TRANPORTATION LIGHT MANAGEMENT
*** Content:
1-Benefits & fundamentals of Lighting
2-Facility & area classifications
3-Roadway lighting considerations
4-Tunnel lighting
5-Types of luminaries
6-Safety & supports
7-Pole types
8-Foundations & bases
9-Post-construction
10-Refrences
1-Benefits & fundamentals of Lighting
Properly designed and installed roadway lighting can result in significant reductions in nighttime traffic accidents, act as a deterrent to crime, increase commercial activity, and improve aesthetic value.
Roadway lighting increase traffic safety by enhancing the visibility of potential roadway hazards, other vehicles, pedestrians, and roadway geometrics.
Pedestrians are among the largest beneficiaries of lighting installed on urban streets.
Studies indicate reductions of up to 80% in pedestrian accidents and reductions ranging from 20% to 40% for all types of night accidents.
Roadway lighting has been recognized as a viable countermeasure for increasing traffic safety since 1966.
The benefits of providing roadway lighting include:
Enhancing traffic safety
Improving pedestrian visibility
Deterring crime
Improving commercial interests
Promoting community pride
The actual benefits obtained are dependent upon the type of facility and area in which the lighting will be installed.
***Note:
Lighting cannot, however, be
expected to achieve the same
safety levels as day time operation,
because of the influence of other
factors, such as:
Fatigue
Higher speeds
Intoxication, which make a greater contribution to night time accident frequency.
Visibility: Luminance & Illuminance
The requirement of adequate visibility is essential for safe traffic operations during both day and night operation.
Visibility can be separated into at least 3 classifications when applied to highway driving:
Perception
Recognition
Decision making
Illuminance is a measure of the amount of light that falls upon a roadway surface (horizontal footcandle-candles per square ft-or lux) and also measured in candles per square meter(cd/m^2)
Warranting conditions:
The potential traffic safety benefits of lighting are due to an increase in driver comfort and confidence resulting from enhanced vision.
This reduces driving stress and tension, increases roadway capacity, and reduces the potential for traffic accidents.
Warranting conditions are based on minimum conditions which signify that providing lighting would be beneficial.
Local conditions such as frequent fog, ice, snow, roadway geometry, ambient lighting, sight distance, and signing could justify modifying the warrants either positively or negatively.
Judgment on lighting need should include assessment of the anticipated benefits, traffic volume, speed, road use during the night, night accident rate, road geometrics, and general night visibility.
2-Facility & area classifications
Facility types:
Freeway: A divided major roadway with full control of access
Expressway: A divided major arterial highway
Major: Serves as the principal network for through-traffic flow
Collector: Serves traffic between major and local streets
Local: For direct access to residential, commercial, industrial regions
Alleys: A narrow public way
Sidewalks: For pedestrian use
Pedestrian ways: Skywalks (overpasses), Subwalks (tunnels)
Bicycle lanes: For bicycle travel
Area classification:
Vehicle/Pedestrian interaction
3 classification of pedestrian night activity levels and types of land use:
High: Areas with significant numbers of pedestrians, e.g. downtown retail areas and areas near theaters, concert halls, stadiums, and transit terminals.
Medium: Areas where lesser number of pedestrians utilize the streets at night, e.g. downtown office areas, blocks with libraries, apartments, and neighborhood shopping, industrial area, older city areas, and streets with transit lines.
Low: Areas with low volume of night pedestrian usage, e.g. suburban single-family streets, very-low-density residential developments, and rural or semi rural areas.
As a guide:
1-h pedestrian counts, during the first hour of darkness.
Low 10 or fewer
Medium 11 to 100
High over 100
3-Roadway lighting considerations
Freeway lighting considerations
Freeway lighting can substantially: reduce accident frequency and increase capacity.
A list of the specific conditions:
1-Warranting conditions for continuous freeway lighting:
*Case CFL-1: On those sections in or near cities where the ADT (Average Daily Traffic) is 30,000 or more.
*Case CFL-2: Where three or more Successive interchanges are located with an average spacing of 1.5 mi(2.4 km) or less adjacent outside the right-of-way are substantially urban.
