Preliminary Design Pitfalls: 5 Checks to Avoid Cost Overruns | LRTK

Introduction: Why Is Preliminary Design Prone to Failure?

In civil infrastructure projects, the first step is the preliminary design (gaisan sekkei), an essential stage for determining project feasibility and securing a budget. However, if the design at this early stage is insufficient, the risk of later failures such as major cost overruns, schedule delays, and design changes increases. Because preliminary design plans are developed based on limited information, many uncertainties inevitably remain. If those uncertainties are underestimated or the key points are not addressed and the work proceeds, the later stages will be hit by repeated "unforeseen" events.

In practice, construction sites tend to experience additional work and rework so frequently that people say, "It's rare for construction to finish according to the original contract." The causes vary — unforeseen ground conditions, disputes with neighbors, weather, and so on — but many stem from initial oversights and overly optimistic estimates. There are also frequent cases where a misalignment in understanding among the client, the designer, and the contractor leads to situations of "this wasn't supposed to happen." To avoid these failures, it's necessary to firmly grasp the points to watch during the preliminary design stage. This article provides a concrete explanation of common failures in preliminary design and five points to watch out for.

What is preliminary design? Basic definition and purpose

First, let's briefly clarify what "preliminary design" is. Preliminary design refers to the initial-stage schematic design and construction cost estimation carried out before entering detailed design (final design). For a planned infrastructure project, at a stage when exact drawings and specifications have not yet been finalized, approximate structural planning and quantity estimation are performed based on the information available, and a preliminary estimate of construction costs is prepared. This serves as an important document used for project feasibility assessment, budget requests (preliminary budget requests), or for considering procurement methods.

The purpose of preliminary design is, quite simply, to grasp at an early stage "Can this plan work? Roughly how much will it cost?" For municipal public works, an estimated construction cost is presented to secure the annual budget, and in private development an approximate estimate is also required as material for investment decisions. Therefore, preliminary design requires a reasonably accurate result in a short time, but it is also characterized by large margins of error because the details are not yet determined. In general, the accuracy of preliminary estimates at the early stage is considered to be about ±30–50%, and uncertainty becomes even greater for massive or complex projects. In other words, you must recognize that preliminary estimates are only provisional guidelines and not fixed amounts.

Given the above, preliminary design serves as a compass that determines a project's direction, but depending on its accuracy and assumptions it can also become a dangerous compass that leads the project in the wrong direction. In the next chapter, we will take a detailed look at five common failure patterns and points of caution in preliminary design.

Caution 1: Misidentification of on-site conditions and insufficient surveying

Not accurately understanding the on-site conditions is the most typical cause of failure in preliminary design. It is not uncommon for designers to prepare plans based only on desk-based materials and old drawings, and to proceed while misidentifying on-site conditions such as topography, ground conditions, and existing structures. For example, the following kinds of mistakes tend to occur:

• Misreading topography and quantities: performing earthwork quantity calculations using only old topographic maps or coarse elevation data, causing the actual cut-and-fill volumes to be significantly off. After construction begins it becomes apparent that "there is not enough/excess soil," resulting in major additional hauling in/out and design changes.

• Overlooking ground strength and water table: neglecting preliminary boring or geological surveys and proceeding with standard foundation design even though the site is actually soft ground. Alternatively, designing without assuming a high groundwater table, which leads to the need for additional ground improvement and drainage work after construction starts.

• Insufficient checking of buried objects and existing structures: failing to identify beforehand old structures buried on site (former bridge abutments, box culverts, buried pipelines, etc.), with their existence only discovered later. There are also cases where a high-pressure gas pipeline runs under the planned route, forcing an urgent design change…

These are all problems that arise from insufficient on-site investigation and surveying. In particular, for public works, there is often no time at the preliminary design stage to carry out detailed on-site inspections, or cost estimates are advanced based on a limited set of survey items. However, the cost of that ultimately comes back in the form of additional construction work and budget overruns.

Countermeasure: Be thorough about "going to see the site" and going to collect data. As much as possible, it is preferable for the designer in charge to visit the site personally to confirm the topography and land use. Also, carrying out simple surveys and trial excavations at an early stage will reduce the number of "I wasn't told" factors later on. For example, in one condominium repair project, because the preliminary investigation was inadequate, deteriorated areas of the exterior wall were discovered one after another after construction began, resulting in additional costs on the order of several million yen and schedule extensions (caused by insufficient on-site investigation) [^1]. This is not something that only happens in building repairs; it can occur in civil infrastructure as well. Do not omit on-site verification just because it is the preliminary design stage, and maintain the flexibility to revise plans based on the obtained current-condition data.

