on a traffic signal approach is noted to be 3 seconds, the actual green time is 25 seconds and amber time is 3 seconds. How much is the effective green time ?

[IES 2004]

  1. 25 sec
  2. 27 sec
  3. 31 sec
  4. 19 sec
Answer: Option A
Explanation:
Effective green time, Ge = G + A + L
Where,
G - Actual green time = 25 s
A - Amber time = 3 s
L - Total lost time = Initial lost time + Final lost time = 3 + 0 = 3s
Thus, Ge = 25 + 3 - 3 = 25 s

8.  Which one of the following traffic signal systems is useful when there is continuous operation of a group of vehicles along the main road ?

[IES 2010]

  1. Alternate system
  2. Simple progressive system
  3. Flexible progressive system
  4. Simultaneous system
Answer: Option B
Explanation:
Simple progressive system permits a continuous operation of group of vehicles along the main road by making a time schedule.

9.  Light reflecting devices used to guide the driver along the proper alignment are called _____ .

[IES 2010]

  1. Delineators
  2. Attenuators
  3. Litter bin
  4. Rumble strips
Answer: Option A
Explanation:
Road delineators are devices that are used to outline the roadway to provide virtual assistance to drivers about the alignment of the road ahead, especially at night.

10.  The duration of green time of a traffic signal depends on _____ .

[IES 2015]

  1. Traffic volume
  2. Traffic speed
  3. Traffic density
  4. All the above
Answer: Option A
Explanation:
In general, the duration of green time of a traffic signal depends on the traffic volume during peak hour.
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