Delaware Administrative Code
Title 2 - Transportation
2000 - Department of Transportation
2300 - Division of Planning and Policy
2309 - Development Coordination Manual
Chapter 5 - DESIGN ELEMENTS
Section 5.2 - SUBDIVISION AND COMMERCIAL ENTRANCE DESIGN GUIDELINES
Current through Register Vol. 28, No. 3, September 1, 2024
DelDOT has adopted policies with regard to subdivision and commercial entrances that create public intersections which warrant special consideration with respect to location and design.
A. Entrance design should consider a range of objectives that include:
B. In order to achieve the objectives mentioned above, entrances need to be properly designed with respect to:
Detailed guidance on each of the design controls mentioned above are discussed in subsequent sections of this Chapter. Figure 5.2-a illustrates the basic elements and design controls associated with entrance design. Detailed definitions for those elements described are included in the Definitions.
Figure 5.2-a Entrance and Intersection Design Elements
5.2.1 Subdivision and Commercial Entrance Design Guidelines-Process
Proper entrance design requires consideration of many design controls in the context of surrounding intersections, entrances, roadways, and their users (e.g. vehicles, pedestrians, bicycles, transit). Figure 5.2.1-a provides an outline for successfully planning and designing a commercial site entrance. It is recommended that the design engineer schedule a Pre-Submittal meeting with DelDOT staff early in the design process in order to confirm consensus on critical design controls. The design engineer assumes full responsibility for design performed without first confirming design controls with DelDOT.
Figure 5.2.1-a Subdivision and Commercial Entrance Plan Decision Flow Chart
5.2.2 Subdivision and Commercial Entrance Design Guidelines - Entrance Location
As entrances are introduced to an existing roadway, additional vehicle-to-vehicle conflict points are created, which has the direct impact of reducing safety along the roadway. Insufficient spacing between nearby entrances and intersections compound these adverse effects. While no access management program can completely eliminate safety concerns associated with entrances, there are guidelines to selecting an entrance location that can reduce these impacts.
When deciding on the location of a proposed entrance, one of the most important factors is its distance to nearby intersections. According to AASHTO, entrances should ideally be located outside the functional area of an intersection or adjacent driveway. The functional area extends both upstream and downstream from the physical intersection area and includes the longitudinal limits of auxiliary lanes. This allows for the best operations with respect to traffic exiting the site and positioning itself at the intersection approach and reduces the chance that queues from the downstream intersection will block the entrance.
Ideally, spacing between entrances should be provided as equal to the stopping sight distance on the abutting roadway. This allows drivers on the roadway to take notice and be prepared for entering or exiting vehicles at each individual access point. When spacing is shorter than this distance, the driver experiences overlapping attention demands and attention is diverted from other driving tasks.
In cases of urban infill and redevelopment, ideal spacing of entrances cannot always be provided. With that in mind, the following general guidelines should be followed when selecting an entrance location.
Figure 5.2.2-a Corner Clearance
Figure 5.2.2-b Avoiding Entrance Jog Maneuvers
Figure 5.2.2-c Desirable Offsets on Undivided Highways
(Source: Michigan Department of Transportation Traffic and Safety Note 608A)
The design elements required for a specific entrance shall be constructed within the right-of-way or easements of the roadway. The engineer is responsible for verifying the right-of-way width and that the required improvements can be constructed. If the right-of- way cannot accommodate the required entrance improvements, the developer can acquire the necessary right- of-way, restrict movements, or reduce the traffic generated from the site to eliminate the need for the improvement.
5.2.3 Subdivision and Commercial Entrance Design Guidelines - Design Vehicle
Proper entrance design with respect to safety, operations, and sustainability is heavily dependent upon selecting the appropriate design vehicle. The functional requirements associated with the entrance to a residential subdivision will be much different than those associated with the entrance of an industrial facility due to the types of vehicles that they will serve. The design vehicle has a major role in determining entrance/lane width and turning radius design. In general, Figure 5.2.3-a should be used for proper design vehicle selection based on the proposed development use. It is incumbent upon the design engineer to confirm consensus of the design vehicle with DelDOT before proceeding with design. The design engineer assumes full responsibility for designing an entrance or intersection without first confirming the selection with DelDOT.
