3-transportation Engineering-i Updated.pdf

Transportation -I Lecture 3

By Engr. Muhammad Waseem Lecturer Department of Civil Engineering UET, Jalozai 1

Traffic Signals ➢ A traffic signal is advice which is normally electrically or mechanically operated so that traffic alternatively directed to stop and permitted. ➢ It consist of: ➢ A signal head and control mechanism ➢ Control mechanism may be: 1. Local control mechanism 2. Central control mechanism 2

Traffic Signals Types (MUTCD) ➢ Traffic control signals (most common) ➢ Pedestrian signals (WALK, DON’T WALK, UPRAISED HAND) ➢ Emergency vehicle traffic control signals ➢ Traffic control signals for one-lane, two-way facilities ➢ Traffic control signals for freeway entrance ramps ➢ Traffic control signals for moveable bridges ➢ Lane-use control signals (reversible lanes on bridges or tunnels or streets/highways) ➢ Flashing beacons (Hazard or critical control device) 3

Advantages of Traffic Signals ➢ Orderly movement of traffic ➢ Reduces certain types of crashes

➢ Interrupts heavy flows for minor movements ➢ Promotes driver confidence

➢ Provides gap for minor movements ➢ Capacity of intersection movement is increased

4

Advantages of Traffic Signals ➢ Traffic signals, when properly installed and operated at appropriate locations, provide a number of significant benefits ❑ With appropriate physical designs, control measures, and signal timing, the capacity of critical intersection movements is increased. ❑ The frequency and severity of accidents is reduced for certain types of crashes, including right-angle, turn, and pedestrian accidents.

5

Advantages of Traffic Signals ❑ When properly coordinated, signals can provide for nearly continuous movement of through traffic along an arterial at a designated speed under favorable traffic conditions. ❑ They provide for interruptions in heavy traffic streams to permit crossing vehicular and pedestrian traffic to safely cross.

6

Disadvantages of Traffic Signals ➢ At the same time, misapplied or poorly designed signals can cause: ➢ Excessive delay ➢ Signal violations ➢ Increased accidents (particularly rear-end accidents) ➢ Drivers rerouting their trips to less appropriate routes

7

Signal Indications ➢ Green ball. ➢ A steady green circular indication allows vehicular traffic facing the ball to enter the intersection to travel straight through the intersection or

to turn right or left. ➢ Yellow ball. ➢ The steady yellow circular indication is a transition between the Green Ball and the Red Ball indication. ➢ It warns drivers that the related green movement is being terminated or that a red indication will immediately follow. In general, drivers are permitted to enter the intersection on “yellow,” but are prohibited from doing so on the “red” that follows it. 8

Signal Indications ➢ Red ball ➢ The steady red circular indication requires all traffic (vehicular and pedestrian) facing it to stop at the STOP line ➢ Flashing ball ➢ A flashing “yellow” allows traffic to proceed with caution through the intersection. ➢ A flashing “red” has the same meaning as a STOP sign-the driver may proceed with caution after coming to a complete stop.

9

Signal Operation ➢ Continuous operation of traffic control signals is critical for safety. ➢ No signal face should ever be “dark” (i.e. with no lens illuminated). ➢ In cases where signalization is not deemed necessary at night, signals must be operated in the flashing mode (“yellow” for one street and “red” for the other). ➢ Signal operations must also be designed to allow flashing operation to be maintained even when the signal controller is undergoing maintenance or replacement. 10

Traffic Signal Controllers ➢ Individual traffic controllers may operate in the pretimed or actuated mode. ➢ In pretimed operation, the sequence and timing of every signal indication is preset and is repeated in each signal cycle. ➢ In actuated operation, the sequence and timing of some or all of the green indications may change on a cycle-by-cycle basis in response to detected vehicular and pedestrian demand.

11

Traffic Signal Controllers ➢ Pretimed Operation: ➢ In pretimed operation, the cycle length, phase sequence, and timing of each interval are constant. ➢ Each cycle of the signal follows the same predetermined plan.

12

Traffic Signal Controllers ➢ Semi-Actuated Operation: ➢ In semi-actuated operation, detectors are placed on the minor approach(es) to the intersection; No detectors on the major street. ➢ Used at intersections where one of the streets carries low traffic volume ➢ The light is green for the major street at all times except when

a “call” or actuation is noted on one of the minor approaches.

13

Traffic Signal Controllers ➢ Fully-Actuated Operation: ➢ In fully actuated operation, every lane of every approach must be monitored by a detector. ➢ Fully-actuated signals are used at intersections where both the streets are busy.

