A traverse party may vary from 2 to about 12 personnel, all under the supervision of a traverse party chief. It usually consists of a distance-measuring crew, an angle crew, sometimes a level crew, and other support personnel. This break-down of personnel is ideal; but, on many occasions, the same personnel will have to perform a variety of tasks or functions. Therefore, each party member is trained to assume various duties and functions in several phases of the work survey.

Whenever possible, a reconnaissance must be made to determine the starting point, the route to be followed, the points to be controlled, and the closing station. When selecting the starting and closing points, you must select an existing control station that was determined by a survey whose order of accuracy was equal to or greater than the traverse to be run. When running a traverse in which the direction of the traverse lines are not fixed before the start, select a route that offers minimum clearing of traverse lines. The best available maps and aerial photographs should be used during the office and field reconnaissance. By selecting a route properly, you can lay out the traverse to pass relatively close to points that have to be located or staked out.

On other surveys, such as road center line layout, the directions of the traverse lines are predetermined, and all obstructions, including large trees, have to be cleared from the line. Often the assistance of the equipment and construction crews is needed at this point. For the lower order surveys and where taping is used, the exact route and station locations normally are selected as the traverse progresses. These stations have to be selected so that at any one station, both the rear and forward stations are visible, and only a minimum number of instrument setups is kept, reducing the possibility of instrument error and the amount of computing required.

Furthermore, the electronic distance-measuring devices (EDMs) have made traverse reconnaissance even more important. The possibility y of using an EDM should be considered after the general align-ment in direction and the planned positioning of stations. A tower or platform installed to clear surface obstruction will permit comparatively long optical sights and distance measurements, hence avoiding the necessity of taping it in short increments.

Some station marks are permanent markers, and some are temporary markers, depending upon the purpose of the traverse. A traverse station that will be reused over a period of several years is usually marked in a permanent manner. Permanent traverse station markers are of various forms, including such forms as an iron pipe filled with concrete; a crosscut in concrete or rock; or a hole drilled in concrete or rock and filled with lead, with a tack to mark the exact reference point. Temporary markers, on the other hand, are used on traverse stations that may never be reused, or perhaps will be reused only a few times within a period of 1 or 2 mo. Temporary traverse station markers are usually 2-in. by 2-in. wooden hubs, 12 in. or more in length. They are driven flush with the ground and have a tack or small nail on top to mark the exact point of reference for angular and linear measurements. To assist in recovering the hub, a 1-in. by 2-in. wooden guard stake, 16 in. or more in length is driven at an angle so that its top is about 1 ft over the hub.

Keel (lumber crayon) or a large marking pen is used to mark letters and/or numbers on the guard stake to identify the hub. The marked face of the guard stake is toward the hub. Since many of the hubs marking the location of road center lines, landing strips, and other projects will require replacement during construction, reference marks are placed several hundred feet or meters away from the station they reference. Reference marks, usually similar in construction to that of the station hub, are used to reestablish a station if its marker has been disturbed or destroyed.

NOTE: Procedures for marking hub and guard stakes for traverse stations, road center line layout, and other surveys are presented in the next chapter.

As we discussed earlier in this chapter, the starting point of a closed traverse must be a known position or control point; and, for a closed loop traverse, this point is both the starting and closing point. Closed connecting traverses start at one control point and tie into another control point.

A traverse starting point should be an existing station with another station visible for orienting the new traverse. The adjacent station must be intervisible with the starting point to make the tie easy. If you do not find the adjacent station easily, you should observe an astronomic azimuth to orient the starting line, and then continue the traverse. Any existing control near the traverse line should be tied in to the new work.