Figure 5.2.3-a Design Vehicle Selection
*Refer to Table 2-4 of AASHTO's A Policy on Geometric Design of Highways and Streets (Green Book), 7th Edition, for additional information about design vehicle dimensions. ** Encroachment into the opposing lane of the entrance drive may be permitted but not on curb or islands. Refer to Section 5.2.5 for additional guidance.
5.2.4 Subdivision and Commercial Entrance Design Guidelines - Entrance Width
The entrance width refers to the driveway opening for both ingress and egress lanes. Proper entrance widths are dependent on the number of lanes needed to adequately serve the volume of entrance and exit movements with lanes wide enough so that movements do not encroach upon each other. Entrances should be narrow enough to provide clear points of ingress and egress with appropriate pavement and lane markings to separate movements and travel direction. Figure 5.2.4-a shows an example of poorly designed entrance widths.
Figure 5.2.4-a Poorly Designed Entrance Widths
(Source: Michigan Department of Transportation Access Management Guidebook)
In general, entrance pavement widths should be provided as shown in Figure 5.2.4-b.
Figure 5.2.4-b Entrance Pavement Widths
Notes:
It is acceptable for the entering and exit lanes to be of unequal width in order to accommodate the required turning paths of the design vehicle in combination with corner radii design, as shown in Figure 5.2.4-c.
Figure 5.2.4-c Commercial Entrance Lane Width Example
(Adopted from Florida Department of Transportation Driveway Information Guide)
When determined by a TOA or TIS, separate left and right-turn lanes may be required exiting the entrance of a commercial or large subdivision development. This may also be suggested by the engineer based on site needs. In some cases, only a small number of left-turn vehicles will cause a significant delay to right turning vehicles at a single exit lane. In this case, the additional exit lane will greatly improve operations of an entrance with high entrance volumes.
Figure 5.2.4-d Separate Left and Right-Turn Exiting Lanes
5.2.5 Subdivision and Commercial Entrance Design Guidelines - Intersection Corner Radii
The radii of an intersection's corners or the curves connecting the edges of pavement of the intersecting streets are defined by either the curb (face or where bituminous concrete/asphalt pavement and edge of gutter meet), or by the edge of pavement where there is no curb. The intersection's corner radii are key factors in the multimodal performance of the intersection. The corner radius affects the pedestrian crossing distance, the speed and travel path of turning vehicles, and the appearance of the intersection.
Excessively large pavement corner radii result in significant drawbacks in the operation of the street since pedestrian crossing distance increases with pavement corner radius. Further, the speed of turning motor vehicles making right turns is higher at corners with larger pavement corner radii. The compounded impact of these two measures-longer exposure of pedestrians to higher-speed turning vehicles-yields a significant deterioration in safety and quality of service to both pedestrians and bicyclists.
The underlying design control in establishing pavement corner radii is the need to have the design vehicle turn within the permitted degrees of encroachment into adjacent or opposing lanes. Figure 5.2.5-a illustrates degrees of lane encroachment often considered acceptable based on the intersecting roadway types. These degrees of lane encroachment vary significantly according to roadway type, and balance the operational impacts to turning vehicles against the safety of all other users of the street. Although Figure 5.2.5-a provides a starting point for planning and design, the designer must confirm the acceptable degree of lane encroachment during the project development process. It is acceptable for a design vehicle turning from a right turn lane to encroach onto the adjacent bike lane on the approach leg. Lane encroachment in full departure width (not full approach width) as shown in Condition B may be permitted at signalized intersections where a gap is provided allowing the design vehicle turning onto a multi-lane roadway to utilize both travel lanes to make a right turn. Condition C may be acceptable for right turns into an entrance if design vehicle movements are expected during off-peak times. In nearly all cases, Condition D, in which the turning vehicle encroaches into opposing flow, should be avoided. Encroachment by the design vehicle on curbed channelized islands, outer curb line or beyond the edge of pavement (when no curb is present) is not permitted.
