Honors College

Document Type

Honors Thesis

Publication Date

Spring 2014


The purpose of this thesis is to study a wide range of historic bridges along the coast of Maine. Three bridges were selected for study: Sewall’s Bridge, Bailey Island Bridge, and Deer Isle-Sedgwick Bridge. The selected bridges exhibit varying historic treatment approaches, material use, structure type, and span length. This thesis establishes the compliance of these bridges with modern geometric standards, as defined by AASHTO (2011), including maximum grade, vertical and horizontal alignment, roadway width, and sidewalk width. Passing sight distance, passenger comfort and general appearance are not be included in this evaluation of geometric design.

This document outlines the standards for defining historical significance of bridges; gives a summary of the three studied bridges including project area, history and significance, and structural features; explains the modern geometric design requirements; evaluates the bridges based on these design requirements; and makes recommendations to remedy the inconsistencies between the bridges’ current geometric design and the geometric design requirements outlined by AASHTO (2011).

A Policy on Geometric Design of Highways and Streets (AASHTO, 2011) is the guiding principal for the design of roads with regard to geometric standards. Various equations, tables, and graphs within the text quantify these standards. These measures are used within this thesis to determine the required geometric design values according to modern design principals and compared with the existing values of the three bridges using scaled bridge plans.

The evaluation of the studied bridges shows that all three bridges are compliant with the AASHTO (2011) guidelines for maximum grade and crest vertical curve length. Conversely, none of the bridges meet the current design standards for bridge width. The compliance of the bridges with the other geometric design standards is partial. Only one of the three bridges fully meets the guideline for the length of sag vertical curves (Deer Isle-Sedgwick Bridge); only one bridge meets the guideline for sidewalk width (Bailey Island Bridge); two bridges meet the guideline for minimum horizontal curve radius (Bailey Island Bridge and Deer Isle-Sedgwick Bridge); and two bridges meet the guideline for the inclusion of sidewalks (Bailey Island Bridge and Deer Isle-Sedgwick Bridge).

The affect that these inadequacies have on passenger safety is not fully known at this time. In order to gain a further understanding of these effects, an evaluation of safety and public opinion should be conducted. Once these deficiencies and the affect that they have on safety are identified, the feasibility of the rehabilitation project may be considered, based on project cost, time constraints, and impact to historic value (as determined by the Maine Department of Transportation). This process should be applied nationally and all state Department of Transportation offices should implement management plans for historic bridges.