How to Design efficient Street lighting-(Part-3)


(C) Lighting Fixture:

(1) Fixture’s Mounting Height:

  • Higher mounting heights used in conjunction with higher wattage luminaries enhances lighting uniformity and typically reduces the number of light poles needed to produce the same illumination level.
  • In general, higher mounting heights tend to produce a more cost-effective design. For practical and aesthetic reasons, the mounting height should remain constant throughout the system.
  • The manufacturer’s photometric data is required to determine an appropriate mounting height.
  • Typical mounting heights for highway lighting purposes range from 30 ft to 55 ft (9.1 meter to 16.8 meter).
  • Mounting heights for light towers or High mast is typically 80 ft (24 m) or greater.
  • The installation height is too low, the glare of the lamp increases.
  • As the installation high increase, glare decreases, but the lighting utilization rate decreases.

 

(2) Fixtures Classification:

  • The Illuminating Engineering Society of North America (IESNA, IES or BIS1981) provides classifications for luminaires according to their glare control and high-angle brightness.

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(A) Full Cutoff (F):

  • A luminaire light distribution is designated as full cutoff (F) when Zero intensity at or above horizontal (90° above nadir) and Less than 10% of lamp lumens at or above 80°.
  • Full-cutoff fixtures reduce glare dramatically and eliminate direct up light by sending all their light toward the ground .This efficiency should translate into lower bulb wattages if the existing poles are used. However, some lighting engineers believe that to achieve the same illumination uniformity as their semi-cutoff counterparts, full-cutoff fixtures need to be mounted either on taller poles or closer together
  • Benefits:
  • Limits spill light on to adjacent property, reduces glare. No light is emitted directly from the luminaries into the sky.
  • Reduce Lighting Pollution.
  • Limitations:
  • May reduce pole spacing to maintain uniformity and increase pole and luminaire quantities.
  • Application:
  • Use for roadway, parking, and other vehicular lighting applications. Minimizes glare and light pollution and light trespass.

 (B) Cutoff (C):

  • A luminaries light distribution is designated as cutoff (C) when Less than 2.5% Intensity at or above horizontal (90° above nadir) and Less than 10% of lamp lumens at or above 80°.
  • The direction of maximum intensity may vary but should be below 65º.
  • Benefits:
  • Small increase in high-angle light allows increased pole spacing.
  • Cutoff system is the reduction of glare.
  • Limitations:
  • May allow some up light (Sky Light) from luminaries. Typically a small overall impact on sky glow.
  • Application:
  • Interchange lighting and rural intersections due to the ability to reduce glare.
  • Use in applications where pedestrians are present. Provides more vertical illuminance than Full Cutoff luminaires.
  • Lamp rating should be less than 3200 lumens.
  • The cutoff design is where the luminaire light distribution is less than 25,000 lm at an angle of 90° above nadir (vertical axis) and 100,000 lm at a vertical angle of 80° above nadir.

 (C) Semi Cutoff (S) (Medium Beam Angle):

  • A luminaire light distribution is designated as Semi cutoff (S) when Less than 5% Intensity at or above horizontal (90° above nadir) and Less than 20% of lamp lumens at or above 80°.
  • The direction of maximum intensity may vary but should be below 75º.
  • Benefits:
  • High-angle light accents taller vertical surfaces such as buildings. Most light is still directed downward.
  • Limitations:
  • Little control of light at property line.
  • Potential for increased glare when using high wattage luminaries. Typically directs more light into the sky than cutoff.
  • Application:
  • Used for standard road lighting. Adequate glare control is obtained with reasonable spacing.
  • The principal advantage of the semi-cutoff system is a greater flexibility in sitting.
  • Use in pedestrian areas. If using in residential areas, provide with house side shields to minimize light trespass. Lamp rating should be less than 3200 lumens.
  • For the semi-cutoff design, the luminous flux numbers become 50,000 lm for 90° above nadir and 200,000 lm at a vertical angle of 80° above nadir.
  • Semi-cutoff fixtures create broad cones of light that permit wide spacing between poles. But such fixtures create harsh glare and send some light directly into the sky.

