Visualization techniques are used to assist in the decision regarding design choices and can be anything from renderings to photo-simulations.
Visualization techniques are powerful tools to assist in the decision regarding design choices. For example, the Minnesota DOT utilized visualization in one study of alternative cross section design values for a highway through a sensitive park area. As shown in Exhibits F-12 (CSD_500-505), the different values for lane and shoulder width, and for type of roadside design (curb and gutter versus open section) produced different visual impacts and effects on number of trees to be removed. The Connecticut DOT employed visualization to demonstrate the visual impacts and enhancement opportunities associated with alignment alternatives for a road through a town. Finally, visualization is even being used in complex interchange projects to demonstrate construction phasing schemes. The Wisconsin DOT, in a project involving reconstruction of a $500 million interchange in Milwaukee, is employing visualization for such purposes.
Visualization to Review Alternative Solutions for Rural Highway Design Project in Minnesota
Visualization techniques can also be used to show the effects of different arterial cross section designs, or to demonstrate a streetscape or roadside treatment proposal. For a project in Denver, Colorado, a hotel owner was concerned about the potential blocking of a view of the Rocky Mountains from guest windows by a proposed ramp overpass. Visualization enabled the Colorado DOT to demonstrate that the design would not create a visual barrier from the windows in question. Exhibit F-13 (CSD_161) shows four design alternatives for an arterial project in Washington state.
Use of Visualization to Demonstrate Different Access Concepts for a Suburban Arterial in Washington
There are different types of visualizations, from renderings over photographs to three-dimensional images generated from design files and digital terrain models. The latter require more preparatory work (the proposed functional design must be completed first in both plan and profile), but are visually true to scale. Also, it is possible to readily generate countless images from different angles and eye locations. The former are relatively simple and easy to generate, but care must be taken to represent the true visual character. A rendering would apply to one view from one location. Exhibit F-14 (CSD_183) shows an example rendering from a freeway project in Missouri.
Photo Rendering of Rural Freeway Project in Missouri
Visualization has become a standard practice for many DOTs. Indeed, public and stakeholder groups once shown visualizations expect them on every project after the first one. Pilot states have recognized the need to have capable staff and the appropriate computer software to incorporate visualizations on their projects.
Traffic Operational Simulation
In many cases, traffic operational issues are a concern either to technical stakeholders or the general public. Traffic operational concepts are difficult even for technical professionals to grasp. The effects, for example, of increased traffic on queuing, delay, and operations are not linear, and are often not well understood. Simulations showing the effects, for example, of no action but increases in traffic can be powerful tools for demonstrating the expected need for a mobility solution.
Simulation of vehicles or vehicle streams through complex locations such as closely spaced intersections, or through roundabouts, is a useful tool to demonstrate operations. With respect to new solutions such as roundabouts, some agencies have found it useful to demonstrate their operation where a roundabout is proposed for the first time in an area. The Iowa DOT used a VISSIM simulation of roundabout operations to explain to the public how they worked, and found it to be valuable for a project in Ottumwa, Iowa. The Ottumwa VISSM, along with examples of additional simulations, are in included in Appendix F.
Best practices include FHWA's CORSIM model (which provides detailed quantitative output and animation of traffic operations through an integrated network comprised of arterial streets and freeways). Other software tools include VISSIM, Paramics, and Synchro. The greatest value can be obtained from simulations where calibration (i.e., replication of operations as they occur and are observable by stakeholders) is possible. Simulation then can be particularly effective in showing, for example, the queuing and resulting other problems that might occur if no action were taken and traffic increased.