Figure 5.2.5-a Typical Lane Encroachment by Design Vehicle
At the great majority of all intersections, whether curbed or otherwise, the pavement corner design is dictated by the right-turn movement. Left turns are seldom a critical factor in corner design, except at intersections of one-way streets, in which case their corner design is similar to that for right turns at intersections of two-way streets. The method for pavement corner design can vary as illustrated in Figure 5.2.5-b and described below.
Figure 5.2.5-b Methods for Pavement Corner Design
A simple curb radius may be used for right turns on roadways at unchannelized intersections for passenger, single unit and small semitrailer design vehicles.
In many situations, the "effective" pavement width on approach and departure legs is greater than an 11 or 12 foot wide travel lane. This is the pavement width usable, by the design motor vehicle, under the permitted degree of lane encroachment. At a minimum, effective pavement width is always the right-hand lane and therefore usually at least 11-12 feet, on both the approach and departure legs. Where a shoulder is present, the shoulder (typically 5 to 8 feet) is added to the effective width on those legs (approach, departure or both), the effective width may increase to between 16 to 20 feet. In addition, the effective width may include encroachment into adjacent lanes of traffic. An example of this is a combination vehicle using an inside travel lane to make a right turn at a signalized intersection. Figure 5.2.5.1-a shows Conditions A, B and C where the effective width may be utilized to design an intersection corner. An example using Condition B in the figure to determine the curve radius is a SU-30 vehicle turning right at a 90 degree intersection from a local road having an 11 foot travel lane and a 5 foot shoulder onto a collector road having a 12 foot travel lane and an 8 foot shoulder. Therefore, the effective approach leg width is 16 feet and the effective departure leg width is 20 feet. Figure 5.2.5.1-b provides design values for various widths of approach and departure legs at unchannelized intersections.
For larger angles of turns and/or large design vehicles, simple curve radius with taper combinations or three centered compound curves should be considered.
Figure 5.2.5.1-a Effective Pavement Width Examples
Figure 5.2.5.1-b Simple Curve Radius with Effective Widths
Minimum 15 ft. radius used.
Source: Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO Green Book, 2011, Chapter 9, Intersections
Based on values provided in Figure 5.2.5.1-b, Figure 5.2.5.1-c illustrates the components of a simple curve radius for a SU-30 design vehicle at an unchannelized intersection.
Figure 5.2.5.1-c Simple Curve Radius Example for a SU-30
The combination of a simple radius flanked by tapers can often fit the pavement edge more closely to the design vehicle than a simple radius (with no tapers). This closer fit can be important for large design vehicles where effective pavement width is small (due either to narrow pavement or need to avoid any lane encroachment), or where turning speeds greater than minimum are desired. Figure 5.2.5.2-a summarizes design elements for curve/taper combinations at unchannelized intersections that permit various design motor vehicles to turn, without any lane encroachment, from a single approach lane into a single departure lane. Values provided are for design vehicles turning from a 12 foot wide approach leg onto a 12 wide foot departure leg. If the effective width of the approach leg and/or departure leg is greater than 12 feet, than the offset or taper length ratio may be reduced to optimize the corner design. Refer to DelDOT's Intersection Corner Radii Examples which are available online at http://devcoord.deldot.gov > Guidance for additional guidance on how to design a corner with a simple curve and taper and examples.
Based on values provided in Figure 5.2.5.2-a, Figure 5.2.5.2-b illustrates the components of a simple curve radius with taper corner design for an SU-30 design vehicle at an unchannelized intersection.
Figure 5.2.5.2-a Simple Curve Radius and Taper
Source: Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO, 2011, Chapter 9, Intersections
Figure 5.2.5.2-b Simple Curve Radius and Taper Example for a SU-30
Figure 5.2.5.3-a shows the minimum edge of traveled way design values for various uses using three centered compound curves at an unchannelized intersection, without any lane encroachment, from a single approach lane into a single departure lane. Values provided are for design vehicles turning from a 12 foot wide approach leg onto a 12 wide foot departure leg. If the effective width of the approach leg and/or departure leg is greater than 12 feet, than the offset may be reduced or the radii and taper for a smaller design vehicle may be used to optimize the corner design. Refer to DelDOT's Intersection Corner Radii Examples which are available online at http://devcoord.deldot.gov > Guidance for additional guidance on how to design a corner with a three centered compound curve and examples.
