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Design Time Costing

Updated October 19, 2017

This article applies to:
  • RoadEng Civil
  • RoadEng Forestry
  • Softree Optimal

In addition to being a very useful function for road design, cost calculation is a prerequisite to alignment optimization; the optimizer minimizes the cost. In this example, we will use design time costing with a hand-designed road alignment.

Alignment Properties Panel

First let’s look at the Alignment Properties Panel.

  1. Open the Softree Optimal application.
  1. File button | Open. Select Hart Rd.dsnx. Press Open.
  2. Arrange your screen to look like the figure below. You may need to
  3. arrange your visible windows by selecting the View tab | Tile Vertically

Figure 1: Softree Optimal with Alignment Properties Panel

The Alignment properties panel was created to do the following:

  • Manage multiple vertical alignments.
  • Define parameters required for design time costing and vertical alignment optimization.
  • Report cost and other information related to design time costing and vertical alignment optimization.

Alignment(s) Tree

The top part of the panel is a list of vertical alignments; for this example, there is only one alignment called V-Align 1: Hand Design.

  1. Click the button next to the alignment name to open the tree (as shown in the figure below).

Figure 1: Alignment tree control

The tree control displays parameters that are used for cost calculations and alignment optimization. The parameters relating to cost calculations are briefly outlined below.

  • Costs include the unit costs for cut, fill and haul.
  • Pits can be used to borrow and waste materials.
  • Sidecast is used to waste material alongside the road.

Information Area

The bottom part of the panel is the reporting area. It displays information about the selected alignment such as volumes and costs.

The contents and order of this list is configurable. Right click and Choose fields to report or press the button at the bottom of the panel.

The size of the information area can be changed. Click on the top of the information area to activate a slider to re-size the panel.

Figure 2: Reporting area

Cost Reporting

Now let’s use the Design Time Costing features.

  1. Press the Re-Cost^ button in the middle of the Alignment panel to open the dialogue box below.

Figure 3: Re-Cost Dialogue

  1. Press the Calculate button inside the dialogue box to begin the calculation.

The next steps will demonstrate the change in cost when the vertical and horizontal alignments are moved.

Note: It is assumed the reader is familiar with interactive design using RoadEng®; however, even if you haven’t used RoadEng® before, you can probably follow along by reading the detailed instruction steps (a, b, c, …).

  1. In the Profile Window, change the vertical alignment slightly:
    1. Right click and change to the Add/Edit IP tool (or select Home | Tool Selection | Add/Edit IP).
    2. Move your mouse over a VIP(indicated by the magenta square box symbol); note that the mouse cursor changes to a box .
    3. Click the mouse to capture the IP.
    4. Move the point slightly and left click to re-anchor the point.

Note: The information list is displayed grey after design modifications cause the costs and other items to be out of date.

  1. Re-Cost^ the alignment as before.

Note that the costs are different. Now to streamline this procedure:

  1. Press the Re-Cost^ button to re-open the dialogue box; this time, set the Auto checkbox; before pressing the Calculate button.

Now your design will automatically re-calculate the cost any time it is changed. This is only sensible for short alignments where re-cost doesn’t take too long.

  1. In the Plan window, capture and move an IP slightly and observe the updated cost.
    1. Move your mouse over an IP (indicated by the red square box symbol); note that the mouse cursor changes to a box .
    2. Click the mouse to capture the IP.
    3. Move the point slightly and left click to re-anchor the point.

Figure 4: Design Time Cost Reporting

Note: If Auto is checked, the cost will automatically update each time the alignment is changed. In some situations, this will noticeably slow recalculation.

Cost Parameters

The earthwork cost values reported in the steps above are dependent on the volumes and types of materials excavated and embanked. Softree Optimal allows you to specify what material layers are found in the ground and what materials you are using for subgrade fill. To calculate costs, you also need to provide cut/fill cost for each material and generic haul cost information.

Note: This document uses $ for currency. You can change the currency symbol by selecting menu Setup tab and choosing the Units tab.

  1. Click on the Options button and then click on the Unit Costs tab.

The Ground Types dialogue box will appear as shown in the figure below.

Figure 5: Cost Parameters

Handling Costs The Excavation and Embankment (Cut/Fill) costs are dependent on material type. Unit costs are entered in $ per Cu. m (or $ per Cu. Yd.).
Quality Factor Used to control fill operations. When fill material of a given quality is specified, any material with the same or higher quality can be used as fill.
Movement Costs (for all ground types)

Are common to all material types. There are up to 3 haul categories (Freehaul, Overhaul, and Endhaul); this allows you to model up to 3 different types earth moving equipment (for example bulldozer, scraper and truck/excavator) the distance for each type of haul depends on the Hauling and Loading costs.

Haul Costs button allows you to modify these values (also see note below).

  • Hauling Cost (cost to move material) has units of $ per (Cu. m x km) or $ per (Cu. Yd. x mi).
  • Loading Cost (cost to load material prior to moving) has units of $ per Cu. m or $ per Cu. Yd.
Movement Costs Simplified When the simplified check box is set, your options are reduced. You need only specify a loading cost (zero is OK) and a haul cost which is applied to haul longer than a specified Freehaul distance.

Note: For alignment optimization, costs don't need to be exact. The ratio between the costs is what determines the optimal alignment (i.e. the ratio between cut, fill and haul costs). And, even if the total $ cost is not absolutely precise; it can still be used to compare different alignments and options.

You can save your ground table, including costs, to a small file (extension GDX) for use in future optimizations (Save/Open Libraries buttons).

Figure 6: Movement Costs by Class

The graph above shows how the transition distances of 250m and 1500m are calculated in the example.

Movement costs are assumed to be linear with distance; this agrees well with empirical haul equipment productivity data. The haul distance where it becomes cheaper to switch from Freehaul to Overhaul or from Overhaul to Endhaul depends on the intersection of the linear cost graph (see figure above).

The Ground Types dialogue contains information that is common to RoadEng®. It can be accessed from the Alignment Panel using the Options button; it can also be accessed from the Edit |Edit Ground Types menu.

The volume for each distance category is reported in the Alignment Panel as Freehaul, Overhaul and Endhaul.

Optimal Haul

If you have spent any time thinking about the problem of costing road earthworks, you know that calculating the haul cost is not trivial; especially if you have multiple borrow/waste pits and different materials in the ground along the road corridor. Before reporting the haul cost, Softree Optimal solves an optimization problem to determine the lowest cost haul specification that balances material.

  1. Press Cancel to exit the Options dialogue.
  2. File button | Exit. Do not save changes.

Design Time Cost Reporting