Access Management in the Vicinity of Interchanges, Volume 1: Practitioner’s Guide (2022)

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1   Careful management of access points along crossroads in the vicinity of interchanges can help enhance operational and safety performance at these complex transportation facility locations. As the transportation infrastructure ages and access demands increase, there is a need to optimize access. This Guide provides an overview of common interchange configura- tions and the known impacts of access management on crossroads at these locations. For a facility to have safe and efficient operations, the agency that owns the crossroad should take care to maintain the functional integrity of the roadway in the vicinity of an interchange. Closely spaced access connections result in overlapping functional areas with a complex pattern of conflict points. In many cases, low to moderate traffic volumes can produce frequent vehicular conflicts resulting in crashes, congestion, and excessive delay. This associated congestion also negatively impacts businesses near the interchange and crossroad. Methods to mitigate undesirable consequences of poor access management at these inter- change locations include: • Limiting access to the crossroad and providing direct access to individual parcels via a supporting circulation system consisting of local service roads and inter-parcel connections. • Installing a non-traversable median or median barrier to limit direct access to right-in, right-out maneuvers. • Limiting the type(s) of vehicles (passenger cars, single-unit trucks, heavy vehicles, etc.) and the volume of driveway traffic (vehicles in a 60-minute interval and within 24 hours) as a condition of the access connection permit. • Ensuring the design of the access and on-site circulation will not result in “spillback” onto the crossroad or adjacent highways. 1.1 Importance of Maintaining Interchange and Critical Road Network Junctions Efficient transportation is a critical component of economic development. The performance of an effective highway network requires the smooth functioning of all major junctions. The quality of transportation systems affects development patterns, and when efficient, they provide economic and social benefits that result in better accessibility to markets, employment, and community facilities. Within any given region, freeways are restricted to a limited number of interchanges, and each of these interchanges is important to the local network. Because an interchange functions as a junction for two significant roadways, the region around the interchange represents an opportunity for community development and economic vitality. This area often serves as a first impression of the community for visitors and the traveling public. Interchanges also provide access to jobs, connect emergency responders, and support C H A P T E R   1 The Importance of Access Management in the Vicinity of Interchanges

2 Access Management in the Vicinity of Interchanges the movement of goods and services, thereby enhancing economic development. These facilities provide critical access between communities and regions. Land use in the vicinity of interchanges often includes services that attract motorists, such as motels, service stations, and restaurants. Other commercial uses also benefit from their proximity to interchanges. In urban or urbanized areas, an interchange enhances access to businesses, such as regional shopping malls and large business parks that serve a broad customer base. Ultimately, the highway and the crossroad collectively must function seamlessly. Unfortu- nately, in many cases, the presence of numerous driveways and intersections often compromises the operational and safety performance. As the interchange area performance declines due to congestion and crashes, the value of locating near the interchange diminishes. 1.2 Importance of Access Management near Interchange Locations The primary purpose of the interchange is to move traffic efficiently to and from the highway. While the intensity of traffic can present an economic opportunity, care should be taken so that the business activity often created in the area does not cause problems and diminish the performance of the crossroad. When the surface street becomes congested, it cannot optimally deliver or absorb the traffic volumes from the highway. This inefficiency results in a diminished capacity of the interchange. An interchange and its associated crossroad corridor usually serve the following purposes: • Functions as an intersection with a major highway. • Provides a link to long-distance regional travel for both people and goods. • Maintains a connection between both sides of the highway at intervals of 1 to 2 miles. • Serves as a traveler destination area for restaurants, retail goods, hotels, and vehicle services. • Serves as a destination for the local community. • Enhances regional or global mobility. • Serves as an employment center. • Generates revenue for local government based on property and retail taxes. • Provides mobility access to and through the corridor for non-motorized users including pedestrians, bicycles, and mobility-impaired users. • Provides access and connectivity for transit users. Stakeholders, in an effort to achieve safe and efficient operation, must find ways to maintain the functional integrity of the crossroad in the vicinity of an interchange. Careful management of access on the crossroad in these interchange regions will help mitigate congestion and enhance corridor safety. 1.3 Principles of Access Management Simply stated, the primary strategy of access management is the control of the location and the design of all connection points to a roadway. The purpose is to limit conflicts between through vehicles and vehicles executing access maneuvers while also considering safe passage for other users (i.e., pedestrians, bicycles, buses). Access management may also include the management of traffic control devices, such as traffic signals, that influence the flow, capacity, and safety of the interchange crossroad. Strategies for access management include: • Reduce speed differential at access connections. • Separate turning movements from main travel lanes.

