101 - Introduction
101.1 Purpose
- Structure design practices specific to the State of Delaware;
- Delaware preferences and interpretation of American Association of State Highway and Transportation Officials (AASHTO) specifications necessary to provide consistent structure designs; and
- The minimum criteria and information necessary to produce documents for the fair procurement of construction services.
101.2 Limitations of the Design Manual
101.3 Policy
101.4 Applicable Design Specifications and Standards
101.4.1 Design Specification Reference Nomenclature
References to AASHTO commentary carry the prefix AC.
References to the sections within this Manual carry no prefix.
References to commentary to sections within this Manual carry the prefix C.101.4.2 Design Specifications
- AASHTO LRFD Bridge Design Specifications, 2017, 8th Edition
- AASHTO/American Welding Society (AWS) D1.5M/D1.5:2015 – Bridge Welding Code, 7th Edition including interims through 2019
- AASHTO Manual for Bridge Evaluation, 3rd Edition, 2018
- AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, 1st Edition, 2015, including interims through 2020
101.4.3 AASHTO Interim Specifications and New Editions
101.4.4 Deviations from Specifications
101.4.5 Order of Precedence
101.4.6 Modifications to the Design Manual
101.4.7 Additional Reference Manuals and Documents
DelDOT references, along with additional materials pertinent to project development, can be found on the DRC portion of DelDOT’s website and are referred to as follows in this Manual:
- DelDOT Project Development Manual (PDM)
- DelDOT Road Design Manual
- DelDOT Quality Assurance/Quality Control Plan
- DelDOT CADD Standards Manual (Wiki Format)
- DelDOT Standard Specifications for Road and Bridge Construction (Standard Specifications)
- DelDOT Standard Construction Details
- DelDOT Pedestrian Accessibility Standards for Facilities in the Public Right of Way
101.5 Terms
The 13 Controlling Design Elements are:
- Design Speed
- Through lane and auxiliary lane widths
- Shoulder widths
- Stopping sight distance on vertical and horizontal curves
- Horizontal alignment (radius of curves)
- Vertical Alignment
- Minimum and maximum grades
- Cross slopes
- Superelevation rate
- Horizontal clearance
- Vertical clearance
- Bridge width
- Structural capacity
Additional information related to design exceptions and the justification of design exceptions is found in the Road Design Manual, Chapter 3.1.3, Departure From Standards.
Design Resource Center (DRC) – the DRC is a page on DelDOT’s website that contains a variety of data related to the development of transportation projects in the State. The DRC can be located at: http://www.deldot.gov/Business/drc/index.shtml.
Design Variance – a request to deviate from the Department’s governing standards excluding the 13 Controlling Design Elements, which may be warranted by special or unique project conditions.101.5.1 Bridge Types
Bridge – In Delaware, a bridge is defined as a structure, including supports, erected over a depression or an obstruction, such as water, a road, or a railroad, for carrying traffic or other moving loads that has an opening exceeding 20 square feet. Bridges with a clear span greater than 20 feet are included on the National Bridge Inventory (NBI).
Major bridges – Major bridges are defined as bridges with an estimated construction cost of $40 million or more. This criterion also applies to individual units of separated or dual bridges.
Complex bridges – Complex bridges are curved girder bridges, moveable bridges, stayed girder bridges, segmental bridges, and any structure having a clear unsupported length in excess of 350 feet, or bridges classified as complex by the Bridge Design Engineer on the basis of type, size, and location (TS&L) or conceptual review. Complex bridges also include those with difficult or unusual foundation problems, new or complex designs involving unusual structures or operational features, or bridges for which the design standards or criteria may not be applicable. Use of new products and experimental or demonstration projects are also considered as unusual structures.101.5.2 Roadway Types
101.5.2.1 Functional Classification
- Rural System
- Principal Arterial – Interstate
- Principal Arterial – Other
- Minor Arterial
- Major Collector
- Minor Collector
- Local
- Urban System
- Interstate
- Freeways and Expressways
- Principal Arterial
- Minor Arterial
- Major Collector
- Local
101.5.2.2 National Highway System
101.5.3 Project Types
Intermediate Projects – Intermediate project types consist of bridge rehabilitation projects and/or bridge superstructure replacement projects.
Preventative Maintenance – Preventative maintenance projects include rehabilitation or restoration of specific elements of a bridge when such activities are a cost-effective means of extending bridge service life. The majority of the work for these projects is usually maintained between the existing curb lines or outer edges of the shoulders. Preventive maintenance activities include, but are not limited to, bridge painting, deck rehabilitation, joint replacement or repair, bearing replacement, installation of pile jackets, placement of scour countermeasures, and seismic retrofit.101.6 FHWA Stewardship and Oversight Agreement
DelDOT may assume FHWA’s Title 23 responsibilities for design; plans, specifications, and estimate (PS&E); contract awards; and inspections, with respect to Federal-aid projects on the NHS if both DelDOT and FHWA determine that assumption of responsibilities is appropriate.
FHWA may, in its discretion and on a case-by-case basis, retain any specific approval or related activity for any project located on the NHS. Those projects for which FHWA retains certain project-specific actions or related responsibilities will be identified as Projects of Division Interest (PoDIs). Project approvals and related activities retained by FHWA will be identified in individual project oversight plans. FHWA, in coordination with DelDOT, will use a risk-based approach to determine which NHS projects are considered PoDI and which project areas warrant FHWA approval or oversight. An updated PoDI list will be maintained in a manner that is easily accessible and readily available to both FHWA and DelDOT project staff. Criteria for identifying PoDI projects are further outlined in Section IX of the S&O Agreement.
DelDOT may assume FHWA’s Title 23 responsibilities for design, PS&Es, contract awards, and inspections, with respect to Federal-aid projects off the NHS (non-NHS) unless DelDOT determines that assumption of responsibilities is not appropriate (Title 23 the United States Code [U.S.C.] 106(c)(2)). Project approvals and related activities for which DelDOT has assumed responsibilities are outlined in Attachment A of the S&O Agreement.
DelDOT assumption of responsibilities under 23 U.S.C. 106(c) covers six areas: design; PS&E; contract awards; and inspections, which are defined more specifically in Section VI of the S&O Agreement.
Any approval or related responsibility not listed in Attachment A cannot be assumed by the State without prior concurrence by FHWA. A list of the most frequently occurring approvals and related responsibilities that may not be assumed by DelDOT are listed in Section VII of the S&O Agreement.
For projects that have FHWA oversight, Section XI outlines the criteria that FHWA must follow. For DelDOT administered projects, DelDOT is responsible for demonstrating to FHWA how it is carrying out its responsibilities in accordance with the S&O Agreement. DelDOT oversight and reporting requirements are outlined in Section XII of the S&O Agreement.
All Federal-aid projects on the NHS should be reviewed with the Bridge Design Engineer at initiation to determine the level of FHWA involvement.101.7 Computer Software
101.8 Feedback
101.9 References
AASHTO, 2015. AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, 1st Edition.
AASHTO, 2017. AASHTO LRFD Bridge Design Specifications, 8th Edition.
DelDOT, n.d. Standard Construction Details.
DelDOT, 2020. Standard Specifications for Road and Bridge Construction, August.
DelDOT, 2009. Quality Assurance/Quality Control Plan, January.
DelDOT, n.d. CADD Standards Manual, (Wiki Format).
DelDOT, 2015. Project Development Manual, July.
DelDOT, 2004. Road Design Manual, January, with Interim Revisions.
FHWA, 2013. Traffic Monitoring Guide, Office of Highway Policy Information, September.