(D) Non Cutoff (N) (Higher Beam Angle):

  • A luminaries light distribution is designated as Non Cutoff (N) when Emit light into all directions.
  • No limitations on light distribution at any angle.
  • There is considerable output near the horizontal plane.
  • Benefits:
  • Uniform luminous surfaces such as internally illuminated signs or globes. Wattage should be limited. Suitable for sports lighting, facade, landscape or other applications where luminaires are tilted due to limitations in pole or fixture locations
  • Limitations:
  • Location and aiming are critical. Most likely of all categories to produce offensive brightness and sky glow.
  • Application:
  • Used in areas with a lot of background light. Non-cutoff luminaries shall not be used at lower mounting heights because of glare.
  • Use for decorative applications only. Lamp rating should be less than 3200 lumens.
  • “Full cut off” fixtures must be installed properly, so that the bottom of the fixture is level with the ground.
  • “Fully Shielded” fixtures do not allow any light to be emitted above the lowest light emitting
  • part, but do not restrict light output in the “glare” zone, 90-80 degrees below horizontal.

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  (3) Fixtures Distributions (Optical System):

  • The Illuminating Engineering Society classified series of Fixture distribution patterns as Types I, II, III, IV, and V.

1

(A) Type I (Two-way):

  • The lateral distribution having a preferred lateral width of 15 degrees in the cone of maximum Lumen.
  • Illumination Pattern: Narrow, symmetric luminance pattern.
  • Fixture Location: This type is generally applicable to a luminaire location near the center of a roadway where the mounting height is approximately equal to the roadway width.
  • Type of Road: The luminaire is placed on the side of the street or edge of the area to be lighted. Most 1or 2 Lane Road

(B) Type II (Two Way) :

  • Light distributions have a preferred lateral width of 25 degrees.
  • Illumination Pattern: Slightly wider illuminance pattern than Type I.
  • Fixture Location: They are generally applicable to luminaires located at or near the side of relatively narrow roadways, where the width of the roadway does not exceed 1.75 times the designed mounting height.
  • Type of Road: The luminaire is placed on the side of the street or edge of the area to be lighted. It produces a long, narrow, oval-shaped lighted area which is usually applicable to narrower streets.

(C) Type III (Bat Wing) :

  • Type III light distributions have a preferred lateral width of 40 degrees.
  • Illumination Pattern: It produces an oval-shaped lighted
  • Fixture Location: This distribution is intended for luminaires mounted at or near the side of medium width roadways, where the width of the roadway does not exceed 2.75 times the mounting height.
  • Type of Road: The luminaire is placed on the side of the street or edge of area to medium width streets.

(D) Type IV (Forward throw “Asymmetric”):

  • Type IV light distributions have a preferred lateral width of 60 degrees.
  • Illumination Pattern: Widest luminance pattern.
  • Fixture Location: This distribution is intended for side-of-road mounting and is generally used on wide roadways where the roadway width does not exceed 3.7 times the mounting height.
  • Type of Road: very wide roadway (4 to 6 Lane)
  • Applications: Type IV often use at perimeters where Spill Light is required and there is no place to add Pole.

(E) Type V:

  • Type V light distributions have a circular symmetry of candlepower that is essentially the same at all lateral angles.
  • Illumination Pattern: It produces a circular, wider lighted area and is usually applicable to wide streets.
  • Fixture Location: The luminaries are mounting at or near center of roadways, center islands of parkway, and intersections.
  • Type of Road: very wide roadway (4 to 6 Lane)
  • Applications: Type V often applies to high-mast lighting.

