Lecture 52: Intersection Layouts - 10

[Music] [Music] let us now try to calculate our discussion on the intersection layouts in this particular lecture in the previous interaction we talked about the warrants which are there for providing the interchanges we also looked at the feasible combinations where the interchanges needs to be provided if different type of roads crosses each other then we talked about the geometric features and the ramp terminals wherein the entrance and the exit ram terminals were discussed now in this lecture we are going to talk about the weaving sections the ramp metering lane balancing and then there are certain suggestive layouts which can be there for ramps and wherein it takes care of the different type of movements with respect to the roadside activities or the traffic movements on the main highway so let us start with the weaving sections now waving sections means what first of all we have to understand that what type of weaving movement is going to be there weaving movement is like you are moving in a certain direction and then you have to make a change so you started making a change and then comes into this form but at the same time there is another vehicle which is going and it can keep going either straight or it can also deviate to increase the speed and then comes on the say the median lane and so this type of things all of these type of movements which are happening wherein the streams are involved so these actions are basically the weaving movement and this section is going to be the waving section so we have to take care of these type of movements when you are talking about the any turnings which happens and if there is a no lane discipline being followed by the drivers then it becomes quite difficult to control because you may find that the people from the right hand side are taking a left hand turn ah in ahead of a vehicle which is in the adjacent lane on the left so ah if those type of things are happening then that is becoming very hazardous situation but this is what we need to talk about because in the case of interchanges also these actions are going to be there and then ah these needs to be controlled so we have to see that how it can be controlled what are the lands which needs to be provided is what we are talking there so here what you can see is the maximum length over which the merging and diverging movements are defined this is usually 450 meters but when we look at this then it talks in terms of two aspects one is an influence area another is a traffic density so influence area of a waving section that is defined by the traffic density but when we talk about the traffic density then it is considering all the lanes which are there across which the vehicles are moving so it takes the average of all vehicles across all the lanes of the segment between the entry and exit points of the segment so whatever number of lanes are there whatever total traffic is there on the basis of that we can get the average value out of it now when we are looking at the influence area then it is reflected by the density of what lane the density of right and next to right lane and by the acceleration in the acceleration lanes 450 meter upstream of the diverse lane or downstream of the merge lane so this is the amount of area which we are going to consider basically the length which we are going to going to consider so we are going in this form and and similarly we are coming in this so whatever the acceleration and the acceleration lanes so ah from here we are going 450 meters and see from here we are going 450 meters so this is the total one this particular stretch which is going to be considered for this type of analysis now here what you can see is that there is a merging movement so the traffic is coming from here and there is a traffic which is moving on a through lane so they are merging at this point similarly there is a divergence so here the traffic is getting diverted on a ramp and there is a traffic which keeps going straight so there are possibilities so here another thing which is happening is that the traffic is merging from here and it then keeps going in this direction or it may get into the through lane like this but there is another traffic which is coming from this direction and wants to go straight and gets to the ramp which is there so it is exiting now so when this is happening then this is a big area in which the viewing actions or movements are going to be there of different vehicles so ah that is a another issue which will be there in this case so when we talk about this waving section then the lens needs to be looked at and these lengths have been defined here they are in kilometers so it is like point five kilometers say to ah something like as high as roughly three kilometers and they have been defined for different speed values and they are also being correlated with the entry flows which are in pcu per r per lane so you have the values of these entry flows they have been categorized and then they are also being talked in terms of the lane configurations so the lane configurations have been defined here so when we are talking about these lane configurations so it is related with like what the type of weaving sections or what type of merging or diverging sections with respect to the through sections are there so when we see here what we found is that when you are talking about say the three three six case here in this particular case the lower values of the traffic it is coming even less than point five kilometers but when you talk about the higher flows then it is roughly around 1.7 kilometers but when we have higher flows in a this type of a segmented condition that is 3 3 3 then the values are going to increase to a lot if we are talking about 70 kilometers per hour as a speed now another thing which needs to be ah considered is a ramp metering now ramp metering is that you are on a highway and say ah there