*Case CFL-3: where for a length of 2 mi(3.25 km) or more the freeway passes through a developed suburban area.
*Case CFL-4: Where the ratio of night accidents to day is at least 2 for all unlighted similar sections.
2-Warranting conditions for complete interchange lighting:
*Case CIL-1: Where total current ADT ramp traffic entering and leaving the freeway within the interchange area exceeds 10,000 for urban conditions, 8,000 for suburban conditions, or 5,000 for rural conditions.
*Case CIL-2: Where current ADT on the crossroad exceeds 10,000 for urban conditions,8,000 for suburban conditions, or 5,000 for rural conditions.
*Case CIL-3: Where existing substantial commercial or industrial development, which is lighted , is located in the immediate vicinity of the interchange; or where the crossroad approaches are lighted for at least 0.5 mi on each side of the interchange.
*Case CIL-4: Where the ratio of night accidents to day accidents within the interchange area is at least 1.5 times higher than the average for all unlighted similar interchanges.
3-Warranting conditions for partial interchange lighting:
*Case PIL-1: Where the total current ADT ramp traffic entering and leaving the freeway within the interchange area exceeds 5,000 for urban conditions, 3,000 for suburban condition, or 1000 for rural conditions.
*Case PIL-2: Where the current ADT on the freeway through traffic lanes exceeds 25,000 for urban conditions, 20,000 for suburban conditions, or 10,000 for rural conditions.
*Case PIL-3: Where the ratio of night accidents to day accidents within the interchange area is at least 1.25 times higher than the average for all unlighted similar interchanges.
4- Special conditions:
Where there is continuous freeway lighting, there should be complete interchange lighting.
Ramps, bridges and overpasses should be lighted as the same level as the main roadway.
The point of least illuminance on the roadway should not be less than 2 lux.
The higher levels of illuminance should be at the gores and intersections.
Streets and Highways other than Freeways:
Traffic volume, numbers of pedestrians, turning movements, signalization, and unusual geometrics are some elements that make lighting of streets and highways desirable.
Warranting conditions for roadways other than Freeways:
It’s not practical to establish specific warrants for the installation of roadway lighting to satisfy all prevailing or anticipated conditions.
In general, lighting may be considered for those locations where the respective governmental agencies concur that lighting contributes substantially to the efficiency, safety, and comfort of vehicular or pedestrian traffic. Lighting may be provided for all major arterials in urbanized areas.
It may also be provided for locations or sections of streets and highways where the ratio of night accidents to day accidents is high.
Roadway rest areas:
The design of lighting for rest requires consideration of both vehicle and pedestrian needs.
The lighting concerns for rest areas can be divided into several distinct areas:
Entrance and exit
Interior roadways
Parking area
Activity area
***************************************Rest areas are often located in remote areas that are not readily accessible by bucket trucks or other special maintenance equipment. This requires that lighting system components be selected that provide maximum protection again vandalism and require minimal maintenance.
4-Tunnel lighting
Design of tunnel lighting requires adaptation for driver needs in the approach, and threshold, transition, and interior zones. Tunnels are classified by structure length and geometric alignment.
Lighting adaptation zones for tunnel lighting:
Approach: The external roadway area leading to the tunnel.
Portal: The plane of entrance into the tunnel
Threshold zone: The area inside the tunnel where a transition is made from the high natural lighting level to the beginning of the transition zone
Transition zone(s): Areas that allow the motorist to achieve appropriate eye adaptation by incrementally reducing the level of luminance required in the threshold zone to the luminance of the interior zone.
Interior zone: Area within the tunnel after eye adaptation has been completed.
5-Types of luminaires
Cobra head luminaires
High mast luminaires
Offset luminaires
Segmented reflector luminaires
Cobra head luminaires:
Conventional roadway lighting has been the cobra head luminaire mounted on a support arm and positioned at the edge of the roadway or out over the roadway.
Cobra head luminaires are available in a wide range of full cutoff, semicutoff, and noncutoff beam patterns
All Cobra head luminaires have a horizontal lamp position that caused them to provide a large amount of light directly under the luminaire.
High mast luminaires
They are designed to be mounted on the lowering ring of high mast pole.