GUIDE FOR LUMINAIRE LATERAL LIGHT TYPE AND PLACEMENT

Pole Arrangement Road Width Type of Distribution
One Side or Staggered up to 1.5 x Mounting Height Types II-III-IV
Staggered or Opposite Beyond 1.5 x Mounting Height Types III & IV
Center of the Roadway Mounting up to 2 x Mounting Height Type I

 

Type of Classification

AREA CLASSIFICATION  CUTOFF TYPE
Commercial Full Cutoff or Semi Cutoff
Intermediate Full Cutoff or Semi Cutoff
Residential Full Cutoff

 

THE SELECTION OF LUMINAIRE MOUNTING HEIGHTS

Lamp Lumens Mounting Height
≤20,000 Lumen  ≤35 Foot
20,000 To 45,000 Lumen 35 To 45 Foot
45,000 To 90,000 Lumen 45 To 60 Foot

 

Type of LED Luminaries Type of Road Lamp mounting height from the floor level (Meters) Minimum Illumination Level (Lux) at centre of road Color of Illumination
250-260W Above 18 (20 To 22) 5000K-6500K
190W A1 Between 11 To 15 (20 To 22) 5000K-6500K
140-170W A1 Between 9 To 15 (18 To 20) 5000K-6500K
90-120W A2/B1 07 To 11 (15 To 18) 4300K-5600K
70-120W A2/B1 07- To 11 (15 To 18) 4300K-5600K
70-120W B1/B2 06 To 09 (15 To 18) 4300K-5600K
70-50W B1/B2/C1 7 To 9 (12 To 15) 4300K-5600K
45-50W B1/B2/C1 5 To 7 (12 To 15) 4300K-5600K
25-30W B1/B2/C1 5 To 7 (10 To 12) 4300K-5600K

 

Relationship between mounting height and spacing

Mounting Height Width of road 6 Meter to 7 Meter 9 Meter to 10.5 Meter 12 Meter to 14 Meter
Pole  arrangement Cut-off Type Semi Cutoff Type Cut-off Type Semi Cutoff Type Cut-off Type Semi Cutoff Type
8 Meter Single side 24 28
Staggered 24 28
Opposite 28 28
10 Meter Single side 30 30
Staggered 35 35 30 35
Opposite 35 40 30 35
12 Meter Single side 42 48 36 42
Staggered 36 42 36 42
Opposite 42 48 42 48

 

GUIDE FOR LUMINAIRE LATERAL LIGHT TYPE AND PLACEMENT

SIDE OF THE ROADWAY MOUNTING            CENTER OF THE ROADWAY MOUNTING
One Side
or Staggered
Staggered
or Opposite
Local
Street Intersection
Single Roadway Twin Roadways
(Median Mounting)
Local
Street Intersections
Road Width up to 1.5 x Mounting Height Road Width beyond1.5 x Mounting Height Road Width up to 1.5x Mounting Height Road Width up to 2x Mounting Height Road Width up to 1.5x Mounting Height (each pavement) Width up to 2.0x Mounting Height
Types Types Type Type Types Types
II, III, IV III & IV II (4-way) I II & III I (4-way) & V

 

How to Design efficient Street lighting-(Part-2)


(2) Proper Placement of Pole:

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(A) Setback

  • Set back is the horizontal distance between the face of a light pole and the edge of traveled way.
  • Placing luminaries too close to a vertical surface results in hotspots at its base.
  • A setback of 3 foot to 4 foot works well for many applications.
  • Light from luminaires at extremely short setbacks grazes the surface and enhances its texture.
  • Light from luminaries at Long setbacks (Luminaries too far from a vertical surface) cause shadows at low levels.
  • Longer setbacks may be required for taller surfaces.
  • Scallops between fixtures become more noticeable as setback increases.
  • As setback (or spacing) distance increases, Light levels and uniformity decrease.

Set Back (BS 5489)

Design Speed Pole Set Back
50 Km/Hr 0.8 Meter
80 Km/Hr 1 Meter
100 Km/Hr 1.5 Meter
120 Km/Hr 1.5 Meter

(B) Overhang

  • Overhang is the horizontal distance between the center of a luminaries mounted on a bracket (Nadir) and the adjacent edge of a carriage way or traveled way.
  • In general, overhang should not exceed one fourth of the mounting height to avoid reduced visibility of curbs, obstacles, and footpaths.

(C) Outreach

  • Outreach is the horizontal distance between the center of the column and the center of the luminaries and is usually determined for architectural aesthetic considerations.

