This chapter identifies the site access improvements required to support proposed entrances and street connections. The function, applications, and geometric design of various site access improvements, including frontage improvements and turning lanes, are discussed in this chapter. The site access improvements required for different types of development projects, highway functions, and traffic conditions are specified. Some projects may be eligible for exceptions as discussed in 4.11 Exceptions and Special Cases.
4.1.2 Scope of Improvements – The scope of improvements required by MDOT SHA to support the proposed access generally reflects the type and size of the development, the number and location of proposed access points, the anticipated traffic conditions, and the functional requirements, operational characteristics, and geometric conditions of the state highway. The State Highway System designation, highway functional classification, prevailing approach speeds, traffic volumes, driver expectancy, sight distance, adjacent access points, nearby intersections, existing lane markings, and other existing and anticipated geometric conditions on the highway are considered during the review process.
4.1.3 Frontage Channelization – Frontage channelization and related highway improvements may be required for any project, in accordance with 4.3 Deceleration Lanes. The construction of barrier curb and gutter along the frontage of developing properties is necessary to delineate the means of vehicular ingress and egress to roadside development. This confines vehicular movements to the permitted entrances, provides an appropriate roadside condition for lower speed highways in urbanized areas, and affords protection for pedestrians on adjacent sidewalk. Along higher speed highways, roadside grading using relatively flat slopes provides an appropriate treatment for the safety of errant vehicles. Curb and gutter may be reduced or eliminated in many rural applications where appropriate roadside grading is feasible.
In any development setting, the necessary highway improvements may include roadside grading, storm drainage, traffic control measures, utility relocation, and adjustment of various highway features. MDOT SHA may require the design of frontage improvements to be coordinated with long-term highway plans, local master plans, or other construction projects, thereby reducing or minimizing future impacts, costs, and traffic disruption.
4.1.4 Turning Lanes – Turning lanes typically include deceleration lanes, acceleration lanes, bypass lanes, and left-turn lanes. They may be required in accordance with 4.4 Acceleration Lanes to address right and left turns both in and out of an access point. Turning lanes are an important element of site access improvements in that they allow speed changes and turning maneuvers to occur outside of the normal flow of highway traffic. This reduces the incidence of rear-end collisions at the access point and helps to maintain through-traffic flow on the highway. Accordingly, MDOT SHA requires turning lanes for public road connections and for commercial sites that will generate appreciable traffic during times of peak travel on the state highway.
4.1.5 Improved Shoulders – Where formal turning lanes are not expressly required by this policy, widening to provide an improved shoulder may be required for any access point to address occasional turning vehicles, in accordance with 4.7 Other Auxiliary Lanes. This includes providing new shoulders, widening along existing shoulders, and reconstructing existing shoulders to provide a traffic bearing surface outside of the normal travel lanes of the highway to address occasional turning movements.
4.1.6 Limits of Improvements – The existing highway shall be widened as necessary to support the required frontage channelization, turning lanes, and improved shoulders and provide appropriately-designed transitions between improved and unimproved segments of the highway. Applicants are advised that the required widening may extend beyond the developing property frontage. For this reason, the availability of sufficient right-of-way to construct acceptable turning lanes must be considered when determining the location of proposed access. If sufficient right-of-way is not available, MDOT SHA may require the applicant to use a different access point location where the normally-required features are feasible.
4.1.7 Prior Improvements – Improvements proposed for a new project shall not adversely affect, diminish, or otherwise compromise the effect of improvements previously constructed for another project, unless specifically authorized by MDOT SHA. For example, previously-built acceleration and deceleration lanes that serve an existing development may not be eliminated to accommodate a left turn lane into a new development on the opposite side of the highway.
4.2.2 Exceptions – Channelization may be waived in the following instances, unless a safety issue results:
Table 4.2.1 Standard Frontage Channelization
Deceleration lanes reduce the risk of rear-end collisions by allowing speed reduction and right turns to take place outside of the highway through-lanes. Depending on their length, either full or partial speed adjustment can occur within the deceleration lane, thereby reducing speed differentials and associated traffic disruption in the through-lanes. The importance of providing for complete speed adjustment is increased with greater right-turning and/or approach volumes and higher operating speed. In addition, the function of the highway must be considered. For example, full-speed change lanes may be appropriately required for any access along controlled-access highways and highly-traveled arterial routes in order to minimize adverse effects on their capacity and service conditions. In contrast, an improved shoulder may be acceptable, in lieu of a formal deceleration lane, for relatively minor development along low-speed routes that provide a collector function.
Table 4.3.2 Deceleration Lane Warrants
4.3.3 Length Required – The length of Standard Full Deceleration Lanes and Standard Partial Deceleration Lanes will be as discussed below.
