TOWN PLANNING LECTURES BY RAVINDAR KUMAR: LAYOUT OF STREET, ROAD CROSSING AND LIGHTING

AR-309: ARCHITECTURE AND TOWN PLANNING (SECTION-B)
By
RAVINDAR KUMAR
Assistant Professor
Department of Architecture and Planning
NED University of Engineering and Technology
Karachi

LECTURE NO: 25
TOPIC: LAYOUT OF STREET, ROAD CROSSING AND LIGHTING

INTRODUCTION:
The theme of current lecture is, “layout of street, road crossing and lighting”. The main purpose of this theme is to get a clear understanding about the physical features of a street along with its’ major elements. The term street itself is a very vast term and it is explained and interpreted in various ways. Similarly the characteristics of streets are also plentiful. Thus in the following all these aspects of streets shall be discussed in details.

WHAT IS STREET?
A Street is a paved public thoroughfare in the built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A Street is characterized by the degree and quality of street life it facilitates, whereas a road serves primarily as a through passage for vehicles or pedestrians.[1]

STREET FURNITURE:
‘Street furniture’[2] is a collective term for objects and pieces of equipment installed on streets and roads for various purposes, including traffic barrier, benches, bollards, post boxes, phone boxes, streetlamps, street lighting, traffic lights, traffic signs, bus stops, grit bins, tram stops, taxi stands, public lavatories, fountains and memorials, and waste receptacles. An important consideration in the design of street furniture is how it affects road safety.

STREET NAME SIGNS identify streets, for the benefit of visitors, especially postal workers and the emergency services. They may also indicate the district in which the street lies.

A BENCH is essentially a chair made for more than one person, usually found in the central part of any settlement (such as plazas and parks). They are often provided by the local councils or contributors to serve as a place to rest and admire the view. Armrests in between are sometimes provided to prevent people lying down and/or to prevent people from sitting too close to someone who likes to keep some distance.

BOLLARDS are posts, short poles, or pillars, with the purpose of preventing the movement of vehicles onto sidewalks or grass etc.

POST BOXES, also known as MAIL BOXES, are found throughout the world, and have a variety of forms: round pillar style found in Japan and the U.K. (the two feature a difference in that the Japanese version has a round lid while the UK version is flat); rectangular blue boxes in the United States; red and yellow boxes with curved tops in Australia, some on poles. The Canadian version is a red box with a slanted back top.

PHONE BOXES or TELEPHONE BOOTHS are prominent in most cities around the world, and while ranging drastically in the amount of cover they offer users, e.g. many only cover the phone itself while others are full booths, are instantly recognisable. The widespread use of mobile phones has resulted in a decrease in their numbers.

STREETLAMPS are designed to illuminate the surrounding area at night, serving not only as a deterrent to criminals but more importantly to allow people to see where they're going.

TRAFFIC LIGHTS (or TRAFFIC SIGNALS) usually include three colours: green to represent "go", amber to inform drivers that the colour will alternate shortly and red to tell drivers to stop. They are generally mounted on poles or gantries or hang from wires.

TRAFFIC SIGNS warn drivers of upcoming road conditions such as a "blind curve", speed limits, etc. Direction signs tell the reader the way to a location, although the sign's information can be represented in a variety of ways from that of a diagram to written instructions. Direction signs are usually mounted on poles. Recently, illumination has started to be added in order to aid nighttime users.

PUBLIC LAVATORIES allow pedestrians the opportunity to use restroom facilities, either for free or for a per-use fee.

STREETS TYPOLOGY:

Streets are of many types and there are different names attributed to a street. For instance street can be termed as an alley, lane, avenue, boulevard etc. In addition there are streets names such as Main Street, side streets, two way streets, numbered streets, walkways and cul-de-sacs etc. Similarly there are processes attached to streets such as traffic calming etc.

An ALLEY[3] or ALLEYWAY is a narrow, pedestrian lane found in urban areas which usually runs between or behind buildings. In older cities and towns in Europe, alleys are often what is left of a medieval street network, or a right of way or ancient footpath in an urban setting. In older urban development, alleys were built to allow for deliveries such as coal to the rear of houses. Alleys may be paved, or simply dirt tracks. Blind alleys have no outlet at one end and are thus a cul-de-sac.

