Improvement plans (also called public improvement plans, civil improvement plans, or PI plans) are the construction documents for infrastructure that will be dedicated to the public or built within the public right-of-way. Streets, sidewalks, curbs, water mains, sewer mains, storm drains, and street lights are all public improvements. The improvement plans tell the contractor exactly what to build, and the public works department uses them to inspect the work and eventually accept the infrastructure for public maintenance.
When Improvement Plans Are Required
Improvement plans are required whenever a development project triggers the construction of new public infrastructure or the modification of existing public infrastructure. Common triggers include:
- Subdivision maps. Both tract maps and parcel maps typically have conditions requiring improvement plans for new streets, utilities, and drainage within and adjacent to the subdivision.
- Building permits for new construction. Even without a subdivision, a new building may trigger frontage improvements (new sidewalk, curb and gutter, driveway approach, street trees) and utility connections.
- Encroachment permits. Any work within the public right-of-way (street cuts for utility connections, driveway construction, sidewalk replacement) requires plans approved by the public works department.
- Conditions of approval. Planning approvals (site development permits, conditional use permits, design review) often include conditions requiring specific improvements.
What the Plans Include
A typical set of improvement plans includes the following sheets:
| Sheet Type | Contents |
|---|---|
| Title sheet | Project name, location map, index of sheets, general notes, legend, agency signatures |
| Demolition plan | Existing improvements to be removed (pavement, curb, sidewalk, utilities) |
| Street plan and profile | Horizontal alignment, vertical profile, curb and gutter, sidewalk, pavement section, ADA ramps |
| Grading plan | Existing and proposed contours, spot elevations, drainage arrows, slopes, earthwork quantities |
| Water plan and profile | Water main alignment, pipe sizes, fittings, valves, hydrants, service connections, profile with cover depths |
| Sewer plan and profile | Sewer main alignment, pipe sizes, manholes, service laterals, profile with slopes and inverts |
| Storm drain plan and profile | Storm drain pipes, catch basins, manholes, outfalls, profile with slopes and inverts |
| Signing and striping | Pavement markings, regulatory signs, street name signs, stop bars, crosswalks |
| Erosion control / SWPPP | Temporary BMPs during construction, staging areas, construction entrance |
| Details | Standard details for curb, gutter, sidewalk, ADA ramps, manholes, trenching, pavement sections |
Who Prepares Them
Improvement plans must be prepared by a licensed civil engineer (PE) registered in the state where the project is located. The engineer stamps and signs every sheet. In most jurisdictions, a licensed land surveyor must also stamp and sign sheets that show property boundaries, rights-of-way, and easements.
The Review Process
First Submittal
The engineer submits the improvement plans to the public works department (or city/county engineering department) for review. Most jurisdictions require multiple printed sets plus a digital (PDF) submittal. A plan check fee is required at submittal, typically calculated as a percentage of the estimated construction cost (commonly 3-5%).
Plan Check Comments
The reviewing agency returns plan check comments, typically within 4-8 weeks for the first review. Comments come from multiple reviewers: public works engineering, water district (if separate), sewer district, fire department, traffic engineering, and stormwater/environmental compliance. The civil engineer must respond to every comment with a revision or explanation.
Resubmittal
The engineer revises the plans and resubmits. Second and subsequent reviews are usually faster (2-4 weeks). Most projects require 2-3 review cycles before approval. Complex projects may require 4 or more cycles.
Approval for Construction
Once all comments are resolved, the plans are approved for construction. The reviewing agency stamps the plans and returns approved copies to the engineer and developer. Construction cannot begin on public improvements until the plans are approved and other prerequisites are met (bonds posted, insurance provided, pre-construction meeting held).
Design Standards
Improvement plans must conform to the local jurisdiction's design standards and standard details. These are typically published as a "Standard Plans" or "Standard Details" manual and a "Design Standards" or "Design Criteria" manual. Key standards include:
- Street geometry: Lane widths, curb radii, sight distance, vertical curve criteria (AASHTO A Policy on Geometric Design of Highways and Streets).
- Pavement design: Structural section based on traffic index and subgrade R-value (Caltrans Highway Design Manual or local equivalent).
- Water system: Pipe materials, minimum pipe sizes, minimum cover, valve spacing, hydrant spacing (AWWA standards and local water district standards).
- Sewer system: Pipe materials, minimum pipe sizes, minimum slopes, manhole spacing (local sewer district standards).
- Storm drain: Design storm frequency (10-year or 25-year), pipe materials, minimum pipe sizes, inlet types (local standards).
- ADA compliance: Curb ramp design, sidewalk cross-slopes, accessible routes (Public Right-of-Way Accessibility Guidelines, PROWAG).
Bonds and Security
Before construction begins (or, in some jurisdictions, before the subdivision map is recorded), the developer must post improvement bonds. These bonds guarantee that the improvements will be completed as shown on the approved plans. There are two types:
- Faithful performance bond: Guarantees the improvements will be completed. Typically 100% of the estimated construction cost.
- Labor and material bond: Guarantees that subcontractors and suppliers will be paid. Typically 50-100% of the estimated construction cost.
The civil engineer prepares the cost estimate that determines the bond amounts. This estimate must cover all public improvements shown on the plans, including contingency (typically 10-15%) and engineering/inspection fees (typically 10-15% of construction cost).
Inspection and Acceptance
During construction, the public works department inspects the work at key milestones: subgrade preparation, pipe bedding, pipe installation, backfill and compaction, aggregate base, paving, and final punch list. The contractor must call for inspections at each milestone. Work that proceeds without inspection may be required to be removed and reconstructed.
After construction is complete and the punch list is cleared, the developer requests acceptance of the improvements by the city or county. A warranty period begins (typically 1-2 years) during which the developer is responsible for any defects. After the warranty period, the jurisdiction accepts maintenance responsibility for the public improvements.
When Improvement Plans Are NOT Required
- Private site work only. If the project does not involve any work within the public right-of-way or any public utility extensions, improvement plans are not required. The site civil work is shown on the building permit plan set instead.
- Minor utility connections. Some jurisdictions allow simple water meter installations or sewer lateral connections with an encroachment permit application and a standard detail reference, without full improvement plans.
- Maintenance and repair. Routine maintenance of existing public improvements (pothole patching, valve replacement, hydrant painting) is done by the maintaining agency and does not require improvement plans.
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