is a cross road so a cross road is being provided and these two roads are crossing each other at different levels and say we are talking about this type of a connectivity where the traffic goes out so you are at an elevated system here and now you are merging at grade so when this traffic gets here there is a two opportunities one it goes left another one is it can take a turn to right and then moves on this one so this is one way of doing it so another way of understanding it is that you are coming in this form and that so the traffic is coming from a ramp and that goes on the acceleration lane and then goes ah into the main stream so the traffic is already there which is quite high on this direction so you need to control this particular traffic so all of these cases when you are trying to consider they can be done by way of the use of a traffic signals which are placed at these particular locations and that is what is being defined as a ramp meters so when these have been defined and when these have been placed in this way then what it helps is it helps in controlling the traffic which is moving on the segments ahead and the traffic always remains with the value less than the capacity of that particular segment so that is how the smooth flows or the continuous flows can be maintained so ah this is what is being talked ah in the other two lines as you can read also there now depending on the number of lanes and the uses of high occupancy vehicles so there can be two different categories of vehicle single occupancy and high occupancy vehicles so when we are having these different vehicles and that what number of lanes are there on the ramp on the basis of that this categorization is there what it says the ramp for single occupancy vehicles if it is a single lane ramp meter then for a peak our design volume is less than 720 vehicles per hour in this case or the and or the provision of high occupancy vehicle lane is not feasible so we are going to provide a ramp only for sov so these two things one is the design our volume is to be looked at another is the feasibility of a hov is to be looked at so based on that it is going to define now another case is that still here that the peak r design volume is up to 720 vehicles per hour but if the hov is equals to or more than 9 percent of the total peak or volume then an hov lane has to be added and that is where we are going to have a dual lane ramp meter which is there for sov and hov then rams for two sov is another case that is two single occupancy vehicles so dwell in ramp meter is provided in this case the peak r traffic is going to be more than 720 vehicles per hour so higher traffic values are there then even for a single occupancy vehicles more lanes are going to be provided now when we are providing these number of lanes on main highway and we are also providing the lanes on the ramps then there is a some amount of balancing is being done and that is what is being defined as lane balancing now this lane balancing is done so as to how a continuous smooth efficient movement of the traffic and that has to be ensured with respect to the merging or diverging sections with respect to the upstream or downstream of those merging and diverging sections now when we are looking at this then what number of lanes needs to be provided one thing we have already discussed when we talked about the rams is that it is going to be dependent on the total amount of traffic which is there and with respect to that we are going also going to look at the handling capacity of a lane and that will define whether we need to have two lanes or three lanes or more than that so this way you are going to have the basic numbers of lanes which needs to be provided now once this basic or the minimum numbers have been defined or decided then we are going to look at that what are the other things which are happening on that main highway how the traffic is being controlled on the main section or the carriageway for a through traffic which is moving in a certain direction so here what we have to look at that these needs to be maintained throughout the length of the highway and shall not be kept changing between the pair of interchanges otherwise the continuity is going to be lost now what is the guiding principle how to find out what should be the number of lanes under what conditions is what we are looking for the two cases one is entrance another one is exit entrance means you are coming from a ramp and you are getting into the main highway so that is what we are talking so the number of lanes beyond merging of two traffic streams so the traffic is here it is merging then this traffic is here this is there this can also be like this so we are talking about the number of lanes beyond merging so this is a merging area beyond that what number of lanes are going to be provided here that should not be less than the sum of all traffic lanes on the merging roadways minus one so whatever are the total numbers which are going to be there in this say if we have the ramp which is being provided with two lanes and it is a six lane divided system so there are three lanes so three plus two is what we are saying and minus one that means three plus two five so five minus one so four are going to be there so if this is three this is two then this is four or it can be maximum as some of all traffic lanes on the major roadway so it can also be five in this case similarly when you look at the exit conditions what it says is the number of diverging lanes on the main carriageway so you have diverted and on the main carriageway what are the number of diverging lanes are going to be there so this is number of lanes on the main carriageway after exit plus number of lanes on the exit ramp so the traffic is going this way and then this traffic is taking a turn so you have an exit ramp here and this is a through traffic on a highway so this is what we are like number of lanes on