Many modern urban developments do not incorporate alleys. In some locations installation of gates to restrict alleyway access have significantly reduced burglary rates. On blocks where gates are not installed, residents sometimes erect home-made barricades at alley entrances.

Alleys which are narrow pavements between/behind buildings can be known as SNICKETS, GINNELS, JENNELS or ALLEYWAYS. This has led to the word SNICKELWAY, originally in York, though the term has become more widespread.

In Sussex the term TWITTEN is commonly used whilst in Liverpool the term ENTRY or JIGGER is more common.

The word JITTY is also often used in Derbyshire and Leicestershire.

GULLEY is the term sometimes used in the Black Country.

In Karachi and Mumbai the term ‘PATLEE GALLEE’ (Narrow Street) is usually used as an admonition for cowards to runaway.

In Nottinghamshire TWICHELL is a common name.

In Scotland the terms CLOSE, WYND AND PEND are commonplace.

JENNEL is local to Sheffield.

In Glasgow, Edinburgh and Belfast, and the surrounding areas, certain alleys are known as ENTRIES, ENTRY, AND ANTRIM.

In Australia and Canada the terms LANE, LANEWAY and SERVICEWAY are also used.

In the United States and Canada alleys are sometimes known as REAR LANES or BACK LANES because they are at the back of buildings.

The word LANE[4] has several meanings and types, it can be a portion of a paved road which is intended for a single line of vehicles and is marked by white or yellow lines or a lane is a narrow road or street, usually lacking a shoulder or a median; this is typically applied to roads, but can also be applied to urban streets or areas that used to be streets.

A TRAFFIC LANE OR TRAVEL LANE is a lane for the movement of vehicles traveling from one destination to another, not including shoulders and auxiliary lanes.

A THROUGH LANE or thru lane is a traffic lane for through traffic. At intersections, these may be indicated by arrows on the pavement pointing straight ahead.

A CARRIAGEWAY is a series of lanes (or part of a road) in which vehicles travel.

A LOADING LANE is an area next to a curb, which is reserved for loading and unloading passengers. It may be marked by a "LOADING ONLY" sign or a yellow or white curb.

A TRAM LANE is a lane reserved for the use of buses, trams and taxicabs.

AN EXPRESS LANE of a road is used for faster moving traffic and has less access to exits/off ramps.

AN AUXILIARY LANE along a highway or motorway connects slip roads, with the entrance ramp or acceleration lane from one interchange leading to the exit ramp or deceleration lane of the next.

A DECELERATION LANE is a paved or semi-paved lane adjacent to the primary road or street. It is used to improve traffic safety by allowing drivers to pull off the main road and decelerate safely in order to turn, so that the traffic behind the turning vehicle is not slowed or halted. Deceleration lanes are primarily found in suburban settings.

A FIRE LANE is the area next to a curb, which is reserved for firefighting equipment, ambulances, or other emergency vehicles. Parking in these areas, often marked by red lines, usually warrants a parking ticket.

A PASSING LANE is often provided on steep mountain grades, in order to allow smaller vehicles to pass larger, slower ones. This is sometimes called a climbing lane if on the uphill side. Passing lanes may also be provided on long stretches of other roadway. On two-lane roads, passing in the lane of oncoming traffic is sometimes allowed given a long enough straightaway, if the broken line is on the normal side of travel.

A COLLECTOR LANE of a road is used for slower moving traffic and has more access to exits/off ramps.

A TRANSFER LANE of a road is used to move from express lanes to collector lanes, or vice-versa; it is somewhat similar to an auxiliary lane.

A MERGE LANE is a lane or onramp used to merge two flows of traffic into one, with the merge lane being the lane that disappears at the end of the merging area. Merge lane lengths depend mainly on the speed differential of the two merging flows, as the slower flow has to use the lane to accelerate.

THE EMERGENCY LANE of a road (also known as the breakdown lane, shoulder or hard shoulder) is reserved for breakdowns, and for emergency vehicles. The inner boundary of the lane often features rumble strips in order to physically warn drowsy or inattentive drivers that they are drifting off the roadway. This feature is seen especially often on highways and motorways, where the minimally-stimulating and monotonous nature of high-speed driving at night increases the chances for driver disorientation and serious injury or death if an accident does take place.

A DESIGNATED BICYCLE LANE is a portion of the roadway or shoulder designated for the exclusive or preferential use of bicyclists. This designation is indicated by special word and/or symbol markings on the pavement and "BIKE LANE" signs.

