Road junction and Design Principles,Types of Junctions

Design Principles,Types of Junctions

Here you can get Road junction, Design Principles and Types of Junctions.

A junction is defined because the general area where two or more roads join or cross. The importance of design of a junction stems from the very fact that efficiency of operation, safety, speed, cost of operation and capacity are directly governed by the design.

In the design of a junction, the needs of all road users including pedestrians, cyclists and commercial vehicles should be considered. Also, constraints concerning driver behavior, traffic and geometry got to be taken under consideration within the design of a junction.

Extra risks face motorists wherever roads meet and diverge, whether at crossroads, T-junctions, roundabouts or forks, but by using the techniques of advanced driving and applying a systematic approach, junctions are often addressed as safely as the other part of the road system. Accidents don’t ‘just happen’ of their own accord — they’re caused by bad driving. While you ought to always take extra care at junctions, you want to recognise that they present a perfect opportunity for other road users to cause trouble. we’ve all seen other drivers adopt their own odd ways of approaching junctions and navigating their way through them. get on your guard, therefore, for what a road safety expert might describe as ‘an accident waiting to happen.


The most opportunities for error, whether on your part or another road user’s, occur at crossroads. once you are approaching on the minor route, or when neither route has precedence, plan ahead and be prepared to prevent even though the signs may tell you simply to offer way. If your side of the road is wide enough for 2 lanes of traffic, make sure that you begin moving into the right one at an early stage after first checking your mirror and signalling accordingly.

Stay within the left-hand lane if you plan to go straight across unless lane markings tell you to try to to otherwise, since keeping within the right-hand lane can dangerously mislead other motorists; besides, the right-hand lane at many crossroads is arranged in order that travelling straight on inconveniences or even endangers other road users as you fit back to one line of traffic. even if there’s insufficient room for doubling up the traffic lanes, it’s still better to edge over to the side corresponding with the route you’ll follow as you allow the junction.

Straight ahead or turning left

When planning to go straight ahead or turning left, the procedure is relatively simple: wait until the road is obvious to right and left, make sure nothing is approaching from the other minor road and accelerate smartly away. Always watch, however, for one common explanation for accidents. An oncoming vehicle signalling to show left will lead you to expect it to show off at the crossroads and not interfere together with your intended path, but indicators are often left on by mistake. the driving force could also be getting to go straight ahead without realising that he’s telling other road users otherwise. Never assume that a vehicle will turn until you really see the driving force begin getting into another road. If you pull call at front of him and cause a collision, the law would be unlikely to favour you.

Try to keep impatience in check once you try to show left and traffic is heavy. a niche might look large enough for you to slide into if you accelerate hard enough and therefore the driver behind slows down, but don’t roll in the hay . aside from being dangerous when the margins are slender, this type of driving is discourteous. An accident could happen if the opposite driver is slow to react, if your engine falters or if you merely misjudge your move. this is often a quite unnecessary risk only for the sake of shaving a couple of seconds off your journey time. Everyone knows the saying: it’s better to be a couple of minutes late during this world than a couple of years early within the next.

Turning right

Right turns at crossroads are often more complicated, although they’re governed by an equivalent rules about not pushing in or taking indicator signals for granted. There are often confusion if opposing traffic is additionally turning right as drivers decide whether to pass offside-to-offside or the other way around . half the country’s drivers seem to favour a method , the other half the other. However, there’s just one safe rule, which is to pass offside-to-offside; in other words, pass behind an opposing vehicle waiting to show right. Do otherwise only road markings or the junction layout dictate it.

Some drivers seem to object to the present procedure because it can limit the number of vehicles ready to get through a right turn in one traffic light sequence, also as requiring a niche to be left in an opposing line of vehicles waiting to show right, but it’s much safer. It means each driver features a clearer view down the road ahead as he makes his turn. The nearsideto-nearside approach, where vehicles turn across the bows of the opposing line of traffic, forces each driver to sniff out blindly across the traffic stream, greatly increasing the probabilities of an accident. it’s hardly surprising that numerous collisions happen when a driver is popping right.

