2 Del. Admin. Code § 5.5
Typical sections shall be designed in accordance with the requirements of this section, and shall include all necessary features as specified in Chapter 4.
Curbing may be used to accommodate stormwater runoff. Refer to the DelDOT Standard Construction Details for curb types. Any proposed modification to the DelDOT standard curb types shall be shown with a detail on the construction plan and is subject to DelDOT approval.
A minimum of six inches of GABC type B shall be placed under curbs proposed in subdivisions and four inches for all curbs proposed elsewhere and shall extend six inches beyond the back of curb.
Curbs shall be used for all entrances and islands located in the following areas:
The type of curb to be used must be shown on the entrance drawing. Where the roadway is curbed, any curb returns of the driveway shall match the existing curb line. In rural areas curbing may be omitted if access and drainage can be effectively controlled by a roadside ditch or other means as determined by DelDOT.
No portable curb channelization shall be permitted on the entrance facility. Curbing for channelization should be constructed using a mountable-type curbing having a sloping face such as type 2 PCC curb. Special details must be included in the construction plans. Channelization may be poured monolithically if approved by DelDOT.
If drainage runoff will be conveyed along the edge of a curbed frontage road, then a curb and gutter type shall be used. Curbs proposed on roadways with a design speed of 50 mph or greater shall be mountable and be limited to a 4 inch vertical face. Roadways with a design speed of 45 mph or less should use an 8 inch barrier curb.
Where 8 inch height curb is allowable, it must include a throat adjacent to drainage inlets. Refer to Section 5.7 for more information.
Where guardrail is proposed, a maximum curb height of 4" is allowed and shall be positioned under the w-beam railing as shown on standard detail no. B-1. Within the limits of the end treatment and throughout the length of the taper grading, a maximum curb height of 2" is allowed as shown on standard detail no. B-2.
Figure 5.5.2-a Subdivision Street Typical Section (With Curb) - Types I and II
(Not to Scale)
Figure 5.5.2-b Subdivision Street Typical Section (With Curb) - Type III
(Not to Scale)
Figure 5.5.2-c Subdivision Street Typical Section (Without Curb)
(Not to Scale)
Figure 5.5.2-d Industrial Streets Typical Section (With and Without Curb)
(Not to Scale)
The minimum depth of a ditch has been established to provide for sub-surface drainage. This minimum depth must be maintained throughout the subdivision. This depth can vary if a swale over a closed drainage system is used.
To minimize rutting and erosion of the roadside due to on-street parking, the site plan shall be developed to allow for vehicles to be stored in the driveway beyond the right-of-way. A note on the record plan shall state this requirement.
A six-foot grass shoulder shall be treated with an approved turf reinforcement mat to protect the edge of the pavement and to minimize the potential for soil erosion. In addition, design stormwater velocities within the open ditch section should be limited to a maximum of three feet per second.
If pipes are used at site entrances in conjunction with an open drainage system, the longitudinal slope from the entrance pavement to the top of the pipe shall be six-to-one (6:1).
The long-term presence of water within the pavement structure is largely responsible, directly and indirectly, for many of the distress and performance problems in pavement systems. The addition of longitudinal perforated underdrains is a feasible and cost-effective option for removing water from the road bed. Underdrains are a system of perforated pipes that collect and transmit the water to an outfall site.
Underdrains shall be installed at a minimum length of 150' in each direction from any sump location on all subdivision streets. Based on field conditions encountered while performing reviews or during construction, additional underdrain may need to be installed, at DelDOT's direction, along portions of streets affected by conditions such as the following: segments that have a longitudinal slope of 2% or flatter, where high water-table issues are observed, where the road is placed in a deep-cut versus original existing grade, or where poor soils are present. The typical section shall show the location of the underdrain in accordance with Figures 5.5.1-a through 5.5.1-d. Refer to DelDOT's Standard Construction Details for dimensions and materials.
If the developer can demonstrate underdrains are not warranted, through an engineering analysis, signed and sealed by a Professional Engineer registered in Delaware, DelDOT shall grant a waiver on the required underdrains referenced above. All costs associated with the developer's engineering analysis shall be at their cost. DelDOT will not provide any reimbursement.