A BUS LANE is reserved for buses providing public transportation on a fixed route, sometimes with overhead catenary for trolleybuses. In some countries, bus lanes may also be used by some other traffic, such as taxis, bicycles and motorbikes.

A TRUCK LANE (United States) or crawler lane (Great Britain) is a lane provided on long and steep uphill stretches of high-speed roads to enhance the ability of vehicles which can maintain speed up the incline to pass those vehicles (usually heavy trucks) which cannot. In addition, these lanes are intended to optimize pavement performance and minimize pavement fatigue.

A REVERSIBLE LANE, which uses overhead lights, signs, poles or barriers to indicate the current direction of travel it is to be used for. Typically, it is used at rush hour to accommodate extra traffic, and at other times as a center turn lane. In between, there is approximately one hour where no traffic is allowed. While the idea is very simple, the term suicide lane became a common slang description for this design, because many people ignored their driving or the lights. Because of their history of numerous accidents and collisions, reversible lanes are rarely used now.

AN OPERATIONAL LANE OR AUXILIARY LANE is an extra lane on the entire length of highway between interchanges, giving drivers more time to merge in or out.

AN OVERTAKING LANE is the lane furthest from the shoulder of a multi-lane carriageway (sometimes called the fast lane, although this is deprecated by the authorities).

AN AVENUE[5] is a straight road with a line of trees or large shrubs running along each side, which is used, to emphasize the "coming to," or arrival at a landscape or architectural feature. In most cases, the trees planted in an avenue will be all of the same species, so as to give uniform appearance along the full length of the avenue. The French term, allée, is confined normally to avenues planted in parks and landscape gardens. In urban or suburban settings, "avenue" is often a qualifier for a road name, along with "lane", "street", "way", etc. In some cities which have a grid plan, such as Manhattan, there is a convention that avenues run in a north-south direction, while streets run in an east-west direction, or vice versa.

BULEVARD[6] has several generally accepted meanings. It was first introduced in the French in 1435 as boloard and has since been altered into boulevard; As a type of road, a boulevard is usually a wide, multi-lane arterial thoroughfare, divided with a median down the center, and roadways along each side as slow travel and parking lanes and for bicycle and pedestrian usage, often with an above-average quality of landscaping and scenery. Some people also use the term boulevard to refer to the division or central reservation in a road. It can consist of anything from a simple thick curb of concrete, to a wide strip of grass, to a thoroughly landscaped space of trees, shrubs, and other foliage; in urban areas, boulevards can also contain public art or memorials. Wide boulevards also sometimes serve as rights-of-way for trams or light rail systems. Another use for the term boulevard is for a strip of grass between a sidewalk and a road, and located above a curb. Though in Europe the two are often adjacent, many residential neighbourhoods in the United States and Canada feature strips of grass or other greenery between the sidewalk and the road, placed in order to both beautify the street and to provide a buffer between vehicles and pedestrians.

MAIN STREET[7] is the metonym for a generic street name of the primary retail street of a village, town, or small city in many parts of the world. It is usually a focal point for shops and retailers in the central business district, and is most often used in reference to retailing and socialising. Main Street is commonly used in the United States, Canada, and Ireland, some parts of Scotland and also in some countries in central Europe.

HIGH STREET is the common term in the United Kingdom.

In Jamaica as well as North East England and some sections of Canada, the usual term is FRONT STREET. In Cornwall, the equivalent is FORE STREET.

In some larger cities, there may be several Main Streets, each relating to a specific neighborhood or formerly separate city, rather than the city as a whole.

In Hong Kong, "Main Street" can be translated in Chinese into "ZHENG JIE" or "DA JIE"; however, in Hong Kong, officially "CENTRE STREET" is a branch road off Sheung Wan District.

In England, the terms "MARKET STREET" or "MARKET PLACE" are often used to designate the heart of a town or city, as is the more common High Street (certainly in newer urban developments, or towns or cities which were not original market towns).

HIGH STREET is often the name of a fairly busy street with small shops on either side, often in towns and villages.

In Sweden, almost all towns and cities have their own main street, a street called "STORGATAN" (Literally means, "THE BIG STREET"). They are typically surrounded by stores and restaurants, and in most cases open for pedestrians only, where no vehicles are allowed.

Likewise in Norway, this type of street is called "GÅGATE" (Literally means "WALKING STREET").