Table 4.3.3.A Length Required for Full Deceleration Lanes
4.3.3.B. Standard Partial Deceleration Lanes – The layout of Standard Partial Deceleration Lanes is as follows:
Table 4.3.3.B Length Required for Partial Deceleration Lanes
4.4.2 Warrants – Acceleration lanes may be required for any access point deemed necessary by MDOT SHA to provide acceptable safety and traffic operations on the state highway. In the absence of compelling site-specific considerations, acceleration lanes are required in accordance with the criteria given in Table 4.4.2.
Table 4.4.2 Acceleration Lane Warrants
4.4.3 Length Required
Table 4.4.3.B Length Required for Partial Acceleration Lanes
As the volume of opposing traffic and/or left-turning vehicles increases, queuing of vehicles waiting to execute left turns is more likely to occur. Left-turn lanes substantially improve the safety and operation of intersections and median crossovers on multilane highways. Their design combines the function and benefits of deceleration lanes with storage capacity for queuing of vehicles waiting to make left turns. Left-turn lanes allow speed reduction and queue storage to take place outside of the normal travel lanes, thereby reducing the likelihood of rear-end collisions and reducing the disruption of through-traffic.
Bypass lanes are often employed on two-lane undivided highways to accommodate occasional left-turning vehicles at “T” intersections without affecting the location of existing through-lanes. The bypass lane allows through-traffic to maintain travel at the posted speed while passing to the right of a vehicle stopped in the normal travel lane waiting to execute a left turn. Where frequent queuing of left turning vehicles may be expected on two-lane highways, a dedicated left-turn lane may be necessary instead of a bypass lane. Larger commercial sites and subdivisions, particularly those on higher volume routes, will typically require a dedicated left-turn lane as opposed to a bypass lane. In general, left-turn lanes are appropriately provided when a 4th leg is introduced to an existing “T” intersection.
In the absence of compelling site-specific considerations, bypass lanes or left-turn lanes are required in accordance with the criteria given in Table 4.5.2:
Table 4.5.2 Left Turn/Bypass Lane Warrants
4.5.3 Geometric Layout for Left Turn Lanes
The required deceleration length varies according to the posted speed and functional classification of the highway. This yields the following standards to be applied:
4.5.3.C. Storage Length – The required storage length shall always be consistent with the results of an approved traffic study. Storage length shall be determined from an appropriately-supported queuing analysis. For passenger vehicles with arrival times distributed throughout the peak hour, the following formula may be used as a guide:
Queue Storage Length Required = 1.25 X (# of peak hour left turns)
Where a storage length less than 50’ is indicated, the left-turn lane lengths given in Table 4.5.3 Left Turn Bay Lengths above will be considered sufficient to address queue storage.
Additional storage length may be required to address school bus, truck, or other commercial vehicle traffic characteristics, as determined by MDOT SHA.
The lane shift taper is a separate requirement, not to be confused with the left-turn bay taper discussed in 4.5.3.B.
Table 4.5.4 Standard Lengths for Bypass Lanes
4.5.4.B. Urban Areas – In urban areas, the approach taper may be reduced to 100' with the difference applied to increase the approach lane length.
Shoulder improvement is defined as the construction of new shoulders, or widening and reconstruction and/or resurfacing of existing shoulders, to provide a traffic-bearing paved area outside of the normal travel lanes for accommodating turning movements at the proposed site access.
4.6.2 Length Required – The length required for a shoulder improvement varies with the intended use, as follows:
Requirements with respect to the construction or modification of other auxiliary use lanes, such as two-way center-turn lanes, continuous auxiliary lanes, and service roads, will be determined by MDOT SHA on a case-by-case basis. The design shall be based on AASHTO geometric design guidelines and accepted engineering practices, addressing the anticipated traffic safety and operational conditions.
4.7.2 Center Turn Lane – MDOT SHA may require the permittee to provide a center-turn lane for handling left-turn traffic where warranted to address traffic impacts from development. Typical applications include urban highways with closely-spaced, full-movement access points for which individual left-turn bays are not feasible and for which minimal queueing of left-turning vehicles is anticipated. While center-turn lanes are sometimes established on 2-lane and multilane undivided highways, often through retrofit of new pavement markings, their use will not be considered on divided highways or highways pending construction of a raised median.
4.7.3 Service Road – Appropriately designed permanent or temporary service road segments may be required in connection with proposed access where necessary to address future highway needs.
