A time–distance diagram is a chart with two axes: one for time, the other for location. The units on either axis depend on the type of project: time can be expressed in minutes (for overnight construction of railroad modification projects such as the installation of switches) or years (for large construction projects); the location can be (kilo)meters, or other distinct units (such as stories of a high-rise building).
Normally, the time axis is drawn vertically from top (start of project) to bottom (end of project), and the location axis is drawn horizontally. The direction of the chainage is usually chosen with consideration of geographical position of the project, with the numbers either increasing or decreasing. The location axis is often enhanced with a schematic of the construction project. Other, location-specific information (aerial photos, cross-sectional views) can be added to enhance the visualization of the work site.
A legend explaining the meaning of the various colors, symbols and line types used in the chart may be included in the time–distance diagram. Other information shown may be cost and resource histograms along the time axis.
The drawing area may contain grid lines to ease comprehension of the chart: hours, days, weeks, months, years, for the time axis; equidistant units along the distance axis or specific locations (piles, stations, foundations, etc.). The background of the drawing area may be enhanced with time and location related information such as close seasons, hold-off intervals, meteorological data (rain/snow fall, temperatures).
The project activities are placed within the drawing area according to their specific nature:
Annotations such as boxed text and activity labels within the drawing area improve the level of information.
Time–distance diagrams can be created using any kind of drawing tool, certainly one which allows scaled drawing (for example, CAD editors, Visio). Sometimes, spreadsheet tools are employed where the width of the columns and the height of the rows form the distance and time scales.
However, in real project life, a time schedule needs to be adjusted continuously: This is when the use of specialized tools quickly brings out their advantage. These tools (see External links below) are project management tools in their own right with an emphasis on the ability to present the time schedule as time–distance diagram. Activities can be edited using project management terminology plus all drawing attributes for the activity's shape. Special features allow dependency links (with lags), complex scaling, access conflict detection, resource-dependent progress, and more. Most often, such tools provide various interfaces to other project management software, at least to import and export activity information. Complex systems (such as TimeChainage, DynaRoad, TILOS or Time Location Plus) even integrate into commonly used project management software (Primavera, Microsoft Project, Asta Powerproject).
from projects using time-distance diagrams)
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