JALAN BESAR (roughly translated from Malay as "MAIN ROAD") is a common street name used in Malaysia when referring to main streets of older urban centres in the country. Such main streets were originally constructed during British colonisation, and were named in English as "Main Street" or "Main Road", depending on the size and nature of the urban centre.

In rural Sindh there are many small villages or sub districts or taluka level settlements that have one main central street bazaar (market) also known as “DHAK BAZAAR” (literally means a “COVERED MARKET”) which is an example of Main Street in our local context of Pakistan.

A SIDE STREET[8] is a street that intersects a main street and ends there. Most side streets are lined with residences. Side streets when built are mostly intended only for the traffic of their residents and visitors.

A TWO-WAY STREET[9] is a street that allows vehicles to travel in both directions. On most two-way streets, a line is painted down in the middle of the road to remind drivers to stay on their side of the road. If there is no line, a car must stay on the appropriate side and watch for cars coming in the opposite direction and prepare to pull over to let them pass. A two-way street can also be used as an idiomatic metaphor to indicate that something goes both ways. For example, "Communication within a relationship must be a two- way street that is heavily traveled in both directions."

A NUMBERED STREET[10] is a street whose name is a number rather than a worded name. Numbered streets, are commonly identified with names like "street," "avenue," etc., are among the most common street names found in North America. Numbered streets exist in cities which have grid-based naming systems, with numbers usually starting at 1 and then proceeding in numerical order. Some cities also have lettered street names. For example, Washington, D.C., has streets identified as a letter followed by "Street," such as Street A. New York has avenues titled "Avenue" followed by the respective letter of the alphabet, such as Avenue D.

A WALKWAY[11] is an umbrella term for all formal surfaces which support the act of walking. This includes sidewalks, trails, paths, stairs, ramps and open passageways. The walkway is a path for walking that is generally not enclosed. It can be at ground level, or it can be elevated, such as a boardwalk, or a floating dock/trail. It can be a simple constructed path or something more complex to cross a road or a body of water. An open pedestrian overpass or a special tunnel is also an element of a walkway. It can also be used to board and remove passengers from aircraft to the terminal building.

A CUL-DE-SAC[12] is a dead-end street with only one inlet/outlet. In urban planning culs-de-sac are created to limit through-traffic in residential areas. While some culs-de-sac provide no possible passage except in and out of their road entry, others allow cyclists, pedestrians or other non-automotive traffic to pass through connecting easements or paths. The word "cul-de-sac" and its variants, "dead end" and "no exit", have inspired metaphorical uses in literature and in culture too.

TRAFFIC CALMING[13] is a set of strategies used by urban planners and traffic engineers which aim to slow down or reduce traffic, thereby improving safety for pedestrians and bicyclists as well as improving the environment for residents. Traffic calming was traditionally justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic. However, streets have many social and recreational functions which are severely impaired by car traffic.

The Livable Streets study found that residents of streets with light traffic had, on average, three more friends and twice as many acquaintances as the people on streets with heavy traffic which was otherwise similar in dimensions, income, etc.

For much of the twentieth century, streets were designed by engineers who were charged only with ensuring traffic flow and not with fostering the other functions of streets.

The basis for traffic calming is broadening traffic engineering to include designing for these functions. There are 3 "Es" that traffic engineers refer to when discussing traffic calming: Engineering, (community) Education, and (police) Enforcement.

Because neighborhood traffic management studies have shown that often it is the residents themselves who are contributing to the perceived speeding problem within the neighborhood, it is stressed that the most effective traffic calming plans will entail all three components, and that engineering measures alone will not produce satisfactory results.

A number of visual changes to roads are being made, to many streets, to bring about more attentive driving, reduced speeds, reduced crashes, and greater tendency to yield to pedestrians.

Visual traffic calming includes lane narrowing (9-10'), road diets (reduction in lanes), use of trees next to streets, on-street parking, and buildings placed in urban fashion close to streets.

Physical devices include speed humps, speed cushions, and speed tables, sized for the desired speed. Such measures slow cars to between 10 and 25 miles (15-40 km) per hour. Most devices are made of asphalt or concrete but rubber traffic calming products are emerging as an effective alternative with several advantages.

