Chapter 6 - Alignments
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Training Materials
6.1 Background
The Michigan Department of Transportation defines a road alignment as a series of tangents and geometric curves incremented in 100 foot stations that defines the location and direction of the roadway or proposed roadway improvement.
Most Michigan roadways were first laid out and created 75 to 100 years ago or more. Generally, since that time, several road improvement projects may have been conducted on these roads using various methods of establishing the route location and acquiring property. Because of this, it is important to determine which alignment was used to acquire the original Rights-of-Way. It is also important to identify and re-establish alignments used on the subsequent construction projects conducted since that time as they may impact the current project. In some cases, multiple alignments along the same route over differing time periods have been used to purchase property. It is, therefore, important to carefully research and substantiate the previous alignments and supporting documents used to describe and acquire property for improvement projects conducted over a particular route. Field evidence in addition to record documents is key to this verification process and further assists in redefining the design and/or physical location of the roadway.
Typically, there are three different types of data described as "Horizontal Alignments" that are used for MDOT design, any of which may or may not be considered a legal alignment. These three types of alignments are: Survey, As-Constructed, and Construction. Any or all of these three may have been used as a legal alignment in the past. When re-establishing legal alignments, it is the surveyor's responsibility to gather and evaluate all the evidence necessary to determine the original location of the pertinent alignments for the specific project area. Alignments must be discussed fully in the Surveyor's Report, see Chapter 4.2 Alignment / Right Of Way Survey for additional information. All alignments must be referenced to the coordinate system of the project. The following definitions briefly describe in sections below:
6.2 Survey Alignment
Historically, a survey alignment was primarily used as a baseline for locating topographic features, cross-sections, etc., along a proposed route. This was an alignment provided to or created by survey crews to lay out a preliminary location and collect data relative to that route. The design of roads and bridges was developed from the topography tied to these alignments. Frequently the construction alignment developed by the design engineer would vary from the survey alignment. It is important to understand that determining which of these two alignments the legal alignment is will depend upon which alignment was used to describe the Right of Way parcels.
Frequently the construction alignment has become the legal alignment, as it has been the general policy of MDOT Real Estate personnel to describe parcel conveyances from the construction alignment. If the Survey Alignment is provided as a historical reference, it may be re-traced from data recorded on historic (or original) plans, ROW sheets, previous surveys or other sources.
Unless explicitly defined otherwise, the survey alignment should NOT be considered a legal alignment and new parcel takes should NOT be described from a survey alignment.
6.3 As-Constructed Alignment
This is frequently referred to as a "best fit" alignment, which represents the current physical road location. These alignments are typically computed using survey points collected along the actual roadway centerline (crack, crown, paint stripe, curb split, etc.). The points are used to compute best fit tangents and curves using data processing algorithms designed for such purposes, hence the reference to "best fit". The curves and tangents are usually compared to record alignment data from old plans and adjusted to create an alignment that best approximates both the intended construction alignment and the actual location where the road was placed during construction (as-constructed). Stationing is usually matched to existing plans. An as-constructed alignment is primarily used to give the designer a sense of where the actual roadway lies and to provide a baseline for survey and design.
The physical center of the existing road is considered evidence but does not necessarily define the legal alignment, unless specifically called for in a conveyance. The rationale used to determine this alignment, as well as it's standing (legal, non-legal) should be clearly explained in the alignment section of the surveyor's report.
The term "as-constructed" may also refer to a historic alignment location that is not related to the current physical centerline of a roadway. When retracing alignments that are referenced on older conveyances (with terms such as: "as now surveyed," "as now established," "as now surveyed and constructed" etc.), a present day retracement involves the determination of the old road location at the time of conveyance (e.g. "1932 as-constructed alignment") which often varies considerably from the present day physical centerline of the roadway. This often involves extensive consideration of historical evidence pertaining to the conveyance itself. This evidence may be in the form of field measurement, purchase agreements, marked final Right of Way plans, survey notes, etc.
6.4 Construction Alignment
An alignment (horizontal and vertical) developed for the purpose of constructing a roadway. The construction alignment is proposed by an engineer. As the design of the project is based upon the construction alignment, any additional ROW needed for the project was frequently described from this line.
Add Link to the Geometrics section of the RDM
6.5 Legal Vs. Non-Legal
A legal alignment defines actual location of the Right of Way based on either a survey alignment, as-constructed alignment, and/or a construction alignment as referenced in property descriptions, conveyances, i.e. legal documents. It is considered a property controlling entity similar in standing to government section lines. Often, the description of this line is used as part of these descriptions. A survey to re-establish the location of the legal alignment is absolutely necessary when the purchase of additional ROW is required. Re-establishing a legal alignment is considered a boundary determination since the existing Right of Way is defined by, and described from, the legal alignment.
As described above, there may be several "legal" alignments on any particular project from which different parcels have been purchased over time. Considerable research and survey work may be required. Retracement of a legal alignment restores and perpetuates the original location of the Right of Way for a particular portion of a route, from a particular time period, and a specific property acquisition. Right of Way plans, conveyance, previous construction plans, existing monumentation including Public Land Survey System (PLSS) corners (see Property Section), and other recorded and physical evidence is used to determine the proper location of the legal alignment. It should be understood that the legal alignment and the physical location of the roadway may vary considerably. When performing legal alignment surveys, the relationship of the legal alignment and the physical centerline should be clearly defined. Generally if property is purchased, the Departments past policy has been to describe the conveyance from the construction alignment, potentially creating yet another "legal" alignment.
In order to minimize the creation of multiple legal alignments and thereby the confusion and added cost of future surveys, future ROW acquisitions should be based on previously established legal alignments whenever possible. It is left to the judgment of the Real Estate personnel to determine when it will be necessary to utilize the construction alignment for ROW acquisition descriptions. It is strongly recommended that the assistance of the project Professional Surveyor be employed for this determination.
An alignment that is designated as a non legal is used primarily to locate features for the purpose of design. It can be considered a line that provides direction and stationing for locating features, determining quantities, and staking out the project. A non-legal alignment is not intended to relate to the location of the Right-of Way and is not used for property acquisition