Sight: Distance analysis

- [Instructor] Sight distance analysis does exactly what it says on the tin. It helps to identify blind spots or sight failure zones which is just fancy way of saying there is something blocking your view and the road ahead. Before we get started, head over to sight distance analysis A bookmark number 9 and don't try to follow along here I just want to have a quick chat with you about what we actually see when we do sight distance analysis. So we have a component road here, you can see the stations along it and if we were to click from the revered modifier, road way design sight distance button, we have the sight distance panel.

Now there are a number of visual options that you've got here including sight zones, accident zones, sight envelopes, that's on the road and then from this sight pin which is where you put the little pin that works all of this out. You've got sight regions, you got sight lines and you have distance lines. So those are the things that we are going to look at. But before we go on let's just look at the analysis properties as well. So we have stopping sight distance, which is the minimum distance a vehicle driver needs in order to stop before colliding with something in front of him.

And passing sight distance which is the minimum sight distance required to allow a driver to overtake without smushing into something on the opposing lane. So those are the things we can look at with the sight distance analysis in InfraWorks. So let's get started. Let's hit escape to deselect our line and just head back to our bookmark number nine; sight distance analysis and we're going to look at this particular road over here.

As I mentioned before it has to be a component road and what I do is I usually right click and hide the geometry just because it makes it a little bit clearer to see. You may also want to look at, either using the conceptual view or the engineering view, it's up to you, depends on wat you think is clearer. But once you've done that, hit the sight distance button and the panel will come up.

So from the road analysis properties method, let's choose stopping sight distance, so how far ahead you need to be able to see in order to stop in time if a vehicle has broken down or has stopped suddenly. The next one is forward or backwards. So if you don't know which way your road is going, go back to the road geometry and check out the stations. So this station over here is 214, this one is 221.

So obviously, this way is forward. So coming towards the screen. So what are we going to choose, let's choose backwards and then also which lane you want. Now we don't have to do anything here because there is only one lane in each direction. However, if there is more than one lane, the lane closest to the center line will be lane one. So if we had two, say for example this component over here was a lane, that would be lane two.

So we don't have to worry about that right now, click road decorations because that will decide whether or not you have to take into account things like lamp posts or bus stops or bus shelters, that kind of thing, and then click analyze. So here we have the results. So in order to make it clearer while we talk through everything, I'm going to switch off the road visual options on the side road here.

So sight zones are these colored zones that I mentioned; so the yellow means that there is a sight failure. If you mark over the section of the road it will tell you where the sight failure is. The blue means that sight is clear. If we click on accident zones, you'll notice that in this blue area here, where the sight is clear, you still have an accident zone. So that is somewhere because of limited visibility further back in the lane you may have some accidents that happen in this area.

Then third, let's look at the sight envelopes. Now these show where we cannot see, there is an obstruction and blue is where we can see. Let's click place sight pin and you'll notice that a little pin is attached to the end of your cursor. Place that anywhere along your lane and this gives us, if we turn this off just to get some better visual clarity, this gives us the sight line and the distance line.

We'll switch those off and have a look at them one at a time. So the sight region is where you can see from that particular point. Sight line is where you want to see in order to stop properly. And then the distance line as well, the distance is this thick back line over here that you can see and imagine you're standing at this point in the pin. This thick white line over here points to the hypothetical eye level to the desired sight distance.

So that's how far you need to see in order to stop properly and in time. So let's have a look at other things that may affect our analysis. I'm going to change the design speed of this road, we have a design speed of 45 kilometers and hour, I'm going to change it to 60 kilometers an hour. And you'll notice that our sight distance analysis has been wiped clean, that is because it's very dependent on how quickly a vehicle would be going on this road.

So we're going to do the exact same thing, stopping sight distance, we're going backwards, we don't have to change the lane, hit analyze again and then just have a look at how differently, switch all the visual options on, have a look at how much more different this particular road looks now. We have far more obstructed sight zones, the accident zones are far more prevalent and we have far more sight failure zones as well.

That's because obviously when you're traveling at 60 kilometers an hour as opposed to 45 kilometers an hour, you need that much more distance in order to stop before running into the back of the truck in front of you. So that is sight distance analysis on roads. Let's have a look at sight distance analysis on intersections.