TRAFFIC CALMING CAN INCLUDE THE FOLLOWING ENGINEERING MEASURES:
Narrower Traffic Lanes — streets can be narrowed by extending the sidewalk, adding bollards or planters, or adding a bike lane or parking. Narrowing traffic lanes differs from other road treatments by making slower speeds seem more natural to drivers and less of an artificial imposition, as opposed to most other treatments used that physically force lower speeds or restrict route choice.

Speed Bumps, sometimes split or offset in the middle to help emergency vehicles reduce delay.

Speed Humps, parabolic devices that are less aggressive than speed bumps and used on residential streets. Speed Tables, long flat-topped speed humps that slow cars more gradually than humps. Speed Cushions, a series of three small speed humps that slow cars down but allow emergency vehicles to straddle them so as not to slow response time. Chicanes, which create a horizontal deflection causing vehicles to slow as they would for a curve; Raised Pedestrian Crossings and Raised Intersection.

Curb Extensions (also called bull bouts) which narrow the width of the roadway at Pedestrian Crossings. Pedestrian Refuges or small islands in the middle of the street; Median DIVERTERS to prevent left turns or through movements into a residential area; Changing the surface material or texture (for example, the selective use of Brick or Cobblestone); Additional give way (yield) signs; Converting One-Way Streets into Two-Way Streets. Chokers, which are curb extensions that narrow the roadway to a single lane at points.

Allowing parking on one or both sides of a street, converting an intersection into a Cul-De-Sac or Dead End, Boom Barrier, restricting through traffic to authorised vehicles only. Close streets to create the Pedestrian Zones. Watchman traffic calming system etc.

ROAD CROSSING:
A pedestrian crossing[1] or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely with the flow of vehicular traffic. Pedestrian crossings are often at intersections, but may also be at other points on busy roads that would otherwise be perilous to attempt to cross. They are common near schools or in other areas where there are a large number of children. Crosswalks can be considered a traffic calming technique.

CHARACTERISTICS OF ROAD CROSSING:
Crossings are of various types. The simplest crossings may just consist of some markings on the road surface. These are often called Zebra crossings, referring to the alternate white and black stripes painted on the road surface. Depending on local laws, pedestrians crossing the road may or may not have priority over road traffic when using the crossing. If the pedestrian has priority, then they have an incentive to use the crossing instead of crossing the road at other places. In some countries, pedestrians may not have priority, but may be committing an offence if they cross the road elsewhere. In this respect term Jaywalking is used. Jaywalking[2] is an informal term used to refer to illegal or reckless pedestrian crossing of a roadway. Examples include a pedestrian crossing between intersections (outside a crosswalk, marked or unmarked) without yielding to drivers and starting to cross a crosswalk at a signalized intersection without waiting for a permissive indication to be displayed.

Some crossings have special signals consisting of electric lamps or light-emitting diode (LED) panels. The signals allow pedestrians and road traffic to use the crossing alternately. On some traffic signals, pressing a button is required to trigger the signal. These signals may be integrated into a regular traffic light arrangement or may be on their own if the crossing is not at an intersection. Audible or tactile signals may also be included to assist people who have poor sight. Sites with extremely high traffic or roads where pedestrians are not allowed (freeways or motorways) may instead be crossed pedestrian bridges or tunnels. A variation on the bridge concept, often called a skyway or skywalk, is sometimes implemented in regions that experience inclement weather. In many cities, countdown clocks are being added to give notice to both drivers and pedestrians the time remaining on the crossing signal. Special markings are often made on the road surface, both to direct pedestrians and to prevent motorists from stopping vehicles in the way of foot traffic.

There are many varieties of signal and marking layouts around the world and even within single countries. In the United States, there are many inconsistencies, although the variations are usually minor. There are several distinct types in the United Kingdom, each with their own name. Pedestrian refuges or small islands in the middle of a street may be added when a street is very wide, as these crossings can be too long for some individuals to cross in one cycle. In places where there is very high pedestrian traffic, pedestrian scrambles may be used, which stop vehicular traffic in all directions at the same time. Another relatively widespread variation is the Curb extension (also known as a bulb-out) which narrows the width of the street and is used in combination with crosswalk markings.

STREET LIGHT:
A Street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road, which is turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate automatically in dark weather. Also, it is not uncommon for street lights to be on posts which have wires strung between them, such as on telephone poles or utility poles.