Figure 5.2.5.3-a Three Centered Compound Curves
Source: Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO, 2011, Chapter 9, Intersections
Based on design values provided in Figure 5.2.5.3-a, Figure 5.2.5.3-b illustrates the components of a three-centered compound curve corner for a SU-30 design vehicle at an unchannelized intersection.
Figure 5.2.5.3-b Three Centered Compound Curves Example for a SU-30
A separate right-turn roadway, usually delineated by channelization islands and auxiliary lanes, may be appropriate where right-turn volumes are large, where lane encroachment by any motor vehicle type is unacceptable, where higher speed turns are desired, or where angle of turn is well above 90 degrees.
Three centered compound curves may be used on turning roadway for passenger vehicles and should be considered where SU and semitrailer combinations will be turning as shown in Figure 5.2.5.4-a.
Figure 5.2.5.4-a Turning Roadways and Island
Figure 7-6 Design Widths for Turning Roadways of DelDOT's Road Design Manual provides suggested simple curve radii and lane widths combinations for turning roadways based on several types of smaller design vehicle. Figure 5.2.5.4-b shows a sample turning roadway design using simple curve radii for passenger cars and occasional SU's for a right-in and right-out entrance. Figure 5.2.5.4-c shows a sample turning roadway design for bus and WB-40 design vehicles for a right-in and right-out entrance using simple curve radii. The "effective" pavement width on approach and departure legs may vary the turning roadway width and island size. In all cases, the channelizing island should be checked to verify that it meets the minimum size requirements.
Figure 5.2.5.4-b Sample Turning Roadway Design for Passenger Cars and Occasional SU-30's
Figure 5.2.5.4-c Sample Turning Roadway Design for WB-40's
Appropriate design values for turning roadways using three centered compound curves turning from a 12 foot wide approach leg onto a 12 foot wide departure leg are provided in Figure 5.2.5.4-d. When the effective width of the approach leg and/or departure leg are wider than 12 feet, then it may be possible to use smaller curve radii and offset to design the turning roadway. The turning roadway lane widths may be reduced with pavement markings to channelize passenger cars and discourage the usage of the wider turning roadway as two turning lanes. Refer to DelDOT's Intersection Corner Radii Examples which are available online at http://devcoord.deldot.gov > Guidance for additional guidance on how to design a turning roadway and examples.
Figure 5.2.5.4-d Turning Roadways
Design Classification:
A - Primarily passenger vehicles; permits occasional design single-unit trucks to turn with restricted clearances.
B - Provides adequately for the SU-30 and SU-40 design vehicles; permits occasional WB-62 design vehicles to turn with slight encroachment on adjacent traffic lanes.
C - Provides fully for the WB-62 design vehicle.
Verify island size meets minimum preferred size of 100 ft2 for curbed islands or 175 ft2 for islands with curb ramps, pedestrian refuge and pedestrian signal poles. Refer to Figures 5.2.5.5-a and 5.2.5.5-b.
The next three figures show examples of minimum turning roadway designs for 90-degree right turn based on the design vehicle and its frequency of use. Figure 5.2.5.4-e shows a minimum turning roadway using a three-centered curve with radii of 150, 50, and 150 ft with the middle curve being offset 3 ft from the tangent edged extended and a 14 ft lane width. This design not only permits passenger vehicles to turn at a speed of about 15 mph but also enables single-unit truck designs vehicles to turn on a radius (right front wheel) of approximately 65 ft and still clear turning roadway by about 1 ft on each side.
Figure 5.2.5.4-e Turning Roadway Design for Passenger Car and Occasional SU-30
By increasing the turning roadway width 2 ft and using the same combination of curves but with the middle curve being offset 7 ft from the tangent edges extended, a more desirable arrangement results as shown in Figure 5.2.5.4-f. This design enables the single unit truck design vehicles to use a 75 ft turning radius with adequate clearances and makes it possible for the WB-62 design vehicle to negotiate the turn with only slight encroachment on adjacent through-traffic lanes.
