Research

Use Of LIDAR To Improve the Highway Location Planning And Design Process

Click thumbnail to enlarge. Figure 1.  Can-do photogrammetry process. Total production time: 24 mo. Total cost $500K. Area: 25 sq mi.

To reduce the time required to plan and design highway projects, highway agencies have begun to streamline processes.  In order to meet the extensive data requirements for environmental assessment and final design, some agencies have chosen to collect and process more terrain data and imagery products than they will ultimately need, in order to be able to rapidly respond to changing location decisions.  While facilitating a smoother, faster planning process, the additional data collection and processing is expensive and time consuming.  For example, a highway bypass study may require as much as $500,000 and 18 months of photogrammetric processing (see Figure 1).

Click thumbnail to enlarge. Figure 2. LIDAR method. Total Production time: 6 mos. Total cost: $200K.  Area: 25 sq mi.

The existing process requires early collection and processing of data to support final design.  However, only the final design stages of project development may require the accuracies provided by conventional photogrammetric processing.  The Iowa DOT proposed that advanced methods of surface mapping (LIDAR) and digital photography may be used for preliminary planning and location issues, limiting expensive and time consuming photogrammetric work to the final alignment corridor.  Further, inherent inflexibilities of aerial photography (leaf-off, high sun angle conditions) required spring flying, was not always convenient for project task sequencing.

Table 1

If LIDAR developed terrain products and digital imagery were sufficient for planning stages, products could be delivered to planners and designers faster at lower costs.  Once final alignment decisions were made, photogrammetric control and processing could be limited to an area perhaps one fifth or smaller than the original location corridor.  This scale of photogrammetric work could be completed in short time at much reduced cost.  Figure 2 shows a representation of the LIDAR enabled process. 

Early estimates indicate a possible savings of 7 months and $250,000.  In order for these savings to be realized, engineers and planners must be able to use the products and resulting designs must be of sufficient accuracy.  The project considered two principal aspects:

1. How would the process to produce terrain and imagery products change, e.g., how could LIDAR and digital photography be introduced into the process (Figures 1 and 2), and
2. How would the substitution of LIDAR for photogrammetry affect accuracy and applicability of resulting terrain and image products.  Specifically, we are testing the accuracy of LIDAR elevation estimates for various surface types (road, ditch, crop areas, forest cover, etc. – see Table 1), and gross estimates of earthwork differences resulting from the use of photogrammetric and LIDAR terrain models (see Figure 3).

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