HISTORY OF STREET LIGHTING[14]:
Before incandescent lamps, gas lighting was employed in cities. The earliest lamps required that a lamplighter tour the town at dusk, lighting each of the lamps, but later designs employed ignition devices that would automatically strike the flame when the gas supply was activated. The earliest of such street lamps were built in the Arab Empire, especially in Córdoba, Spain.[15]

The first electric street lighting employed arc lamps, initially the 'Electric candle', developed by the Russians in 1875. This was a carbon arc lamp employing alternating current, which ensured that the electrodes burnt down at the same rate.

Thames Embankment in London had the first electric street lighting in Britain.

The United States was swift in adopting arc lighting, and by 1890 over 130,000 were in operation in the US, commonly installed in exceptionally tall moonlight towers. The first street in the UK to be lit by electric light was Mosley Street, in Newcastle-upon-Tyne. The street was lit by Joseph Swan's incandescent lamp in February, 1879.[16]

First in the United States, and second overall, was the Public Square road system in Cleveland, Ohio, on April 29, 1879. Wabash, Indiana holds the title of being the third electrically-lit city in the world, which took place on February 2, 1880. Four 3,000 candlepower Brush arc lamps suspended over the courthouse rendered the town square "as light as midday."

Kimberley, a city in the centre of South Africa, was the first city in Africa to have electric street lights - first lit on 1 September 1882. In Latin America, San Jose, Costa Rica was the first city; the system was launched on August 9, 1884, with 25 lamps powered by a hydroelectric plant.

Timişoara, in present-day Romania, was the first city in mainland Europe to have electric public lighting on the 12 of November 1884. 731 lamps were used. In 1888 Tamworth, New South Wales, Australia became the first location in the Southern Hemisphere to have electric street lighting, giving the city the title of "First City of Light".

Arc lights had two major disadvantages. First, they emit an intense and harsh light which, although useful at industrial sites like dockyards, was discomforting in ordinary city streets. Second, they are maintenance-intensive, as carbon electrodes burn away swiftly. With the development of cheap, reliable and bright incandescent light bulbs at the end of the 19th century, they passed out of use for street lighting, but remained in industrial use longer.

Incandescent lamps were primarily used for street lighting until the advent of high-intensity discharge lamps. They were often operated in high-voltage series circuits. Series circuits were popular since the higher voltage in these circuits produced more light per watt consumed.

Furthermore, before the invention of photoelectric controls, a single switch or clock could regulate all the lights in an entire district. To avoid having the entire system go dark if a single lamp burned out, each street lamp had to be equipped with a device that ensured that the circuit would remain intact.

Early series street lights were equipped with isolation transformers that would allow current to pass across the transformer whether the bulb worked or not. Later the FILM CUTOUT was invented. The film cutout was a small disk of insulating film that separated two contacts connected to the two wires leading to the lamp. If the lamp failed (an open circuit), the current through the string became zero, causing the entire voltage of the circuit (thousands of volts) to be imposed across the insulating film, penetrating it as described in Ohm's law.

In this way, the failed lamp was bypassed and illumination restored to the rest of the street. (This is the same principle used in Christmas tree lights. The street light circuit contained an automatic device to regulate the voltage in the circuit, preventing the current from increasing as additional lamps burned out, preserving the life of the remaining lamps.

When the failed lamp was replaced, a new piece of film was installed, once again separating the contacts in the cutout. This style of street lighting was recognizable by the large porcelain insulator that separated the lamp and reflector from the light's mounting arm. The insulator was necessary because the two contacts in the lamp's base may have operated at several thousands of volts above ground/earth.

Today, street lighting commonly uses high-intensity discharge lamps, often HPS high pressure sodium lamps. Such lamps provide the greatest amount of photopic illumination for the least consumption of electricity. However when scotopic/photopic light calculations are used, it can be seen how inappropriate HPS lamps are for night lighting. White light sources have been shown to double driver peripheral vision and increase driver brake reaction time at least 25%. When S/P light calculations are used, HPS lamp performance needs to be reduced by a minimum value of 75%. This is now a standard design criterion for Australian roads.

PURPOSES OF STREET LIGHTS:
There are three distinct main uses of street lights, each requiring different types of lights and placement. Misuse of the different types of lights can make the situation worse by compromising visibility or safety.

BEACON LIGHTS
A modest steady light at the intersection of two roads is an aid to navigation because it helps a driver see the location of a side road as he comes closer to it and he can adjust his braking and know exactly where to turn if he intends to leave the main road or see if someone is at the intersection.