[^1]: Introduction of a case in which additional work occurred due to insufficient on-site investigation during a repair job: "If you sign a contract based only on a simple inspection without scaffolding, the risk of additional costs and schedule extensions increases, so implementing a two-stage survey is indispensable." (From a column introducing a failure case by an exterior wall painting company in Saitama)

Note 2: Under- or Over-Design Due to Unconfirmed Design Requirements and Specifications

At the preliminary design stage, the project's required performance and specifications are often not yet finalized. Even on the client's side, while what is to be done may be decided, the question of to what extent it will be done (scale/level) may still be under consideration, and there may be the possibility of future changes as a result of consultations with relevant agencies. As a result, designers are forced to plan based on current assumptions, which carries the risk of underdesign (designs that do not meet the required scale) or overdesign (designs that are more elaborate than necessary).

As an example of under-design, consider a case where the road cross section is decided while future traffic projections are still being reviewed, and later the traffic demand forecast is revised upward, revealing that the design capacity is insufficient. If a road that should have been four lanes was estimated as two lanes, significant redesigns become unavoidable. Conversely, an example of over-design is when, erring on the safe side and providing too much margin, unnecessary scale or functions are incorporated, resulting in higher costs. For example, in a rough estimate for a sewage treatment plant, facility capacity might be calculated at the maximum assumed scale due to uncertainty in future population, but when the demand forecast is later scrutinized it becomes clear that the specification was excessive. In this way, uncertainty in requirements is a double-edged sword, and if misjudged it leads to "built but insufficient" or "over-engineered and over-budget".

Countermeasure: Make uncertain elements explicit and set assumptions. In the preliminary design estimate document, always record the premises, such as "This estimate is based on the conditions of ○○," and agree in advance that the estimate will be reviewed if conditions change later. It can also be effective to consider plans with built-in flexibility. For example, by performing comparative estimates of multiple options and showing "this scale under Condition A, this scale under Condition B," you will be better able to respond flexibly to requirement changes later. In meetings with the client, share that "the specifications at this stage are provisional," and it is advisable to discuss cost impacts of scope changes in advance. In short, the key is not to proceed while leaving matters that are not yet determined ambiguous. Since the design is based on assumptions, all stakeholders need to understand that "if the assumptions change, the results will change as well."

Note 3: Overreliance on Past Unit Prices and Reference Examples

At the rough estimate stage, detailed cost estimates cannot be prepared, so estimates are inevitably made with reference to past cases and standard unit prices. This is generally an effective method, but do not be overconfident. Relying too heavily on past data can lead to incorrect estimates that are not suitable for the current project.

A common case is when people take old unit prices or similar construction costs at face value. For example, if you used public construction unit prices from five years ago or internal performance data as-is to make a rough estimate, recent surges in material prices and labor costs could actually result in a cost increase of more than 20%. In recent years, prices for steel and fuel have fluctuated widely, and construction labor unit prices are updated every year. The easy assumption that 'It used to be ○○ yen/㎡ (yen/ft²), so it will be about the same this time' is very dangerous. You should also consider geographic and environmental differences. Applying urban construction costs to a rural site, or vice versa, can lead to large errors because of differences in land acquisition costs, transportation costs, labor conditions, and so on.

Overreliance on reference examples can also be a pitfall. For example, using the design of a previously successful similar project as a template can lead you to overlook the unique conditions of the current project. You might have assumed it was fine because the last site was flat, only to find this time the terrain is highly undulating and additional construction methods are required; or you may have reused a standard specification that, in reality, is difficult to implement under the actual site conditions; and so on. Because each project has different conditions, it is important not to think "it's fine because there is a precedent" but to always perform adjustments and verifications to match the current conditions.

Countermeasure: Treat past data as only a reference and adjust it with the latest information. It's true that accumulated past data is helpful for rough estimates, but be sure to check the latest unit price data and market trends. For public works, verify unit prices using the latest "Estimation Standards" and materials from the "Construction Price Research Association", and, if necessary, add an amount to cover price increases. Also, when referring to past similar projects, it is indispensable to identify the differences between that project and the current one. Compare them from perspectives such as how the scale differs, whether ground conditions are the same, and whether design standards or regulations have changed — and correct parts that cannot be dealt with by simple scaling. In short, use past data as a reference but do not take it at face value. While basing decisions on data, apply realistic judgment and aim for a reliable rough estimate.

Point 4: Overlooking Legal Regulations and Occupancy Restrictions

Infrastructure design is always subject to laws and regulations. If these are overlooked and preliminary estimates are carried forward, it may later be discovered at the permitting stage that "this design cannot be approved" or "it does not meet the standards," causing significant rework. Also, restrictions on space use, such as road occupancy and river occupancy, must be identified in advance, otherwise construction may not be possible as planned.

