Engineering ra)onale

The design challenge is to create a varia1on of a road segment, of type EKL 3 which is cheap, eco friendly and safe for traffic. The two parameters which influence the embodiment are the curve angle and the road width. The economical high performance criteria is represented by the surface area of road segment which is needed to realize the project. The lower the area is, the less expensive is the construc1on as less material/work is needed. The ecological aspect is linked to the surface area as well, because the impact is higher on the nature as more area has to be reserved for the road and more ground is being sealed. Opportuni1es are less cost because of less expenses and lower emission through less produc1on of materials. The road has to be safe to use too. The criteria for that is the sight distance of the road. A long sight distance improves traffic safety by enabling to see oncoming traffic beHer and react earlier. Therefore a short viewing distance increases risk of an accident. Improvement in traffic safety reduces the material damages and human injuries etc. It has been recognized that the sight distance does profit form a narrow curve angle and a wide road. Although the width only has a small effect on the sight distance compared to the angle/shape. On the other hand the surface area got bigger as well, which is a nega1ve effect.

The model

To understand the rela1on of input on the performance criteria a parametric model has been programmed. As an input 3 points are established to create the central curve of the road. Two points are fixed and one can be changed in their x and y direc1on, which ranges from 20 to 50m in 0.1 steps. This affects the shape of the road. Another input is the road width. It design space ranges from 10 to 12m total as the “RAL” suggests in 0.1 steps.

The number slider of the curve is being used to create the central curve. The points are being managed in a list. The three points are used to create a NURBS curve which is the central line of the road segment.

Using that curve the surface has been created. Therefore a pane with a rectangle frame has been used to create a surface by SWEEP. The width of the rectangle can be changed and represents the width of the road. The surface is calculated to assess the performance. It’s an output.

The central strip is simply a long rectangle which is “layed down”. It’s centre are the points of the central curve.

The side strip is a curve which runs through the point translated form the central strip by the width of the road devided by two and offset by 0.5m as in the “RAL 2012” suggested.

As a performance indicator the sight distance is introduced. It is the distance form the edge of the right lane to the middle of the oncoming lane in the centre of the segment. It’s length is an output of the model.

For beHer understanding a method has been programmed, to see the curve angle, as the coordinates are not really useful. The angle of the curve includes the intersec1on of the rela1ve Z axis of the entry and exit of the segment.

Design space

The limit of the design model is that the road cant be straight. Only an angle of min 97 degrees can be explored. The maximum angle is 131 degrees. It is not included because it is a road segment of a curve, although a straight lane has maximum sight distance and therefore would improve performance of the design. On the other hand a straight shape would be more invasive in natural habitat or lacks flexibility with lakes etc.

Moreover the road cant be wider than 12m and narrower than 10m. Thus cross sec1ons with more or less lanes are not included in the design space. Therefore EKL1 with three lanes would provide more viewing distance and more safety as one lane is of overtaking.

Alterna)ves

Alterna1ve 1

The first alterna1ve priorizes maximum safety, which equals the highest viewing distance possible. This is achived through the lowest curve angle possible (98°) and the widest road configura1on. The road shape is stretched and wide with 12m width. This enables road users to see oncoming traffic at a distance of 34m. The wider cross sec1on adds safety by improving the view even more and gives more space for maneuvering. Although it is the most safe ist most likely to be the most expensive to build and has the most impact on nature, as it has the most are with 2019 qm. The design speed of this could be the highest as its the safest design.

Alterna1ve 2

Alterna1ve two embodies a mix of both. Specifically this means the average values of inputs. The road is neither steep nor stretched, or neither narrow or wide. The x and y is now 35m and it results in an angle of 109°. The sight distance is now 28.3m and the area is 1370qm. This configura1on is in rela1ve terms a balance without extremes. This will have moderate benefits for cost, impact on nature and safety/social.

Alterna1ve 3

The last alterna1ve priories ecological and therefore economical aspects. Its achieved through the smallest x/y input of 20 m. This results in a high angle of 131° and therefore reducing total area to 895qm and sight distance to 22m. Its quiet narrow with 10 m which affects economical and ecological aspects posi1vely like less area sealed and less material needed and therefore reduce emission of produc1on etc. The low impact and low cost can make this the best design alterna1ve overall. But in general is this the unsafest design. The design speed must be lower to prevent accidents. The view distance is only 22m compared to the other the lowest and therefore the unsafest.

Overview

This table shows a comparison of the design alterna1ves to highlight each scenarios strengths and weaknesses.