Structural Design and Approval

Responsibilities of the Structural Design and Approval Division include:

Ensure the structural integrity and safety of 670 public bridges and some retaining walls throughout the County
Biannual bridge inspections
Issue and review temporary bridge overload permits
Provide support to other agencies as needed with retaining walls, buildings and bridges within the park system
Developing maintenance and construction programs

Biannual Bridge Inspections

All bridges which span lengths over 20 feet are required to be inspected every two years by Federal law. These inspections must comply with the Federal Highway Administration's National Bridge Inspection Standards. The costs for these inspections are covered 100 percent by Federal funds. Baltimore County follows the same procedures for their minor bridge structures (those between eight and 20 feet.) The inspections for the minor bridges are funded by the County, and when available, State aid. The County also maintains an on-call maintenance contractor for repairs and minor replacement projects.

Bridge Design Criteria

The American Association of State Highway and Transportation Officials (AASHTO) maintain the building codes for both roadway and bridge construction in the United States.

For roadway bridges—We refer to the AASHTO Standard Specifications for Highway Bridges manual and it's successor the AASHTO Load Resistance Factor Design Bridge Design Specifications, which provided criteria governing the structural engineering and geotechnical aspects relating to bridge design.
For roadway widths over bridges—Both the above manuals refer to the AASHTO Policy on Geometric Design of Highway and Streets. This document governs road design. These criteria were incorporated into the Baltimore County Design Standards and Policies for Rural Baltimore County roads.

Factors Determining Width

Bridge widths are determined by six factors:

Functional classification—Defines roads according to the character of service they are intended to provide. Most County roads are classified as local, collector or arterial roads.
Average daily traffic volumes—This data is maintained and provided by the Bureau of Traffic Engineering and Transportation Planning. 20-year predicted counts are also developed and incorporated into the bridge design.
Percent trucks—Provided by the Bureau of Traffic Engineering.
Design speed—Determined by the provided guidance of AASHTO for different types of roadways.
Geometric conditions—Relates to the existing alignment of the roadway across the structure. For bridge replacement projects, we look to do the least amount of approach roadway work possible to meet the minimum design criteria. Occasionally a bridge needs to be slightly wider to accommodate the curved roadway or for safety reasons relating to line of sight requirements.
Community input—Provides us with information relating to local conditions and concerns of citizens impacted by the replacement of an existing bridge.

Factors Determining Length

Bridge length is based on the needs of the feature crossed:

Bridges over streams—Sized on hydraulic characteristics of the stream passing through the crossing.
Bridges over railroads—Sized by the clearance enveloped required by the railroad.

Bridge Replacement

The decision to replace a bridge is based on the findings of the biannual inspection reports. Once County engineers determine a structure needs to be replaced:

This initial engineering stage consists of data collection (traffic volumes, location of existing right of way and adjacent property lines, wetland delineations, field surveys etc.).
A preliminary investigation of type, size and location plans, are developed. These documents represent about 30 percent of the engineering phase of the project. It is during this preliminary design phase that the full extent of the project is developed and community input is solicited. Most replacement bridges are sized hydraulically in-kind such that the flood characteristics of the new match those of the existing structure. Some replacement bridges and all new structures on new roadways are sized to pass certain storms based on the design of the roadway. The same design criteria, right of way acquisition process and environmental review regulations and permitting process are followed regardless of the funding source.
Once a consensus is achieved, a final design is undertaken to complete the construction documents for bid.
County engineers prioritize replacement candidates based on structural condition, ability to repair effectively and economically, and availability of funding.

Funding

When Federal funds are used, projects must be reviewed by the Maryland State Highway Administration. There is also some additional environmental review documentation required on Federal aid projects.

Bridges under 20 feet in length are 100 percent funded by the County. Occasionally, a bridge over 30 feet long will be replaced using 100 percent County funds, however Baltimore County is committed to using Federal funding whenever possible.
Bridges over 20 feet in length and meeting certain criteria qualify for Federal Bridge Replacement funds. These Federal funds pay for 80 percent of the design and construction costs associated with a project.

Learn More

Once a year the Division of Engineering and Construction conducts an open workshop to receive public input on all projects location outside the County's Urban Rural Demarcation Line. Public meetings may also be conducted for individual projects. Bureau of Engineering personnel are available to speak at civic groups by appointment.

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