(D) Pole Boom(Arm) Length:

  • The use of an arm places the light source closer to the traveled way while allowing the pole to be located further from the edge of the traveled way.
  • Depending on the application, Pole arms may be single and/or double mast arms or davit arms at the top of the pole.
  • There are several different arm lengths and styles of arms that are used.
  • Arm Type:
  • Type A bracket an arm has a single member arm. It is used when the Arm length is less than 3.5 Meter.
  • Type B bracket arm has a two member truss arm design. Type B arms are used when the Arm length is more than 3.5 Meter.
  • Arm Lengths:
  • The length of the bracket arm is dependent upon a street width, pole location in relation to the curb and the presence of a median.
  • Type A (Single member bracket) arms are available in 2 Meter and 2.5 Meter lengths.
  • Type B (Twin member bracket) arms are available in 3.5 Meter, 4 Meter and 5 Meter Lengths.
  • Pole Height is 10 Meter: On typical streets that are 12 Meter’ wide from curb to curb, either a 2 Meter or 2.5 Meter arm is used. Depending on whether the pole is located behind the sidewalk or in the grass parkway between the sidewalk and the curb, the arm length may need to be increased to 4 Meter.
  • Pole Height is 13 Meter: On an undivided street, generally Meter, 2.5 Meter or 4 Meter arms are used.
  • Pole Height is 13 Meter: divided Street, typically have a 8 Meter wide center median to divide opposing lanes of traffic. On streets where the light poles are installed in a raised median, two 4 Meter arms oriented 180° apart are used.

(E) Boom Tilt Angle (Boom Angle)

  • When the angle of tilt is larger, a uniformity ratio is increasing. Otherwise discomfort glare is increasing because strong light comes into driver’s eyes. So the angle of tilt shall be kept from 15° to 30°.
Tilt Angle
Pole Height Arm Length Arm Tile Angle
6 Meter 0.5 Meter 5°,10°,15°
8 Meter 1 Meter 5°,10°,15°
10 Meter 1.5 Meter 5°,10°,15°
>=12 Meter 2 Meter 5°,10°,15°

(F) Pole Height:

  • Light poles for conventional highway lighting applications support luminaire mounting heights ranging from approximately 30 ft to 50 ft (9.1 m to 15.2 m).
  • Light towers for high-mast lighting applications generally range from 80 ft to 160 ft (24.4 m to 48.8 m) and are designed in multiple sections.
  • Weathering steel is a common material choice for light towers.
  • Ornamental light Poles used for local streets generally range in height for 8 ft to 15 ft (2.4 m to 4.5 m).
Pole Height Application
< 6 Meter Majority of side streets or alleys, Public gardens and parking Area to make people feel safe
8 Meter Urban traffic route , the multiplicity of road junctions
10 Meter Urban traffic routes
12 Meter Heavily used routes
18 Meter High mast lighting poles shall be installed at large-scale area such as airports, dockyards, large industrial areas, sports areas and road Intersections.

 (G) Poles distance from Curb (Offset):

  • The lighting poles should not be installed very close to the pavement edge, because the capacity of the roadway is decreased and the free movement of traffic is obstructed.
  • For roads with raised curbs (as in urban roads) =Min. 0.3 meter and desirable 0.6 meter from the edge of raised curb.
  • For roads without raised curbs (as in rural roads)=Min. 1.5 meter from the edge of the carriageway, subject to min. 5.0 meter from the center line of the carriageway.
  • Height and overhang of mounting
  • The glare on eyes from the mounted lights decreases with increases in the height of mounting. Usually, mounting height range from 6 to 10m.
  • Overhangs on the lighting poles would keep the poles away from the pavement edges, but still allow the lamp to be held above the curb or towards the pavements.

 (H) Pole to Pole Spacing

  • Spacing is the distance, measured along the center line of the road, between successive luminaries in an installation.
  • To preserve longitudinal uniformity, the space height ratio should generally be greater than 3.
  • Placing luminaries too far apart creates scallops at the base of the surface.
  • Spacing distances that are equal to 3 to 4 times the setback work well for many applications.
  • Placing luminaries closer together eliminates scallops.
  • Uniformity and light levels increase as spacing (or setback) distances decrease.
  • Spacing of luminaires normally does not exceed five to six mounting heights.
  • The span must not be more than 45 meters and for an average of 20-30 meters.