Courtesy at the crossroads

Using the more major of the two routes at a crossroads does not entitle you to drive as you like. Show courtesy and consideration to other road users, but not so excessively that you put politeness before practicality. By all means let someone out of a side turning if it is safe for you to do so, but it is dangerous and disruptive of traffic flow if you have to cause other drivers behind to brake. Misplaced courtesy can cause accidents if drivers around you are not expecting it. Let someone trying to pull out of a side road wait a little longer if you are in any doubt.

Traffic lights

Never cash in of traffic light changes to undertake to nip through a junction and save yourself time. An alarming number of accidents in our towns and cities are caused by drivers trying rashly to save lots of a couple of seconds, and therefore the victims are often pedestrians. you ought to stop if you’ll reasonably do so when green changes to amber, and you want to certainly never undergo the lights after amber has changed to red. Nor you’ve got to|must you”> do you have to anticipate the change to green by moving away on red and amber; by all means keep an eye fixed on the lights controlling the routes crossing your path in order that you have advance warning of when your lights are to vary , but don’t use this to require liberties with the lights.

Since local authorities don’t usually give much warning of filter lights ahead, sooner or afterward an unfamiliar road you’ll probably end up sitting at a green left-turn filter once you want to travel straight on. Even a quick pause will probably bring the sound of horns from behind. you’ll sit there expecting the all-green phase, but it’s far less selfish to form the turn and find an alternate way of getting back on to your route.


The rules outlined for procedure at crossroads apply equally to T-junctions: do not muscle your way into traffic flow on the idea that other drivers will slow down for you, and always be aware that the vehicle with its indicator flashing might not make the end up of your path which you expect it to.

Many T-junctions have a mini slip-road in order that you’ll merge more easily with the traffic flowing on the most road. actually they’re often designed only to avoid a slow-speed 90-degree activate to a busy highway , and usually don’t offer sufficient width or length to permit you to succeed in the speed of the most traffic flow before you slot in. Treat these slip-roads with care: hold back if you’ve got any doubts and await a suitable break within the traffic. All the same, don’t be too timid at those slip-roads which are wide and long enough to figure well. Use them as they’re intended to be used, sort of a motorway slip-road. If you are doing encounter an over-cautious driver who has stopped at the top of the slip-road expecting an opportunity within the traffic, accelerate smartly and move out into the most road early, as long as it’s safe to try to to so, so as to be within the main stream before you pass the stationary vehicle.


How to tackle a roundabout

Hanging back at roundabouts are often even as unnecessary. you ought to strike the proper balance between reserve and haste by making a decisive, safe entry into the traffic flow. Large roundabouts carry fast-moving traffic but often provide enough width for you to maneuver into the nearside lane and build up your speed to match the flow of traffic around you. Small roundabouts have less acceleration space, but you would like less room because traffic moves more slowly. Roundabouts are designed for max flow and easy entry at junctions where traffic is heavy, so don’t queue unthinkingly at the approach roads. When traffic is light enough, it should be possible to enter a roundabout where visibility is sweet only with an inexpensive reduction in speed and a change to a lower gear, all the time checking as you run up to the entry point that no vehicles are coming from the proper. Where walls or hedges obscure visibility it’s going to be necessary to hamper almost to a stop. Except where the priorities are marked differently, traffic on a roundabout has right of way.

Priority is usually given to a major route passing through a roundabout, in order that drivers already on the roundabout need to subside once they meet this route. Changed priority is formed to assist speed traffic flow, except for a driver unfamiliar with the world the necessity to offer thanks to traffic entering the roundabout can cause a moment’s confusion. The advanced driver’s observation skills should alert him well ahead to an unusual circumstance like this, but the danger are often reduced by keeping in your correct lane and remembering signalling procedures in order that drivers around you’re conscious of your intentions.