Figure 5.2.5.4-f Turning Roadway Design for SU-30 and Occasional WB-62
At locations where a significant number of semitrailer combinations, particularly the longer units, will be turning, the arrangements shown should be used as shown in Figure 5.2.5.4-g. This design, consisting of a minimum curve of 70 ft radius, an offset of 11 ft and terminal curves with radii of 200 ft generally provides for WB-62 design vehicle passing through a 25 ft turning roadway width and greatly benefits the operation of smaller vehicles.
Figure 5.2.5.4-g Turning Roadway Design for WB-62
An island's principle functions are to control and direct traffic movements, usually turning, dividing opposing and same direction traffic streams and to provide refuge for pedestrians and bicyclists. An island is a defined as an area between traffic lanes for control of vehicle movements and may be delineated by barrier curb (having a vertical rise greater than 6 inches), mountable curb (having a vertical rise 6 inches or less) or a pavement area marked by paint. P.C.C. curb, Type 2 is the preferred curb used to delineate an island. Islands should be sufficiently large to be visible to motorists and to accommodate pedestrian refuge and pedestrian signal poles where required. Figures 5.2.5.5-a and 5.2.5.5-b provide minimum and preferred island sizes as stated in Section 7.3.3 Islands of DelDOT's Road Design Manual.
Figure 5.2.5.5-a Island Sizes without Pedestrians Facilities
Figure 5.2.5.5-b Island Sizes with Pedestrians Facilities
Design Guidance Memorandum 1-22 provides additional guidance related to an island's offset from the travel lane based on several conditions. Typically, the island is offset from the traveled way the full width of the shoulder or turn lane. This offset may be reduced to only five feet to accommodate bicycles (as shown in Figure 5.2.5.5-c) under the following conditions:
As stated in the AASHTO Green Book, "islands used for channelization should not interfere with or obstruct bicycle lanes at intersections." The offset for bicycles may be reduced to 4 feet at locations of high pedestrian use to minimize crossing time.
If U-turn movements are permitted on the intersecting roadway where channelizing islands are proposed to extend into the shoulder, then U-turn turning movement diagrams shall be prepared and submitted for review to verify that U-turn movements may still be made or to determine if additional signing or movement restrictions are needed for certain design vehicles.
Figure 5.2.5.5-c Triangular Island Offsets
For every island configuration, positive drainage must be provided for the safety of vehicles and pedestrians. The corners of the island shall be flush with the pavement as per the Standard Specifications for snow plowing operations. The corners of islands which are not offset the full width of the shoulder adjacent to the roadway shall be delineated with flexible delineators as per the Standard Specifications Section 701.11. See Chapter 7 Intersections of the Road Design Manual for additional information.
Prior to finalizing the island design, the engineer shall verify that the minimum island size listed in Figures 5.2.5.5-a and 5.2.5.5-b have been met. If the island size is not met using the recommended three centered compound curve radii from Figure 5.2.5.4-d, then the curve radii and/or offsets should be increased until the required minimum island size is achieved.
Based on the design vehicle chosen for the proposed development, turning movement diagrams shall be included with the initial plan submittal to verify that the minimum requirements for edges of traveled way for the design vehicle, drive aisle widths and channelizing islands sizes are met. Proposed pavement markings and an elevation view of the design vehicle must be shown on the diagrams. If u-turn movements will be permitted at intersections, then include the turning movements on the diagrams. If a signal is proposed at the intersection, then electronic files shall be forwarded to the Traffic Section to begin signal design only after these design features have been verified.
The design vehicle shall be properly positioned within the traffic lane at the beginning and end of the turn with a 2 foot offset from the edge of traveled way on the tangents. It is recommended to maintain the 2 foot offset of the design vehicle's inner wheel path throughout most of the turn and with a clearance at no point less than 9 inches from the face of curb or edge of pavement if uncurbed as shown in Figure 5.2.5.6-a. If a turning software application is used to create the templates, a minimum 10 mph speed shall be used for the design vehicle.