➢ Green time is allocated in accordance with information from detectors and programmed “rules” established in the controller for capturing and retaining the green. ➢ In full actuated operation, the cycle length, sequence of phases, and green time split may vary from cycle to cycle. 14

Traffic Signal Design Terminology ➢ Phase ➢ Cycle

➢ Cycle Time

15

Two Phases Signal ➢ Adopted if through traffic is significant compared to the turning movements. Intersection is operated with two green intervals

16

Four Phases Signal ➢ Flow from each approach is put into a single phase avoiding all conflicts. ➢ Ideally suited in urban areas where the turning movements are comparable with through movements and when through traffic and turning traffic need to share same lane

17

Traffic Signal Design Terminology ➢ Cycle ➢ A signal cycle is one complete rotation through all of the indications provided. ➢ Every legal vehicular movement receives a “green” indication during each cycle, although there are some exceptions to this rule ➢ Cycle Length (C)

Green, G Yellow Red

Cycle, C

➢ Total time to complete one full cycle of indications. Indicated by “C” 18

Traffic Signal Design Terminology ❑ Interval ❑ The interval is a period of time during which no signal indication changes.

❑ There are several types of intervals within a signal cycle:

➢ Green Interval/Time (Gi) ➢ The duration of the green indication of a given movement at a signalized intersection

➢ Red Interval/Time (Ri) ➢ The period in the signal cycle during which, for a given phase or lane group, the signal is red 19

Traffic Signal Design Terminology ➢ Change Interval (y) ➢ Yellow time ➢ Part of transition from “green” to “red” ➢ The period in the signal cycle during which, for a given phase or lane group, the signal is yellow ➢ movements about to lose “green” are given a “yellow” signal, while all other movements have a “red” signal. ➢ It is timed to allow a vehicle that cannot safely stop when the “green” is withdrawn to enter the intersection legally.

➢ Clearance Interval (ar) ➢ All red time ➢ Part of transition from “green” to “red” ➢ The period in the signal cycle during which all approaches have a red indication ➢ During the clearance interval, all movements have a “red” signal. ➢ It is timed to allow a vehicle that legally enters the intersection on “yellow” to safely cross the intersection before conflicting flows are released. 20

Traffic Signal Design Terminology ➢ Phase ➢ A signal phase consists of a green interval, plus the change and clearance intervals that follow it. It is set of intervals that allows designated movement or set of movements to flow and safely halted before release of a conflicting set of movements. Phase 1

Phase 2

EW Street NS Street

21

Traffic Signal Design Terminology ➢ Start-up Lost Time (l1) ➢ Time used by the first few vehicles in a queue while reacting to the

initiation

of

the

green

phase

and

accelerating.

2 seconds is typical. ➢ Clearance Lost Time (l2) ➢ Clearance lost time is defined as the time interval between the last vehicle’s front wheels crossing the stop line, and the initiation of the GREEN for the next phase 22

Traffic Signal Design Terminology ➢ Total Lost Time (tLi) ➢ If the start-up lost time occurs each time a queue starts to move and the clearance lost time occurs each time the flow of vehicles stops, then for each GREEN phase: ➢Time when an intersection is not effectively used by any approach ➢total lost time per phase, s/phase = tLi = l1 + l2

23

Traffic Signal Design Terminology ➢ Effective Green Time (g) ➢ Time actually available for movement ➢ For any given set of movements, effective green time is the amount of time

that vehicles are moving (at a rate of one vehicle every h seconds). ➢ 𝑔𝑖 = 𝐺𝑖 + 𝑌𝑖 − 𝑡𝐿𝑖 Where g i = Effective green time for movment(s) i, (Seconds) Gi = Actual green time for movment(s) i, (Seconds) Yi = Sum of yellow and all red intervals for movment(s) i, (Seconds) t Li = Total lost time for movment(s) i, (Seconds)

24

Traffic Signal Design Terminology Flow rate Saturation Flow Rate

Start-up lost time t1

Extension of green time

Time

Effective Green

Effective Red

Traffic Signal Design Terminology ➢ Critical Lane ➢ The “critical-lane” concept involves the identification of specific lane movements that will control the timing of a given signal phase.

➢ During any green signal phase, several lanes on one or more approaches are permitted to move. ➢ One of these will have the most intense traffic. Thus it requires more time than any other lane moving at the same time. ➢ If sufficient time is allocated for this lane, then all other lanes will also be well accommodated. ➢ There will be one and only one critical lane in each signal phase. ➢ The volume of this critical lane is called critical lane volume 26

Signal Timings and Design Two Phase Signal

27

Key Steps In Signal Timings And Design 1. Development of a safe and effective phase plan and sequence 2. Determination of vehicular signal needs: a. Timing of “yellow” (change) and “all-red’’ (clearance) intervals for each signal phase b.Determination of the sum of critical lane volumes c. Determination of lost times per phase and per cycle d.Determination of an appropriate cycle length

e. Allocation of effective green time to the various phases defined in the phase plan often referred to as “splitting” the green 28

Signal Timing and Design Example ➢ Consider the intersection of two streets with one lane in each direction and relatively low

turning volumes. Considering the following conditions Design the signalized intersection having moderate pedestrian activity ➢ PHF = 0.92