The beam patterns are referred to as long and narrow, and symmetrical and nonsymmetrical, cutoff and noncutoff types are used.
High mast luminaires considerations:
The value of them has been highly controversial since their introduction in the early 1960s.
Proponents suggested that high mast luminaires offered considerable enhancements to visibility.
Opponents, on the other hand, argued that high mast luminaire was expensive to build, offered little improvement to visibility, and often resulted in light trespass and light pollution.
The value of high mast luminaires:
By the early 1980s, new data became available which suggested the superiority of high mast light over conventional systems:
Improves luminance uniformity
Improved visual field
Removes luminaires from driver’s active viewing area
Better location for reduction in the number of vehicular collision with fixed objects
Fewer luminaires and less energy
***************************************
High mast systems also offer advantages in cases where future road widening is excepted.
Offset luminaires:
When high mast poles can not be located in the middle of the area to be lighted , is to specify an offset-type luminaire mounted on the high mast lowering ring in lieu of the “traditional” high mast luminire. This produces a more directional pattern that can reduce the amount of off-premise light.
***************************************
Segmented reflectors luminaires:
They are special-purpose luminaires that have been successfully used on top of concrete median barriers.
6-Safety & supports
The primary purpose of roadway illumination is to increase safety by enhancing night time visibility.
The net safety benefit from increased visibility is influenced by the hazard posed by the roadway lighting or luminaire support acting as a fixed object. If roadway illumination is not warranted, or if it is installed wrong, there is a strong possibility that traffic hazards will be increased rather than reduced by providing illumination. Safety should be enhanced by considering the following:
Remove the hazard from the right-of-way
Locate the hazard in place less likely to be struck
Provide a breakaway support
Provide a barricade
Luminaire supports:
Approximately 15% of all fixed-object fatalities involve sign and luminaire supports or utility poles.
The options available to the highway engineer to improve them are:
Remove or redesign, relocate, use a breakaway device, shield, or delineate
***************************************From a roadside safety perspective, a preferred method for lighting major intersections is to use high mast lighting, because fewer supports are required and they can be located farther from the roadway.
7-Pole types
Poles are available in a number of materials:
Steel (galvanized, painted, powder-coated, and weathering types, etc): low cost & extended life
Aluminum: resistance to corrosion
Stainless steel: corrosion-resistant and relatively light weight
Fiberglass: fiberglass-reinforced plastic (FRP)
Wood: the least expensive of pole type
Concrete
8-Foundations & bases
Foundations:
The foundation for a luminaire pole must provide sufficient resistance to overturning moments caused by the static load of the mast arm plus a wind and/or an ice load. It must be capable of maintaining the correct alignment of the luminaire and able to withstand the impact should the pole be struck.
Bases:
Breakaway luminaire poles are designed to yield at their base attachment to the foundation. There are numerous types of bases currently in service.
A list of the most common base types:
Direct burial base: It allows the pole to be directly embedded in the soil. It is most economical, since it eliminates the need for foundation.
Flange base: For most steel and aluminum poles
Cast-Aluminum transformer base (T-base): May be steel or cast-aluminum and were originally divided to house the transformer.
Frangible couplings: The typical coupling is a short connector attached to the foundation.
Slip base: To resist and vibration loads
Shear base: To load the rivets or welds
that secure the base to a foundation plate.
9-Post-construction
Acceptance tests:
Insulation tests
Ground resistance test
High mast lowering test
Photo controller test
Voltage tests
***************************************Maintenance conditions:
Maintenance must be considered from the earliest design stages of a lighting project.
After a system is installed and tested for operate and for component integrity, proper maintenance procedures can produce continual high performance of the roadway lighting system.
10-Refrences
References of this research:
1-Highway Engineering Handbook (2nd Edition)
[Roger L. Brockenbrough & Kenneth J. Boedecker,Jr]
MC Graw-Hill 2003 (6th & 7th chapter)
www.books.mcgraw-hill.com
2-www.iesna.org
3-www.pbase.com/streetscape/lights
4-www.venturelighting.com
5-www.benesch.com/web/roadwaylighting.html