Figure 5.2.5.6-a Turning Movement Offsets
5.2.6 Subdivision and Commercial Entrance Design Guidelines - Entrance Length
The entrance length refers to the amount of space available for stacking incoming and outgoing vehicles or the distance between the street and the end of the entrance within the development. As shown in Figure 5.2.6-a, when insufficient lengths between the entry point and parking spaces or on-site drive aisles exist, vehicles can be subject to multiple conflict points near the entrance which inhibit operations on the adjacent roadway as well as within the developed site. Figure 5.2.5-b shows recommended minimum entrance lengths based on proposed land uses.
If the use of an entrance is to be controlled by an electronic gating system, the gate shall be located a minimum of 50 feet from the edge of the shoulder, and a turnaround for the appropriate design vehicle must be provided within the site entrance, in the area between the Right-Of-Way and the gates. For proposed uses that would be anticipated to create a queue of vehicles waiting to pass through the gating system, additional storage length may be required between the Right-Of-Way and the gates.
Figure 5.2.6-a Entrance Length Example
Source: Michigan Department of Transportation Access Management Guidebook
Figure 5.2.6-b Recommended Minimum Entrance Lengths
Note: For large developments 100,000 s.f. or greater, the total recommended length is not necessary for all entrances, only the major ones.
Considerations for entrance length are especially important when the proposed use includes an element of drive-thru service such as fast-food restaurants, banks, and pharmacies. It is important that sufficient length be provided to allow the queuing of vehicles at drive-thru windows to be contained within the site and not back up into lanes of the adjacent roadway. Figure 5.2.5-c provides recommended queue distances for design consideration based on land use and the expected maximum number of queued vehicles.
Figure 5.2.6-c Recommended Drive-thru Queue Distances
Notes:
5.2.7 Subdivision and Commercial Entrance Design Guidelines - Horizontal Alignment
Horizontal alignment of two-way entrance drives should be designed to intersect the frontage road at 90° whenever possible. Skewed intersections can reduce visibility of approaching motor vehicles, require higher degrees of traffic control, require more pavement to facilitate turning vehicles, and require greater crossing distances for pedestrians. If this is not possible due to field conditions, then the intersection angle must always be greater than 70°.
One-way commercial entrance drives may be used having a range of 60° to 90° without interfering with the motorists' visibility as shown on Figure 5.2.7-a.
Figure 5.2.7-a Angle of Driveway
5.2.8 Subdivision and Commercial Entrance Design Guidelines - Vertical Alignment
Vertical alignment of entrances with the adjacent roadway is an important design consideration. Vehicles must slow down to traverse abrupt changes in grade, creating increased speed differentials with the adjacent roadway which increases crash potential. Another concern is the visibility of the entrance. For example, an entrance that slopes down and connects with a roadway on a superelevated horizontal curve can create issues with sight distance (see Figure 5.2.8-a).
Figure 5.2.8-a Vertical Alignment at an Entrance
(Source: Florida Department of Transportation Driveway Information Guide)
Profiles of entrances shall be designed to include vertical curves at their intersections with adjacent roadways using the design criteria shown in Figure 5.2.8-b. Vertical curve transition shall be provided at the intersection of the entrance profile and the cross slope of the roadway shoulder extended. Transition lengths should be based on minimum K-values listed in Figure 5.1.2-a. Minimum grades should be 0.5% and maximum grades should not exceed 8% for commercial entrances and 10% for residential entrances. Special design consideration must also be given to locations where pedestrian crossing facilities are proposed at entrances. All sidewalk, curb ramp, and crosswalk longitudinal slopes and cross slopes must adhere to applicable regulations and should follow DelDOT guidance for achieving Americans with Disabilities Act (ADA) compliance.