A typical example of a regulatory oversight is noncompliance with design standards and safety standards. For example, in road design there are standard values and structural requirements to be followed, such as the Road Structure Ordinance and each municipality’s road design guidelines; for bridges, seismic design standards; and for drainage facilities, water quality environmental standards. If you proceed from the preliminary estimate stage without checking these, thinking “we can adjust during detailed design later,” it may turn out that the original plan cannot be approved due to insufficient carriageway width or excessive gradient. Restrictions related to urban planning and land use laws (such as the City Planning Act, the Agricultural Land Act, and the Forest Act) are also important. For example, if the planned site is in an urbanization control area, permission is required even for the construction activity itself, and in cultural property protection zones or areas regulated under the Natural Parks Act, construction methods and layout may be restricted. If you ignore these when drawing up plans, you will be forced to change the design at the stage of permit application.

Overlooking occupancy restrictions is also troublesome. When using public property, prior permission or consultation is required, such as the road occupancy permit under the Road Act or the river occupancy permit under the Rivers Act. For example, installing structures on a road or burying a pipeline that crosses a road requires permission from the road administrator, but if such requirements are not considered in preliminary design and costs are estimated with a “plan to run a pipe here,” additional costs later arising from permit conditions (night work, occupancy fees, etc.) or, in some cases, route changes may occur. Crossings with railways and other infrastructure also require caution. There are cases where a sewer pipe planned to pass under a railway ended up requiring double lining or special construction methods as a result of consultations with the railway operator, leading to higher-than-expected costs.

Countermeasure: List and verify relevant laws and permit conditions in advance. At the stage of starting the design, identify the laws, ordinances, and consultation counterparts that may be related to the project. They may extend across many areas—roads, rivers, water supply and sewage, farmland, forests, urban planning, environmental assessments, etc.—but at a minimum consult the responsible departments to check whether they apply. In the preliminary design document, it is reassuring to include a note such as "This plan may require permission under the XX Act; depending on the conditions, changes may be necessary." Also, review the latest design standards and, in broad terms, confirm whether they conform. Especially for items likely to be designed close to the limit values (slope, width, height restrictions, etc.), it is wise to also consider a slightly more relaxed alternative to avoid problems later. Clearing legal regulations is a basic prerequisite for advancing a project. Because "not knowing" is not an excuse, be aware of this from the initial stages.

Note 5: Adjustment items and anticipated consultations with landowners are not reflected

Infrastructure construction, by its nature, requires coordination with many stakeholders. Neighboring residents, landowners (land rights holders), other infrastructure operators (electricity, gas, telecommunications, etc.), and even local residents and environmental groups — depending on the project, there are various parties to consult. A common failure in preliminary design is planning without taking such coordination matters into account.

A typical example is difficulty in land acquisition. If the planned site includes privately owned land, negotiations with the landowners will inevitably arise. Even if at the preliminary stage you draw a route on paper and think “acquiring the land around here will be fine,” once negotiations begin you can encounter higher-than-expected hurdles such as surging land acquisition costs, provision of substitute land, and sometimes the need to respond to opposition movements. However, because such risks are often not factored into preliminary estimates and both land costs and the timetable were optimistically estimated, the plan can later be threatened with collapse.

Also, coordination with existing public utilities is often overlooked. When road widening or sewer works require the relocation of utility poles and overhead lines, consultations and construction coordination with the relevant power companies and telecommunications companies are necessary. If those adjustment construction costs and schedules are ignored in the rough estimate, additional expenses such as 「pipe relocation works」「temporary bypass facilities」 may be incurred at the execution stage, and the construction period may be extended. Furthermore, commitments with the local community, such as local briefings and environmental protection measures, are also important. If agreement items are added later—for example, installing noise barriers as noise and vibration countermeasures or restricting the hours when construction vehicles may pass—this will affect the construction plan and costs.

Measures: Identify consultation items with stakeholders and incorporate risks. List stakeholders who are likely to be involved in the project and, for each, consider what consultations or approvals will likely be required. For example, write down anticipated items such as "a prior explanation to the ○○ district residents' association is necessary," "possibility of borrowing part of land owned by △△ Corporation," "coordination with the ○○ Waterworks Bureau for relocation of water pipes," and so on. On top of that, evaluate the impacts if consultations become protracted. Prepare alternatives (route changes or structural modifications), allocate contingency funds, and build in schedule slack. Of course, at the rough estimate stage you cannot predict everything accurately, but there is a big difference between "not considering it at all" and "having at least some anticipation." Especially for land acquisition negotiations, they typically require significant time and cost based on experience, so you should coordinate early with the specialized department and develop a strategy. Local coordination is the key to project success. Get into the habit of considering negotiation plans with people and organizations alongside technical design.

