IRC Method of Signal Design

Design of traffic signals as per IRC specifications are explained

1. TRAFFIC SIGNAL DESIGN [IRC 93-1985]

2. A traffic control device whether manually, electrically or mechanically operated, by which traffic is alternately directed to stop and proceed in a specified direction Fixed time signals Vehicle actuated signals Semi-vehicle actuated signals

3. Green signal – traffic except pedestrians may cautiously enter the intersection to make movement indicated by GREEN ARROWS Steady Amber Signal – warn that green movement is being terminated or red indication will be immediately exhibited Steady Red Signal – traffic shall stop at a clearly marked stop line

4. Flashing Red ( STOP signal) Driver shall stop vehicle at STOP line to have a view of approaching traffic on intersecting roadway prior to entering the intersection Right to proceed is subjected to availability of safe gap Flashing Amber ( CAUTION signal) Drivers may proceed through the intersection with caution

5. Pedestrian Signal (1) Steady Green (2) Flashing Red (3) Steady Red Proceed across roadway on the cross-walk Pedestrians already on the carriageway shall quickly proceed to nearest refuge island or footpath and those on footpath or island shall not enter the roadway Pedestrians shall not enter roadway

6. Size & Design Signal Lenses Circular Diameter - 200 or 300 mm 300 mm diameter is used in intersections such as :- Suburban area with 85 th percentile speed > 70kmph Busy urban area with 85 th percentile speed > 50kmph 3 lane approaches & locations with conflicting or competing background lighting in urban areas

7. Lens of same colour arranged horizontally to each other at right angles to basic straight line Should be clearly visible to drivers, from atleast 400m under normal atmospheric condition Influence of curves, grades, obstructions and distance required to stop the vehicle from an average approach speed should be considered in directing and locating signals

8. Location & number of signal faces Minimum of two signal faces for through traffic shall be provided One of them shall be erected on near side of intersection (primary) & other on far side (secondary) If visibility is obstructed, a suitable sign, supplemented by a flashing amber shall be erected in advance to warn driver about approaching traffic

9. Atleast one signal face over the travelled roadway for each approach Supports for post-mounted signal heads at the side of street with kerbs shall have a horizontal clearance of not less than 60 cm

10. Height of signal face Bottom of signal face shall be 2.5m above footpath or crown of the roadway For signals suspended over a roadway, height shall be 5.5m above crown Maximum height of bottom of post-mounted signal face shall not exceed 4.6m & in case of over-head signal face, it shall not exceed 5.8m

11. Maintenance Provide alternate operation of signal during failure Properly skilled maintenance staff shall be available without undue delay for emergency (lamp failures) Maintain appearance of signal installation If controller fails, it shall automatically change over to flashing amber or turn off all signals Paint signal post & housing with yellow for best contrast with background Provide auxiliary signs (turn restrictions) Remove unauthorized sign, advertisement, signal, marking or devices

12. Warrants

13. Traffic and engineering data required Number of motorized vehicles entering the intersection in each hour from each approach containing greatest percentage of 24 hours traffic Classified vehicular volume for each traffic movement from each approach for atleast 2 hours morning & evening peak periods Pedestrian volume count on each cross walk during the same period 85 th percentile speed of all vehicles on uncontrolled approaches

14. Condition diagram showing physical features such as Intersection geometrics Channelization Grades Sight distance restrictions Bus stops and parking conditions Pavement markings, street lightings Driveways Nearby rail-road crossings Utility poles & fixtures Adjacent land use Collision diagram showing Location & direction of movement Severity & time of occurrence

15. For more precise understanding following data are also desirable :- Delay for each approach 85 th percentile speed near to intersection but unaffected by control Pedestrian delay for atleast two 30 minutes peak pedestrian delay period

16. Desirable to have adequate roadway capacity at signalized intersection Widening of main highway and intersecting roadway is warranted:- To reduce delay To reduce signal time assigned to side street traffic Additional width is necessary on leaving and approach side to clear traffic through intersection effectively Desirable to have atleast two lanes on each approach Effect of widening can be achieved by elimination of parking Before widening, additional green time required for pedestrian to cross widened road should be checked

17. Warrants for Signal Installation Any one or more of following warrants should be met for signal installation Warrant 1 – Minimum vehicular volume Warrant 2 – Interruption of continuous traffic Warrant 3 – Minimum pedestrian volume Warrant 4 – Accident experience Warrant 5 – Combination of warrants

18. Warrant 1 – Min. Vehicular Volume Traffic volume on the major street & the higher volume minor street for each of any 8 hours of an average day should be equal to as follows

19. Major street & minor street volume are for same 8 hours Each traffic lane at intersection shall be minimum 2.8 m wide If 85 th percentile speed of major street exceeds 50kmph or when intersection lies in built-up area of population less than 2.5 lakhs , then minimum vehicular volume warrant is 70% of the requirements stated in the table

20. Warrant 2 – Interruption of continuous traffic Traffic volume on the major street & the higher volume minor street for each of any 8 hours of an average day should be equal to as follows

21. This warrant is applied if operating conditions or traffic volume on major street is so heavy that traffic on minor street suffers excessive delay or hazard in entering or crossing major street If 85 th percentile speed of major street exceeds 60kmph or when intersection lies in built-up area of population less than 2.5 lakhs, then the warrant is 70% of the requirements stated in the table

22. Warrant 3 – Min. pedestrian volume For each of any 8 hours of an average day, following traffic volumes exist On the major street, 600 or more vehicles per hour enter the intersection (both approaches) or where there is a raised median island 1.5 m or more in width, 1000 vehicles per hour enter the intersection on major street During the same 8 hours, there are 150 or more pedestrians per hour on the highest volume cross-walk crossing the major street