➢ Target V/c = 0.90 ➢ All lanes = 15 ft ➢ Avg. Speed = 30 mph ➢ Level grades ➢ Crosswalks = 10 ft ➢ Driver reaction time = 1.0 s ➢ Deceleration rate = 10 ft/s-sqr

29

Signal Timing and Design Example

N 10 5 400 8

12 420

315

12 10 375 6

10

30

Signal Timing and Design Example

N

454

470

397 433

Phase Plan Considered: 2 Phase Signal 31

Signal Timing and Design Example ➢ Determine Yellow Interval

1.47S 85 y=t+ 2a + (64.4  0.01G ) ➢ y = length of the yellow interval, sec ➢ t = driver reaction time, sec ➢ S(85) = 85th percentile speed of approaching vehicles, or speed limit, as appropriate, mi/h ➢ a = deceleration rate of vehicles, ft/s2 ➢ G= grade of approach, % 32

Signal Timing and Design Example ➢ Determine Yellow Interval

S 85 = 30 + 5 = 35mph S15 = 30 − 5 = 25mph

The average approach speed for all approaches is 30 mi/h. Thus, the S85, = 30 + 5 = 35 mi/h, and the S15 = 30 - 5 = 25 mi/h

1.47S 85 y=t+ 2a + (64.4  0.01G ) 1.47  35 y = 1.0 + = 3.6 s 2(10) + (64.4  0.01 0) 33

Signal Timing and Design Example ➢ Length of all-red clearance intervals ➢ No pedestrian traffic

➢ Significant pedestrian traffic

➢ Some pedestrian traffic

34

Signal Timing and Design Example ➢ ar = length of the all-red phase, sec ➢ w = distance from the departure STOP line to the far side of the farthest conflicting traffic lane, ft ➢ P = distance from the departure STOP line to the far side of the farthest conflicting crosswalk, ft ➢ L = length of a standard vehicle, usually taken to be 18-20 ft ➢ S (I5) = 15th percentile speed of approaching traffic, or speed limit, as appropriate, mi/h

35

Signal Timing and Design Example Length of all-red clearance intervals 𝑺𝟖𝟓 = 𝟑𝟎 + 𝟓 = 𝟑𝟓𝒎𝒑𝒉 𝑺𝟏𝟓 = 𝟑𝟎 − 𝟓 = 𝟐𝟓𝒎𝒑𝒉 𝒘+𝑳 𝟑𝟎 + 𝟐𝟎 𝒂𝒓 = = = 𝟏. 𝟑𝟔 𝒔𝒆𝒄 𝟏. 𝟒𝟕𝑺𝟏𝟓 𝟏. 𝟒𝟕 × 𝟐𝟓

✓.

𝑷 𝟒𝟎 𝒂𝒓 = = = 𝟏. 𝟎𝟗 𝟏. 𝟒𝟕𝑺𝟏𝟓 𝟏. 𝟒𝟕 × 𝟐𝟓

36

Signal Timing and Phasing ➢ Determine Critical Lane Volumes Ring 1 470

Ring 2 397

470 or 397 VcA = 470tvu / h

A

B

454

433

454 or 433 VcB = 454tvu / h

Vc = 470 + 454 = 924tvu / h 37

Signal Timing and Design Example ➢ Determination of Lost Time:

Y = y + ar = 3.6 + 1.36 = 4.96s l 2 = Y − e = 4.96 − 2.0 = 2.96s t L = l1 + l 2 = 2.0 + 2.96 = 4.96s Total Lost time per cycle = L = 4.96 + 4.96 = 9.92s

38

Signal Timing and Design Example Determination of Cycle Length

Cdes =

Cdes

L

  v  c 1−   1,615  PHF  v  c  9.92 = = 32.1s  35 s 924   1−    1,615  0.92  0.9 

39

Signal Timing and Design Example

40

Signal Timing and Design Example EffectiveGreen Time Available = 35 − 9.92 = 25.08s

g A = g TOT

 VCA    VC

 470    = 25.08    = 12.76s   924  

g B = g TOT

 VCB    VC

 454   = 25.08    = 12.32s   924  

Check 12.76 + 12.32 + 9.92 = 35.0s (Cycle Length) 41

Final Signal Timings 3.6sec 1.36sec Phase 1

EW Street

NS Street

12.76sec

12.32sec

Phase 2

42

Assignment 02 Consider the intersection of two streets with two lane in each direction and relatively low turning volumes. Considering the following conditions Design the signalized intersection having moderate pedestrian activity PHF = 0.92

Target V/c = 0.90 All lanes = 20 ft Avg. Speed = 35 mph Level grades

544 621

510 432

Crosswalks = 10 ft Driver reaction time = 2.0 s

Deceleration rate = 10 ft/s-sqr

43

44