Lighting Pole details as per Road

Road Road Width (Meter) Pole Arrangement Lamp (Watts) Pole to Pole Spacing (Meters) Mounting Height, (Meters) Arm Length, (Meters)
Expressway 10 Twin Central 250 25 To 35 12 1.5
15 250 20 To 35 12 3.0
20 Opposite 250 20 To 45 12 1.5
25 250 20 To 40 12 1.5
30 250 20 To 30 12 1.5
36 250 20 To 25 12 1.5
40 250 20 To 22 12 1.5
Major 10 One-side 250 10 To 40 10 1.5
15 250 10 To 45 12 3.0
10 Twin Central 150 20 To 37 10 1.5
15 250 20 To 43 12 3.0
20 Opposite 150 20 To 40 10 3.0
25 250 20 To 45 10 1.5
30 250 20 To 45 10 1.5
36 250 20 To 45 12 3.0
40 250 20 To 45 2 3.0
Collector 10 One-side 150 10 To 40 10 1.5
15 250 10 To 50 12 3.0
10 Twin Central 150 20 To 40 10 1.5
15 150 20 To 37 12 3.0
20 Opposite 150 20 To 47 10 1.5
25 250 20 To 48 10 1.5
Rural
Highway
8 One-side 150 10 To 38 8 1.5
10 150 10 To 37 8 3.0
15 150 15 To 38 10 3.0
10 Twin Central 150 20 To 45 10 3.0
15 150 20 To 39 12 3.0
20 1.5
Minor 4 One-side 70 10 To 40 8 1.5
6 70 10 To 40 8 1.5
8 70 10 To 40 8 1.5
10 70 10 To 39 8 1.5
10 Twin Central 70 20 To 35 8 1.5
15 Staggered 70 10 To 20 8 1.5
15 Opposite 70 20 To 40 8 1.5

 

Illumination Level
Classification  Average Illumination (lux) Ratio Minimum to average illumination
Class A1 30 0.4
Class A2 15 0.4
Class B1 8 0.3
Class B2 4 0.3

 

Relationship between Mounting Height and Spacing of Fixtures

Pole Arrangement Cut-off type Semi cutoff type
Height Spacing Height Spacing
Single side >=0.7 X Width of Road <=3 X Fixture Mounting Height >=0.8 X Width of Road <=3.5 X Fixture Mounting Height
Both Side Staggered >=1.5 X Width of Road <=3.5 X Fixture Mounting Height >=1.7 X Width of Road <=4 X Fixture Mounting Height
Both Side Opposite >=0.5 X Width of Road <=3 X Fixture Mounting Height >=0.6 X Width of Road <=3.5 X Fixture Mounting Height
Twin central >=0.7 X Width of Road <=3.5 X Fixture Mounting Height >=0.8 X Width of Road <=4 X Fixture Mounting Height

 

 Pole to Pole Distance vs Lux Level

Pole Height Lamp Pole to Pole Distance Max. Illumination (Lux) Average (Lux)
4 Meter 15 watt 12 to 18 Meter 25 18
5 Meter 18 watt 14 to 20 Meter 30 18
6 Meter 30 watt 18 to 24 Meter 32 20
7 Meter 50 watt 21 to 28 Meter 32 20
8 Meter 100 watt 24 to 32 Meter 40 22
9 Meter 110 watt 27 to 35 Meter 34 20
10 Meter 140 watt 30 to 40 Meter 35 22
12 Meter 180 watt 30 to 40 Meter 33 23
14 Meter 200 watt 30 to 40 Meter 30 21

 

Lux Vs Mounting Height

Fixtures (Lux) Mounting Height
3000 to 10000 Lux 6 to 7 Meter
10000 to 20000 Lux 7 to  9 Meter
More than 20000 Lux More than 9 Meter

 