Figure 5.2.8-b Entrance Drive Tie-in to Frontage Road
(Source: Florida Department of Transportation Driveway Information Guide)
5.2.9 Subdivision and Commercial Entrance Design Guidelines - Auxiliary Lanes
When turning movements are introduced to a roadway, speed differentials between turning vehicles and through traffic are created. These differentials have a detrimental effect on both crash potential and level of service. Auxiliary lanes provide an area for turning traffic to be separated from the through lanes in an effort to improve safety and capacity of the roadway. Auxiliary lanes include right-turn lanes, left-turn lanes, bypass lanes, and crossovers. Auxiliary lane length should be dictated by traffic volumes, composition, speeds, desired level-of-service, and local conditions. Auxiliary lane warrants and lane lengths shall be determined in accordance with this section. Projects shall demonstrate compliance by completing DelDOT's Auxiliary Lane Worksheet available in the "Doing Business" section of DelDOT's website available online. Projected 10-year roadway ADT shall be calculated by multiplying the roadway AADT by the "10-Year Growth Factor" (which is established as 1.16 based on assumed 1.5% annual growth in the Auxiliary Lane Worksheet or provided by DelDOT if a TOA/TIS is performed) and multiplied by the associated K and D factors from the latest DelDOT Traffic Summary Report, (published on the DelDOT website annually under "Vehicle Volume Summary (Traffic Counts)" at: https://deldot.gov/Publications/manuals/traffic_counts/index.shtml and then adding any known committed development and site approach traffic volumes. If traffic counts are collected or a TOA/TIS is performed, those traffic volumes can be utilized instead of applying the associated K and D factors. Projected 10-year roadway ADT shall be used for the analysis. The "Traffic Generation Input Tab-1" and "Aux Lane Inputs - Tab 2" on the Auxiliary Lane Worksheet shall be completed and submitted for review for each proposed entrance. If the entrance is to be signalized, the "Signalized Intersection-Tab 7" tab shall also be completed and submitted for review for each proposed entrance.
Right-turns can be free flowing, yield or stop-controlled. In order to operate properly, free flowing right-turn lanes must have an adequate deceleration distance, with no access points, for drivers to safely merge with and diverge from the through traffic. Separate right-turn lanes at signalized and unsignalized intersections shall be required when warranted in accordance with this section. Projects shall demonstrate compliance by completing DelDOT's Auxiliary Lane Worksheet. Right-turn lanes shall be designed in accordance with Figure 5.2.9.1-a and b. A five foot bike lane shall be provided between the adjacent travel lane and right-turn lane to accommodate bicycles. Listed below are notes related to the warrants and right turn lane lengths:
Figure 5.2.9.1-a Right Turn Lane Warrants (R<50')
Assumptions
Figure 5.2.9.1-b Right Turn Lane Warrants (R>50')
Assumptions
A bypass lane is a paved shoulder that permits through traffic to bypass a left-turning vehicle which is stopped on the travel lane. They are intended to reduce delay and expedite the movement of through traffic at T- intersections.
An intersection shall first be considered for a bypass lane using the warrants in accordance with Figure 5.2.9.2-a of this section. Projects shall demonstrate compliance by completing DelDOT's Auxiliary Lane Worksheet. Bypass lanes shall be designed in accordance with Figure 5.2.9.2-b. A five foot shoulder shall be provided on the outside of the bypass lane to accommodate bicycles.
Listed below are notes related to the warrants and bypass lane lengths:
Figure 5.2.9.2-a Bypass Lane Warrants
*See Section 5.2.9.2.D and Section 5.2.9.3.J for special cases with very low opposing volumes
|
Posted Speed (mph) |
Approach Taper Length (feet) |
|
25 |
Bypass Lane Not Warranted |
|
30 |
125 |
|
35 |
155 |
|
40 |
155 |
|
45 |
180 |
|
50 |
215 |
|
55 |
250 |
|
Posted Speed (mph) |
Departure Taper Length (feet) |
|
25 |
Bypass Lane Not Warranted |
|
30 |
65 |
|
35 |
80 |
|
40 |
80 |
|
45 |
90 |
|
50 |
110 |
|
55 |
125 |
Notes:
Assumptions:
Figure 5.2.9.2-b Typical Entrance Diagram with Bypass Lane
Separate left-turn lanes shall be required on signalized and unsignalized intersections of roadways when warranted. If left turns are proposed on roads with an Arterial classification, or roads with 2 or more travel lanes that must be crossed, the project shall be referred to DelDOT prior to start of site design for an access determination, in accordance with applicable sections such as 1.5.2 Arterials - Design Standards or 1.2.1 Entrance Policy - Location of Entrances, prior to allowing the left turning movement or designing an auxiliary lane, (such as a left-turn lane, a two way left turn lane or other traffic storage facility). When it is determined that a project shall generate sufficient number of left-turns to warrant the construction of an auxiliary lane to accommodate left-turns, it shall be the responsibility of the developer to construct an auxiliary lane, (such as a left-turn lane or other traffic storage facility as directed by DelDOT), at the locations designated by DelDOT. Left turn lanes when permitted shall be designed in accordance with Figure 5.2.9.3-b. Raised medians should be considered and designed in accordance with applicable guidelines and standards such as: Chapters 4 and 9 of AASHTO's Policy on Geometric Design of Highways and Streets (The Green Book) or other NAS.