4.8.2 Layout – On-site curb shall be constructed along parking areas, drive aisles, and other areas subject to motor vehicle traffic. It shall be located beyond the ultimate reserved or dedicated right-of-way required for future public road improvements with allowance made for local zoning or setback requirements. MDOT SHA identifies the ultimate section based on MDOT SHA planning studies, design plans, or the Highway Needs Inventory, as applicable. When back curb is required instead of on-site curb, the following guidelines apply:
Construction of new or modified highway medians may be required in order to restrict, discourage, or prevent certain turning movements in and/or out of the site. This requirement is determined by evaluating the safety and traffic operations issues presented at each point of access. Median installation and modifications most commonly include:
Requirements will be determined for the specific location on a case-by-case basis. The design of all medians shall comply with AASHTO geometric design guidelines and MDOT SHA standards. Suggested geometric layouts for the most common median openings are provided in the typical details in Standard Road Widening and Paving Details.
Sidewalk along a state highway may be required by MDOT SHA, the local government, or both in connection with a request for state highway access. In either case, the sidewalk construction and/or reconstruction along the state highway(s) will be required and included in the Access Permit. Once constructed, sidewalks are maintained and repaired by the political subdivision in which they are located, not by MDOT SHA. The design must conform to MDOT SHA's and the local government's requirements.
4.10.2 Location – The location of the sidewalk shall be determined using practices approved by the appropriate local jurisdiction and/or MDOT SHA. Typically, the sidewalk is to be constructed parallel to and behind curb-and-gutter. A 6’ grass strip between the back of curb and the sidewalk is desirable.
4.10.3 Width – Standard width for sidewalk constructed within the state right-of-way is 5' minimum.
4.10.4 Americans with Disabilities Act (ADA) Compliance – All sidewalk facilities constructed within state right-of-way, regardless of the local jurisdiction's requirements, shall comply with ADA standards and practices. Refer to 4.11 Exceptions and Special Cases for additional information and reference to guidance documents.
Exceptions to the requirements of this chapter may be considered for the following applications, upon receipt of proper supporting documentation, which may include a traffic study. Upon review of a properly-supported appeal, MDOT SHA’s decision will be final. No further appeals will be considered once this decision is rendered.
4.11.2 Previously-Improved Highway Frontage – The requirement for construction of dedicated turning lanes to exclusively serve the site access may be waived for development along previously-improved highway frontage at the sole discretion of MDOT SHA upon acceptable demonstration of at least one of the following requirements (A, B, or C):
4.11.3 Channelization Requirements Not Waived – Where the requirement for site-specific turning lanes is waived, frontage improvements may still be required. These may include replacement of existing curb-and-gutter at a new offset to establish a usable shoulder, comply with current bicycle compatibility standards, ensure proper drainage, address maintenance concerns, or accommodate a planned typical section improvement on the state route. An example of a planned typical section improvement is the conversion of a 4-lane undivided section to a 5-lane section with continuous left-turn lanes or a raised median.
4.11.4 Multi-Lane Highways – In general, widening for new acceleration and deceleration lanes for the proposed site access is not required on existing closed-section highways with 6 or more existing travel lanes (3 in each direction), unless the need is identified in an approved traffic impact study or a highway capacity improvement is identified in the Consolidated Transportation Program. This exception shall not apply where precluded by safety considerations.
4.11.5 Development in Sensitive Areas – Developments in historically, environmentally, or culturally sensitive areas, as determined by MDOT SHA, will be evaluated on a case-by-case basis. Widening may be waived or reduced in scope, subject to the same conditions as identified in Section 4.11.2 Previously-Improved Highway Frontage above. Frontage improvements may still be required.
4.11.6 Low-Volume Commercial Traffic Generators – The following guidelines may be applied to small-scale commercial development along low (2,000 ADT) to moderate (5,000 ADT) volume highways, at the discretion of SHA, unless a safety issue results:
4.11.7 Limited Use or Specific Purpose Access – Access that will have use limited to specific time periods or by specific vehicles will be evaluated on a case-by-case basis to determine the scope of site access improvements required. Examples include mining/land reclamation operations, seasonal business operations, temporary business establishments, timber harvesting operations, school bus entrances, loading dock access, telecommunications tower sites, unmanned utility facilities, etc. MDOT SHA may require the full scope of improvements normally required in any case.
4.11.8 Frontage Improvements for Site Redevelopment – The requirement for existing site frontage to be improved is determined on a case-by-case basis for redevelopment projects. To the degree to which substandard features or conditions are present, their significance to the safety and operations of the state highway and the extent to which the redevelopment may exacerbate them are prime considerations for MDOT SHA. Where no compelling safety, capacity, or operational issue exists, the overall scope of the project is the main consideration. Complete site reconstruction generally requires the same improvements as new construction would, whereas minor site renovations to support a different use may only trigger entrance improvements.
4.11.9 Special Hardship Situations – From time to time, special situations occur which warrant a restrained approach to the application of access requirements. Relief may be possible for the following situations:
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