How to negotiate a mini-roundabout

Mini-roundabouts , especially those where there’s a decent complex of two or three, can cause temporary confusion once you first meet unfamiliar ones, but the additional caution they require is sometimes regarded as their benefit. Since so many drivers are unsure of the procedure on them, traffic is slowed down to a safer speed. Except within the rare instances where road markings indicate differently, treat complexes of mini-roundabouts a bit like the other roundabout by giving thanks to vehicles coming from your right. Where a mini-roundabout is marked just by white lines on the road, never succumb to the temptation to chop across the island, albeit there’s no traffic about.

On all normal roundabouts you ought to keep to the established procedure outlined within the Highway Code unless lane markings tell you to try to to differently. If you propose to require the primary exit, you ought to keep to the left and signal a left activate your approach, keeping the indicator going until you allow the roundabout. If you propose to travel more or less straight across, still keep to the left on your approach and thru the roundabout, signalling a left turn after you’ve got passed the exit before the one you plan to require . Your anticipation as a complicated driver should have given you many time to maneuver into the left lane on your approach to the roundabout, but in very heavy traffic you might be obliged to remain over to the right; if this is often the case, hold your course until you would like to signal left and give way for your exit, taking care to not cut ahead of the other vehicles. For exits quite 180 degrees around the roundabout, take the right-hand lane on your approach and signal a right turn before you enter the roundabout. Keep the indicator going until you pass the exit before the one you want, at which point starting signalling left and give way for your exit.

Principles for Good Design of a Junction

  • The number of junctions should be kept a minimum.
  • The geometric layout should be so selected that hazardous movements by drivers are eliminated. this will be achieved by channelizing and staggering.
  • The layout of the junction should be easily understandable. this will be achieved by an honest layout, traffic islands, signs and road markings. Good visibility improves safety.
  • The amount of conflict points should be minimised by separating diverging and merging movements.
  • For poorly maintained vehicles, with lower braking and acceleration capability, a ‘dilemma’ zone may occur at signalized junction at the end of green stage, because the driver is unable to prevent in time or accelerate beyond the junction. Here a extended inter-green should be considered.
  • Speed change lanes (acceleration/deceleration lanes) are used on high speed, high volume roads from accident and delay consideration. they ought to be of sufficient width and length to enable a driver to maneuver vehicle onto it and reduce or raise speed to that of the turning or ‘thru’ traffic stream.
  • For right turn from the main road, offside diverging lanes should be used either by providing raised medians or ghost island.
  • On toll road roads, it’s beneficial to consider widening of the median, not only to include any offside diverging lane on the main road, but also to supply a shelter for right for right turning vehicles from the minor road, in order that the gap acceptance decision is split into two easier stages.
  • Corner islands are provided to offer turning guidance to diver and are often utilized in conjunction with speed change lanes. If corner lane area > 4.5 sq.m, then the island should be raised. Avoid large corner islands delineated only by pavement markings. Corner islands assist pedestrians in crossing wide areas of pavement at busy junctions.
  • On curve the rear wheels of vehicles track inside the front ones. One open highways curves the effect is a smaller amount pronounced and for a 3.65m lane width, pavement widening is merely required on curve of R < 150m.
  • A design vehicle should be chosen (e.g. a 15.5m articulated vehicle within the UK) and its track width on different turning radii and lock (steering angle) determined. In residential areas, the hearth tender or garbage pickup vehicles might be used as a design vehicle for this purpose. Computer programs, like AutoTrack etc. are available to simulate turning vehicles at intersection.

Types of Grade Separated Junctions

Diamond Type Junction

Simplest form of GSJ; minimised land take; simple slip road design; minimised cost due to single bridge; disadvantage is that all four quadrants are used to provide turning movement, which for different sites especially in urban areas may create several environmental problems.

Half Clover Leaf (Compact GSJ) Junction

It is used at similar flow levels to a diamond, particularly where site conditions are difficult, and the use of all full quadrants is not possible.

Dumb Bell Type Junction

Reduced cost due to single bridge and less land take; increased junction capacity and reduced land take compared with diamond; signalised gyratories could be considered.

Bridge Roundabout Junction

Too large; high circulating speed; leads to difficulties for the joining traffic


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