the main carriageway is this number of lanes on the exit ramps is this so we take the sum of these minus one is what the number of diverging lanes on the main carriageway so this is what is going to be defined so if again this is two lanes and this is two lanes so this is two plus two minus one so that means here it can be three lanes which is now being convert into two plus two another point what it says is that there can be certain exceptions and these exceptions are like for clover leaf loop ramp exits and it follows a loop ramp entrance and exits between the closely spaced interchanges in those cases there may be some issues and there the adjustments needs to be made in that now what type of adjustments can be this says the auxiliary lane may be dropped in a single lane exit and the number of lanes on the approach roadway can be number of through lanes beyond the exit plus the lane on the exit so beyond exit whatever number of lanes are there plus the one lane on the exit and that is how the total values are going to be there on the approach road so whatever is this approach road is there so this is what we are saying and then there is an exit on this direction so accordingly we are considering the travel way on the main carriageway should not be reduced by more than one lane at a time so this is also one another guiding principle so here you can see that here there is a case of a merging lane balance so what we see is that it is a main highway has two lanes and this merging ramp has one lane so total lanes are two plus one three minus one that is two so that is our three plus one four minus one three five minus one four and the same way it is being done so in other cases the another ah point which was said that it can be at the maximum equals to the sum of those lanes so it is two plus one so that is three three plus one that is four so these are the two criteria which have been there now when we talk about the diverging lanes so we said that how many lanes should be there on this diverging main carriageway was decided on the basis of the ah this diverging point and beyond that diverging point how many number of lanes are there on the through as well as the ramp based on that the sum of this minus one was the criteria so accordingly the values have been calculated so this is how we can see that what values needs to be provided at what location now when you are looking at these interchanges one another thing which needs to be taken care of is that their efficiency has to be looked at and this efficiency is in terms of the accessibility to the system that when how you can reach there ah how you can approach in terms of entrances or exits the mobility being ensured what type of quality of services being provided how reliable the services as well as how much safety has been ensured so these can be the parameters which can be used to examine and evaluate the effectiveness of any interchange now let us look at some of the suggestive layouts now here what you can see is that the traffic is there so there is a carriageway on which the traffic is moving and this is a median there is a service road so this is a bi-directional traffic on this road so this traffic can go this way and then it comes here when it comes here and it is going to move this is a parallel section and then finally it will come on this road so there is going to be a merging so when this is happening there is a metering being done here the traffic can be stopped here to see that if there is a lot of traffic moving on this then this may not be allowed and once there is an opportunity then the traffic can be allowed to move on this ah highway and can merge on that or there is another way is that this traffic because we are talking about a two directional condition here so the u turn is also being allowed in this form and these parts which are there they are five point five meters wide now this is another case where again you have a service road on this side at the same time there is a service load on the other side too and this merging action is going here so there is an acceleration lane and then the merging is happening so the traffic which is coming from here that is allowed to get into it but when it is getting allowed here it is being controlled similarly the traffic which is coming from this direction can get into this way because it has to merge into the main highway so again this is being controlled here and then they have been released and they get into the main highway so this is another type of a design where the service road is being continuously provided along the main highway here also there is a service road on this side and the service road on the other side but this can be the deceleration on this week and when it is coming from say this and it has gone into this direction so the traffic is going out of a system it can go to this service lane or this traffic which is coming from here can also take a u turn and go into this form so this is another design here what you found is that there is a service road here and there is a service road on this site too and then we are trying to see that how the traffic is getting in and out here so here the traffic is going out from the main highway moving in the parallel section then it takes a turn because it has to go in this direction or it can go straight so as to go in the right hand direction so both opportunities have been provided at this location but when it is getting merged in the other traffic then it is being controlled so as to see that the capacity or the smooth flow ahead or the downstream of this location has been maintained here this is a 90 degree sort of a condition where the traffic is moving in these directions there is a traffic which is coming from this service road and here it is a two directional traffic so the traffic can go in this can go straight and can take a left turn but if this has to get out and come into a highway so