The engineering analysis shall include the following:
Upon submission of all the information listed above, DelDOT will review the analysis and provide a written response to the developer's request for non-utilization of underdrains.
The clear zone as defined in AASHTO's Roadside Design Guide (RDG) includes "the total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles. This area may consist of a shoulder, a recoverable slope, a non-recoverable slope, and/or a clear run-out area. The desired width is dependent upon the traffic volumes and speeds and on the roadside geometry."
Adequate lateral clearance between the edges of traffic lanes and roadside obstructions has been shown to be a very important safety factor. Vehicles leaving the roadway should have a reasonable opportunity to recover control and return to the roadway without overturning or colliding with roadside obstacles such as trees, poles, headwalls, or other large objects. The combination of a relatively flat slope and an obstacle-free roadside within the prescribed clear zone helps this situation.
The determination of a clear zone is a function of speed, volume, curvature, and embankment slope. Chapter 3 of AASHTO's RDG or other NAS should be used for determining clear zone widths. When deviations from the clear zone criteria are proposed, the engineer shall prepare and submit justification for review and approval by the Subdivision Engineer. Justification documentation may include but not be limited to: tables and excerpts from Chapter 3 of AASHTO's RDG or other NAS; construction plan views; and typical sections of the area. Regardless of the required clear zone width or ability to implement that width fully, a minimum horizontal clearance of 10 feet from the edge of travel lane and 5 feet from the edge of pavement shall be provided along rural collectors and rural local roads.
Some roadside appurtenances, such as guardrails, breakaway light poles and signs using breakaway posts, may be part of a proposed development. If they are located within the specified clear zone they must be crashworthy in accordance with applicable guidelines and standards such as: NCHRP Report 350 Test Level III Criteria, AASHTO's Manual for Assessing Safety Hardware (MASH) or NAS. When used, they should also be placed in the safest available location.
For guardrails within the clear zone, it is desirable to maintain a minimum 2 foot lateral offset between the outer edge of the usable shoulder and the face of the rail. Guardrails in and of themselves present a hazard and only should be used as a last resort if objects cannot be moved or the required sideslopes cannot be provided. At bridge approaches, guardrails should either match the width of the bridge or taper to meet the bridge rail. Refer to DelDOT's Standard Construction Details for more information on guardrail types and end treatments.
For arterials and other non-controlled access facilities in an urban environment, however, rights-of-way often are extremely limited and, in many cases, establishing a clear zone using guidance in Chapter 3 of DelDOT's RDM is not practical. These urban environments are characterized by sidewalks beginning at the back of curb, enclosed drainage, numerous fixed objects (ex: signs, utility poles, fire hydrants, etc.) and frequent traffic stops. These environments typically have lower operating speeds and, in many instances, on-street parking. In these environments, a lateral offset to vertical obstructions, including breakaway devices, may be used to accommodate motorists operating on the highway.
The lateral offset value of 1.5 ft. has been considered a minimum lateral distance for placing the edge of objects from the face of curb. The minimum lateral offset was never intended to represent an acceptable safety design criteria, though sometimes it has been misinterpreted as such. In a constrained urban environment, there is still a need to position rigid objects as far away from the active traveled way as possible.
A few general guidelines have been provided below for lateral offsets, but, chapter 10, Roadside Safety in Urban or Restricted Environments, of the 2011 AASHTO RDG discusses in detail the various applications for lateral offsets. Please refer to applicable guidelines and standards such as those found in AASHTO's RDG to help determine the appropriate lateral offset(s) for your site-specific location.
Figure 5.5.6-a Lateral Offset Widths
Figure 5.5.6-b Lateral Offsets at Merge Points
Figure 5.5.6-c Lateral Offsets at Entrances
2 Del. Admin. Code § 5.5
15 DE Reg. 551 (10/01/11)
16 DE Reg. 1199 (5/1/2013)
18 DE Reg. 240 (9/1/2014)
18 DE Reg. 709 (3/1/2015)
19 DE Reg. 73 (7/1/2015)
19 DE Reg. 938 (4/1/2016)
23 DE Reg. 378 (11/1/2019) (Final)