Summary: How to Properly Utilize Preliminary Design

As described above, preliminary design involves numerous uncertain elements and easily overlooked points. Misinterpretation of site conditions, undefined performance requirements, incorrect application of data, omissions in regulatory checks, and delays in stakeholder coordination — these are all common pitfalls, but conversely they are things that can be prevented if addressed in advance. By firmly addressing these cautions at the preliminary design stage, you can reduce major course corrections later in the process and keep the project moving smoothly.

Finally, let's summarize the points for correctly utilizing preliminary design:

• Clarify the assumptions: Always document and share the conditions that form the basis of the estimate (such as ground conditions and required specifications) with stakeholders. Agree in advance to review the estimate if those conditions change later.

• Incorporate risks and uncertainties: For unknowns and elements that may change in the future, provide appropriate contingency (reserve). Consider the range between optimistic and pessimistic scenarios, and estimate the impact in the worst case.

• Communication with stakeholders: Do not let designers work in isolation; actively coordinate with the client and other departments. In particular, share and confirm policies early for coordination items and permit/approval issues.

• Ongoing updates: An estimate is not finished once it is produced; it should be updated as the project progresses. When new information (such as survey results or negotiation outcomes) becomes available, revise and refine the estimate each time to always reflect the latest situation.

Preliminary design is both the project's compass and an adjustment valve. Its mission is not to deliver a perfect answer from the start but to provide a reasonable basis for decision-making while anticipating future uncertainties. For that reason, it is important to plan based on reliable information and calm judgment, taking into account the cautions listed here. Appropriate preliminary design will smooth subsequent detailed design and construction, and ultimately become a powerful guide leading to project success.

Bonus: Getting Started with LRTK for On-site Inspections and Simple Surveying

To increase the accuracy of preliminary design and prevent failures, the key is how accurately you can gather site information in the early stages. That said, outsourcing detailed surveys and investigations to external parties for every project takes time and money. What is attracting attention now is tools that let you easily obtain on-site survey data. One such system is LRTK（エルアールティーケー）. As a cutting-edge tool that has recently been gaining attention among civil engineers, some of you may already be familiar with it.

What is LRTK? Put simply, it is a groundbreaking device that transforms a smartphone into a high-precision surveying instrument. It is used by attaching a dedicated compact GPS receiver (antenna) to an iPhone or similar device, and leverages satellite positioning RTK (real-time kinematic) technology to improve position information that would normally have errors of several meters with a typical smartphone GPS to an accuracy of a few centimeters (a few inches). In addition, by integrating with the smartphone's built-in LiDAR sensor and camera, it delivers an all-in-one set of practical surveying functions for field use, such as three-dimensional point cloud data measurement, on-site earthwork volume calculation, and coordinate navigation to target points. In short, if you put this single device in your pocket and go to the site, you can quickly perform on-site inspections and measurements by yourself that previously would have required organizing a surveying team and bringing equipment.

Benefits LRTK Brings to On-site Verification During the preliminary design stage, there are frequent needs such as "I want to quickly measure the site" or "I only want to know the height or distance of this point." Using LRTK, for example, you can continuously measure elevations along a planned route in a short time, record land boundary positions on the spot, or instantly measure the distance to a potential obstacle with a laser, allowing you to obtain exactly the "data you wanted" right there on site. The survey data you collect can be overlaid on maps or drawings on a smartphone and can also be saved to the cloud for team sharing. This enables you to continue discussions back at the office based on accurate current site data, reducing later discrepancies such as "it turned out different from what I expected."

Additionally, LRTK's ease of use for anyone is a major advantage. While traditional surveying instruments required specialized knowledge, LRTK is designed so you can launch a dedicated app and start positioning with a single tap, and intuitively take points or perform scans. Because it is easy for technicians with limited field experience to handle, it enables collecting on-site data as an extension of everyday tasks. This will be useful not only for preliminary design but also for construction management and maintenance.

In summary, the top priority for avoiding failure in preliminary design is to know the site. As a means to that end, simple surveying using LRTK can be an extremely powerful helper. If you haven't used it yet, why not try it once on site? You'll surely be surprised—"Can you really obtain such accurate site information so easily?!"—Make good use of technological advances to enable highly accurate preliminary design and smooth project progress. At your site too, LRTK will be a powerful ally for fail-proof design.