this is the way it can be done so it will come here and get merged or there is a traffic which is going out so it can go straight like this or it can move here and then get into the system so all of those movements which can be possible they have been taken care of when we are looking at this type of a design here now it is a combination of whatever the previous designs we have seen so here what you can see is there is a deacceleration here what you found is acceleration so here this is acceleration this is ah deceleration is there and we have the service roads being provided continuously and there is a another case where cross road is crossing this main highway as an underpass so it is going from below that so this is the another type of facility which can be there this again ah though we have the service road which is continuously moving with the highway and there is a crossover at this location so that has been taken care of so the traffic which comes from here so gets out of this or the traffic if it is coming it can be out so this is how the traffic can move in and out or there is a possibility of this traffic cutting in and out here also so all of those things now if you have to do then you have to see that how these things can be ensured similarly here there is a main highway which is elevated so there is a underpass at this location so what you found is this is a paved area and this is a paved area and beyond that we have the service road or the slip lane on all the sides so this is service road or the slip lane being provided there is a crossroads from where the traffic is coming so channelization is being done and the traffic which is moving here can move in this direction or it can move in any of such directions so these are being provided along with that whatever this area is being shown that is a pedestrian path if you remember we have seen these ah things previously too here what we can see is that there is a traffic which is moving on this main highway then it diverts it starts deaccelerating but the issue here is that it is getting a one ramp here and then it goes straight and gets an another ramp on this side so this close proximity of these two rams from each other make create some issue at this particular point where a weaving may happen ah of a vehicle which desires to be here and is wrongly being placed and that's where it just deviates to the other side so this merging and diverging is going to happen in these areas here again what you can see is that there is this ramp also is bringing traffic and the other ramp also is bringing traffic so there is going to be a lot of traffic in this area and this needs to be controlled either it should have been controlled by way of the ramp metering at the start but if it is not being done then these two traffic when they get into the system and then this try to get into the main highway system so this is going to be too much of congested so it would have been better if these two approaches which have been provided here they have been separated out or segregated out by each other here what we found is that there is a nose which is being provided here there is a median and the gap in the medium is being provided there is a ramp from where the traffic is coming and this traffic can move ah in this form or it can go into this direction and get into the other side of it so there is going to be a sort of a weaving action which is happening here so this needs to be properly designed so we have to increase the this merging diverging section or the weaving length which can go up to a length of say 450 meters and the sections which can go on the basis of the speeds to some kilometers to thats what we have discussed previously is what needs to be taken care of now in this particular one what you can see is there is a clover leaf arrangement where there are certain permanent structures which are being observed and because these permanent structures they cannot be acquired they cannot be removed so what needs to be done is that the design of the these clover leaf has to be adjusted what you found is that in this case it is a good loop but here this is a restricted loop so here probably there is no issue but here there is an issue so this has got a more straighter rather than in a loop condition the similar thing is happening at this point also this is one thing another thing is that because of the land constraints whatever area is available these two structures they are coming very close to each other so in this particular one it was observed that they were roughly around 1 or 1.5 or 2 meters away from each other which was not a right design that needs to be a bit farther away ok so there was an issue of the restricted speed and associated with that there was an issue of the radius of curve and spacing of ah structures and when we say stress new structure this is with respect to ramps so they have been taken care of and then only with respect to the given topography with respect to the given structures which were there as the physical features the design has been done so this is another case where you found that the roundabout is being provided and that route about the textured surfaces are being used and these texture surfaces defines the paths for the known motorized vehicles or the other way of doing it is that it is being provided in terms of a grade separated condition where the traffic is moving at different levels as well as there are spaces being provided for the pedestrians to cross this area at great separated condition say in terms of a subway or so on so this is also an important aspect when ah you have to take care of such intersections in an urban area which is quite busy so with this we come to the close of this module and now we are going to shift to the next module which is design of facilities we will start our interaction from the next lecture onwards till then thank you and bye [Music] hey [Music] you