23. If 85 th percentile speed of major street exceeds 60kmph or when intersection lies in built-up area of population less than 2.5 lakhs, then the warrant is 70% of the requirements stated Under this warrant, it is desirable to have a traffic actuated signal with push buttons for pedestrians crossing the street, at isolated intersections or mid-blocks Kerb parking prohibited for 75 m before and beyond the cross-walk Cross-walk should not be closer than 300 m to another established cross-walk

24. Warrant 4 – Accident experience Adequate trial of less restrictive remedies with satisfactory observance & enforcement have failed to reduce accident frequency Five or more reported accidents in 1 year that can be corrected by traffic signals , each accident involving personal injury or property damage to an apparent extent of Rs. 2000 or more Signal installation does not seriously disrupt traffic flow

25. Warrant 5 – Combination of warrants In exceptional cases, signals may be justified occasionally where no signal warrant is satisfied , but there where two or more of warrants 1, 2 and 3 are satisfied 80% or more

26. Functional Specifications

27. Standard controller shall provide for 6 phases with green, amber and red in each phase. Green interval shall be adjustable in steps of 2 seconds from 10 to 60 sec Amber interval shall be adjustable to either 2,3,4 or 5 sec Vehicle signal sequence Red-Amber-Green-Amber or Red-Green-Amber Initial amber Clearance amber Facility shall be provided with flickering of left turn arrows Facilities shall be provided for pedestrian crossing

28. Shall have provision for 3 cycles with different intervals in each cycle to cater morning, evening & off-peak traffic. In addition, one cycle of amber flashing on main roads & red flashing on minor road to cater to night conditions Optional facility for manual control of signal

29. Co-ordinated Signal

30. Need for coordinated signal Progressive movement to traffic in specified direction at predetermined speed To reduce delays and avoid main traffic from having to stop at every junction Objectives:- To pass maximum amount of traffic without enforced halts To have minimum overall delay both in main & side road To prevent the queue of vehicles at one intersection extending & reaching next intersection

31. Signals within 1 km of one another along major route should be operated in co-ordination Offset Difference between start of green time at successive upstream & downstream signals Offset of downstream signal shall be such that platoon has an unhindered movement Time & Distance Diagram Time & signal settings are plotted horizontally & distance travelled along major road vertically

32. Time & distance diagram for one-way street with linked signals

33. Distance (ft) Time (Cycles) Intersections 1000’ 2200’

34. Distance (ft) Time (Cycles) Intersections

35. Distance (ft) Time (Cycles) Intersections

36. Distance (ft) Time (Cycles) Intersections

37. Distance (ft) Time (Cycles) Intersections

38. Time & distance diagram for two-way street with linked signals

39. Time & distance diagram for two-way street with linked signals

40. Types Simultaneous/Synchronized System Alternate/Limited progressive system Simple progressive system Flexible progressive system

41. Simultaneous System All signals along a given street always display same indication at same time Cycle time is same at all intersections Disadvantages:- Not conducive to give continuous movement of all vehicles Encourage speeding of drivers between stops Reduce overall speed Inefficient at some intersection due to same cycle time provided for all intersections

42. Alternate System Consecutive signals display contrary indications at same time Permit vehicles to travel one block in half cycle time Efficient if blocks are of equal lengths Speeding of drivers are stopped at each signal Disadvantages:- Green times for both main & side streets have to be substantially equal, resulting in inefficiency at most of the intersections Not well suited where block lengths are unequal Adjustments are difficult for changing traffic conditions

43. Simple Progressive System Various signals display green aspects in accordance with a time schedule Permit continuous operation of platoon of vehicles at a planned rate of motion, which vary in different parts of system Offsets are fixed & cannot be altered Cycle time is different at each signal installations, but fixed Flexible Progressive System Improvement over simple progressive system Possible to introduce flashing or shut down during off-peak hour It is possible to vary the offsets Cycle time & division vary at each signal depending on traffic

44. Cycle lengths & Green period

45. Assumptions Vehicles arriving on an approach distribute equally on different lanes meant for a particular direction Number of vehicles arriving on an approach is equal in all cycles, having identical cycle lengths Reaction time to start from stop for first vehicle is 6 sec & subsequent vehicles follow a uniform headway of 2 sec

46. Pedestrian Green Green time = ( Width of carriageway to be crossed in metre divided by assumed walking speed of 1.2m/s )+ (Reaction time of 7 sec ) Optimum cycle length shall be designed such that delay at all approaches will be minimized Cycle length should be rounded to multiple of five Max recommended cycle time = 120 sec More than 4 phases in any given cycle is less preferred

47. Optimum Cycle Time Depend on traffic conditions Cycle time is longer when heavily trafficked Cycle time short  starting delays & lost time high Degree of trafficking (y) = Webster’s optimum cycle time, L – total lost time per cycle Y – sum of maximum y-values for all phases of the cycle

48. Example 2 phase, 4-arm intersection, equal flows on all arms, equal saturation flow of 1800 veh /hr, equal green times, total lost time per cycle = 10 sec n = number of phases Total Flow ( veh /h) (1) Flow per approach (2) y –value (2)/1800 (3) L (4) Y n x (3) (5) C0 3000 750 0.42 10 0.84 125 2800 700 0.39 10 0.78 91 2400 600 0.33 10 0.66 59 1600 400 0.22 10 0.44 36

49. Effect on delay of variation of cycle length

50. Example

51. Webster’s Delay Equation Average delay per vehicle (d) on a particular intersection leg is given by, C = correction factor Therefore,

52. Example

53. Thank you...