A separate left-turn lane shall be required for all signalized entrances located on roadways. The design shall be in accordance with applicable standards and guidelines such as the Highway Capacity Manual (HCM) or NAS. When access to a proposed site requires vehicles to utilize an existing left-turn lane, the existing facility shall be evaluated for compliance with the requirements of this section, and the appropriate configuration shall be demonstrated using the Auxiliary Lane Worksheet, to determine if modifications are needed to provide sufficient storage length. The developer will be required to make any modifications necessary to provide an adequate left- turn lane.
Listed below are notes related to the warrants and left turn lane lengths:
Figure 5.2.9.3-a Left-Turn Lane Warrants at Unsignalized Intersections
Assumptions
|
Deceleration Length (ft) = Brake Reaction (ft) + Braking on Level (ft) |
Posted Speed (mph) |
|||||
|
25 |
35 |
40 |
45 |
50 |
55 |
|
|
Brake reaction distance |
44.1 |
58.8 |
58.8 |
66.2 |
73.5 |
80.9 |
|
Braking distance on level |
86.4 |
117.6 |
117.6 |
153.6 |
194.4 |
240 |
|
Stopping Sight Distance |
131 |
177 |
177 |
220 |
268 |
321 |
Figure 5.2.9.3-b Typical Entrance Diagram with Left-Turn Lane
Crossover design at two-lane crossroads or connecting roads should be in accordance with standard crossover design found in applicable guidelines, standards and manuals such as: Chapter 9 of AASHTO's Policy on Geometric Design of Highways and Streets (The Green Book) and DelDOT's RDM or other NAS.
The following general guidelines shall be used:
Figures 5.2.9.4-a thru 5.2.9.4-d provide examples for directional median crossovers providing left-in movements for WB-40 and WB-62 design vehicles and U-turn movements for passenger car vehicles from a divided roadway with varying median widths being measured from the median nose.
Figure 5.2.9.4-a Directional Median Crossover for WB-40 D.V. - Median Width >=4' to < 18'
Figure 5.2.9.4-b Directional Median Crossover for WB-62 D.V. - Median Width >=4' to < 18'
Figure 5.2.9.4-c Directional Median Crossover for WB-40 D.V. - Median Width >=18'
Figure 5.2.9.4-d Directional Median Crossover for WB-62 D.V. - Median Width >=18'
5.2.10 Subdivision and Commercial Entrance Design Guidelines - Bike Lanes
Suitable accommodations for bicyclists shall be required for all subdivision and commercial site plans. Additional guidance is available through DelDOT's Complete Streets Policy and other reference materials. All new roadways, except those where bicyclists shall be legally prohibited, shall be designed and constructed to encourage use of bicycles as a form of transportation. Unless access is specifically denied, some level of bicycle use can be anticipated on most roadways. Site entrance designs must accommodate bicycle traffic.
The design of a bike lane needs to include appropriate pavement markings and signing approaching and through intersections to reduce the number of conflicts. Guidance for signing and pavement marking of bike lanes is provided through regulations and standards such as the DE MUTCD and AASHTO's Guide for the Development of Bicycle Facilities.
A bike lane shall be delineated to indicate the separation from the motor vehicle travel lanes with a five-inch wide solid white line. Adequate pavement surface, bicycle-safe grate inlets, and safe railroad crossing shall be provided on roadways where bicycle lanes are being designated. Raised pavement markings and raised barriers can cause steering difficulties for bicyclists and shall not be used to delineate bicycle lanes.