A beacon light's function is to say "here I am" and even a dim light provides enough contrast against the dark night to serve the purpose.

To prevent the dangers caused by a car driving through a pool of light, a beacon light must never shine onto the main road, and not brightly onto the side road. In residential areas, this is usually the only appropriate lighting, and it has the bonus side effect of providing spill lighting onto any sidewalk there for the benefit of pedestrians. On Interstate highways this purpose is commonly served by simply placing reflectors at the sides of the road to reflect the light coming from people's headlights.

ROADWAY LIGHTS:
Street lights are not normally intended to illuminate the driving route (headlights are preferred), but to reveal signs and hazards outside of the headlights' beam. Because of the dangers discussed above, roadway lights are properly used sparingly and only when a particular situation justifies increasing the risk. This usually involves an intersection with several turning movements and much signage, situations where drivers must take in much information quickly that is not in the headlights' beam.

In these situations (A freeway junction or exit ramp) the intersection may be lit so that drivers can quickly see all hazards, and a well designed plan will have gradually increasing lighting for approximately a quarter of a minute before the intersection and gradually decreasing lighting after it.

The main stretches of highways remain unlighted to preserve the driver's night vision and increase the visibility of oncoming headlights. If there is a sharp curve where headlights will not illuminate the road, a light on the outside of the curve is often justified. If it is desired to light a roadway (perhaps due to heavy and fast multilane traffic), to avoid the dangers of casual placement of street lights it should not be lit intermittently, as this requires repeated eye readjustment which implies eyestrain and temporary blindness when entering and leaving light pools.

In this case the system is designed to eliminate the need for headlights. This is usually achieved with bright lights placed on high poles at close regular intervals so that there is consistent light along the route. The lighting goes from curb to curb. Research a few years ago suggested that by comparison to other countries, more pedestrians are hit by motor vehicles at night in Britain.

The theory behind this was that Britain almost exclusively, used low pressure sodium street lighting, (LPS); unlike the rest of the world that use mercury vapour gas discharge lighting. This was most noticeable when flying in from Europe at night and seeing a warm orange glow when approaching Britain. LPS lighting, being monochromatic, shows pedestrians as shadowy forms, unlike other forms of street lighting. In recognition of this, pedestrian crossings are now lit by additional "white" lighting, and sodium lighting is being replaced by modern types.

SECURITY LIGHTING:
Security lighting is similar to high-intensity lighting on a busy major street, with no pools of light and dark, but with the lighted area extending onto people's property, at least to their front door. This requires a different type of fixture and lens. The increased glare experienced by drivers going through the area might be considered a trade-off for increased security. This is what would normally be used along sidewalks in dense areas of cities. Often unappreciated is that the light from a full moon is brighter than most security lighting.

DANGERS OF STREET LIGHTS:
There are two optical phenomena that need to be recognized in street light installations. The loss of night vision because of the accommodation reflex of drivers' eyes is the greatest danger. As drivers emerge from an unlighted area into a pool of light from a street light their pupils quickly constrict to adjust to the brighter light, but as they leave the pool of light the dilation of their pupils to adjust to the dimmer light is much slower, so they are driving with impaired vision. As a person gets older the eye's recovery speed gets slower, so driving time and distance under impaired vision increases. Oncoming headlights are more visible against a black background than a grey one. The contrast creates greater awareness of the oncoming vehicle. Stray voltage is also a concern in many cities. Stray voltage can accidentally electrify light poles and has the potential to injure or kill anyone who comes into contact with the pole.[17]

Some cities have employed the Electrified Cover Safeguard technology which sounds an alarm and flashes a light, to warn the public, when a pole becomes dangerously electrified. There are also physical dangers. Street light stanchions (poles) pose a collision risk to motorists. This can be reduced by designing them to break away when hit (frangible or collapsible supports), protecting them by guardrails, or both. High winds or accumulated metal fatigue also occasionally topple street lights.

[18] http://en.wikipedia.org/wiki/Pedestrian_crossing

[19] http://en.wikipedia.org/wiki/Jaywalking

TOWN PLANNING LECTURES BY RAVINDAR KUMAR

Wednesday, May 20, 2009

LAYOUT OF STREET, ROAD CROSSING AND LIGHTING

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