 
Road Road Type Type of Pole positions Individual Carriageway Width (Meter) Central Verge (Meter) Pole Height above Ground (Meter) Maximum Pole to Pole Spacing (Meter) Clearance from Road Edge (Meter) Bracket Length (Meter) Tilt Angle Lighting Specifications Lamp (Watt)
A1 Dual Carriage Central Verge 10 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 11 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 12 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 14 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Dual Carriage Central Verge 16 1.2 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 12 0 12 35 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 250W
A1 Single Carriage Opposite 14.5 0 12 35 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 250W
A1 Single Carriage Opposite 16 0 12 40 0.6 Around one meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 18 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 21 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
Single Carriage Opposite 25 0 12 40 0.6 1 meter  10° 35 lux
/0.4/ 0.33
HP SV 400W
A1 Single Carriage Opposite 31 0 12 40 0.6 1 meter  10° 35 lux/ 0.4/
0.33
HP SV 400W
A2 Single Carriage Single Sided 10 11 30 0.6 < 1.0 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 9 11 30 0.6 < 0.5 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 7 11 30 0.6 < 0.5 meter  10° 25 lux
/0.4/ 0.33
HP SV 250W
A2 Single Carriage Single Sided 7 11 30 0.6 < 0.5 meter  10° 25lux
/0.4/ 0.33
HP SV 250W
A3 Single Carriage Single Sided 7 8 20 0.6 < 0.5 meter  10° 20lux
/0.4
HP SV 150W
Pedestrian Pathway Single Carriage Single Sided 3m-6m 7.5 20-25 0.6 <0.5 meter  10° 20 lux
/0.4
HP SV 150W

 

Poles (Meter) Top Dia (mm) Bottom Dia (mm) Thickness (mm) Base plate (mm) Single Arm Bracket (mm) Double Arm Bracket (mm)
3 70 130 3 200x200x12 1000 NA
3 70 130 3 200x200x12 NA 1000
4 70 130 3 200x200x12 1000 NA
4 70 130 3 200x200x12 NA 1000
4 70 130 3 200x200x12 1000 NA
5 70 130 3 200x200x12 NA 1000
5 70 130 3 200x200x12 1000 NA
6 70 130 3 200x200x12 NA 1000
6 70 130 3 200x200x12 1000 NA
7 70 135 3 225x225x16 1000 NA
7 70 135 3 225x225x16 NA 1000
8 70 135 3 225x225x16 1000 NA
8 70 135 3 225x225x16 NA 1000
9 70 155 3 260x260x16 1000 NA
9 70 155 3 260x260x16 NA 1000
9 70 175 3 275x275x16 1000 NA
9 70 175 3 275x275x16 NA 1000
10 70 175 3 275x275x16 1000 NA
10 70 175 3 275x275x16 NA 1000
10 70 200 3 290x290x16 1000 NA
10 70 200 3 290x290x16 NA 1000
11 70 210 3 320x320x20 1000 NA
11 70 210 3 320x320x20 NA 1000
12 70 230 3 325x325x20 1000 NA
12 70 230 3 325x325x20 NA 1000

 

Recommended Levels of Illumination (BIS 1981) (IS 1944)

Type of Road Road Characteristics Road Width (Meter) Average Level of Illumination on Road Surface in Lux Ratio of Minimum/Average Illumination Ratio of Minimum/Max Illumination Type of Luminaire Preferred Luminas Mounting Height
A-1 Important traffic routes carrying fast traffic >10.5,12,14,16,18,20,30 30 0.4 33 Cutoff 9 To 10 Meter
A-2 Main roads carrying mixed traffic like city main roads/streets, arterial roads, throughways > 7 m up to 10 m 15 0.4 33 Cutoff 9 To 10 Meter
B-1 Secondary roads with considerable traffic like local traffic routes, shopping streets < 7m Colony Roads 8 0.3 20 Cutoff or semi-cutoff 7.5 To 9 Meter
B-2 Secondary roads with light traffic 4m,5m, 6m 4 0.3 20 Cutoff or semi-cutoff 7.5 To 9 Meter

 

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