The Importance of Access Management in the Vicinity of Interchanges 3   • Provide a limited number of access connections (fewer access points translates into fewer conflict points). • Optimize spacing between driveways, resulting in fewer conflicts per mile. • Provide longer and more uniform spacing between full movement intersections. • Reduce conflict points by limiting turning movements or restricting access. Research has clearly shown that as the frequency of access maneuvers per mile increases, the number and severity level of crashes increase, and the smooth flow of traffic is disrupted. These changes reduce available traffic capacity resulting in increased travel times. Access maneuvers are a factor in over 55% of all crashes. In denser traffic areas with frequent access connections, such as near interchanges, access-related crashes can reach 70% to 75% of all crashes. When traffic signal spacing is irregular, the progression of motor vehicles becomes difficult to maintain. The intensity of land use around most urban interchanges tends to demand more traffic signals, often closely spaced and near the ramps. Accommodation of these demands along a crossroad in close proximity to an interchange results in adverse operational and safety performance. AASHTO’s A Policy on Geometric Design of Highways and Streets (referred to as AASHTO’s Green Book) is the foremost national authority on highway design (1). The 2018 Green Book recommends the use of both eminent domain and regulations to control access at locations where reasonable access cannot otherwise be achieved. In response to these adverse impacts caused by access connections, the following techniques may be applied to arterial crossroads near interchanges: • Limit the locations of left turns and have fewer left-turn locations per mile. A typical design technique is to install a non-traversable raised median where there are frequent existing access points (driveways) spaced in a less-than-optimal way. • Design each left-turn location carefully to minimize speed differential impacts between the turning and the following vehicles. This usually involves a full design-length deceleration lane for both left and right turns in addition to storage lengths. • Limit the frequency and related maneuvers for access points located in close proximity to other access points. • Plan the location of public intersections carefully to achieve uniform and longer spacing and consider the use of a variety of intersection configurations including roundabouts or restricted left-turn configurations. • Improve the accessibility of the secondary street system to provide good property access and convenient circulation of traffic to the arterial intersections. This becomes necessary, as access is limited on the crossroad. The current FHWA policy of access control is published in the Federal Register (2). It states in part: It is in the national interest to preserve and enhance the Interstate System to meet the needs of the 21st Century by assuring that it provides the highest level of service in terms of safety and mobility. Full control of access along the Interstate mainline and ramps, along with control of access on the crossroad at interchanges, is critical to providing such service. It is clear that this national policy promotes effective access management strategies; however, this does not address the recommended longitudinal distance along a crossroad that may need the critical control of access. In 2010, the FHWA distributed a document titled Interstate System Access Informational Guide (3). While it points to AASHTO’s A Policy on Design Standards—Interstate System (4), it also provides additional guidance on the application of access control to improve crossroad

4 Access Management in the Vicinity of Interchanges efficiency. The FHWA guidance document also recommends the use of the TRB Access Manage- ment Manual (AMM) from 2003. The 2014 Access Management Manual, 2nd Edition, is now available, and this updated document should be used instead of the earlier version (5). 1.4 Management of Vehicle Conflicts—Access Management as a Performance Measure Conflicts in traffic are most often those caused by access maneuvers—motorists turning left or right or crossing the highway. The location and frequency of access connections are strong influences on crossroad performance in the vicinity of an interchange. As the number of access maneuvers increases, driving on the crossroad becomes more complex, and the frequency of driver errors increases. Conflict points occur where the travel paths of road users may have a conflict with another road user. As the frequency of conflict points increases, the likelihood of crashes can also be expected to increase. As shown in Figure 1-1, a conflict point may be a location where vehicle travel paths merge, diverge, or cross. In addition, severity can be predicted using the assumption that crossing conflicts are the most likely to result in severe injuries. A method to judge or estimate the performance of alternative access plans is to quantify the conflict points created by each alter- native. This includes crossing over the street and turning left to and from the street. Merging- and diverging-related crashes are less likely to be severe. To reduce the number and severity of crashes, the number of access-related conflicts should be reduced with a focused effort to further reduce severe conflict types. 1.5 Defining “Vicinity” The vicinity for an interchange is the area for which any activity, including land use, roadway design, or traffic engineering elements, will influence the safety or operation of the interchange. Overall, the vicinity of an interchange is that area where development has occurred in response to the presence of the interchange. This means owners and developers see the value of the inter- change in terms of mobility, customer ease of use, or minimum time and distance to the freeway. In the past, the focus was mostly on the area immediately adjacent to the ramp termini, in much the same manner that the immediate area around any intersection was a consideration for impacts. Experience has shown that the typical traffic intensity of the interchange area requires much greater distances to be considered. The most critical area is the upstream and downstream functional area of the interchange ramp terminals. This is the distance from the ramp terminal in which drivers are maneuvering to (1) enter an on-ramp or (2) leave an off-ramp and enter the crossroad. It includes turn lanes Source: Williams et al. (5) (Exhibit 1-8, p. 15) Figure 1-1. Common conflict points.

The Importance of Access Management in the Vicinity of Interchanges 5   for arriving as well as departing movements. The upstream functional distance is composed of the following: 1. The distance traveled during the perception and reaction time, 2. The distance traveled to maneuver into the proper lane for turning to the ramp, and 3. Queue storage for any of the turn lanes, including entering the turn lane, decelerating, and storage. The perception-reaction time needed by unfamiliar drivers is considerably longer than that for familiar drivers. Decision sight distances in combination with geometric elements may be a potential design consideration at these critical crossroad locations. Distance recommenda- tions for decision sight distance, generally between 600 and 800 ft, can be found in AASHTO’s Green Book (1). The upstream and downstream distances are also important; this is where access activity— such as turn lanes, open medians, driveways, full movement intersections, and traffic signals— will have an effect on the crossroad. These influences can be expected to impact traffic operations in the ramp functional area. This might be where the deceleration and queuing activities of a downstream traffic signal overlap with the acceleration activity departing the ramps. Due to localized access, some crossroads have lower capacity than the interchange. This causes the crossroad to be the capacity bottleneck rather than the actual interchange. These crossroad operational challenges are usually due to traffic signals with a poor level of service. This observa- tion highlights a need to make sure the operational and safety performance of the crossroad can be maintained at the level needed to support a high-capacity interchange design that resulted from a significant investment of funds. This influence area along the crossroad demonstrates how the access management plan should consider a region that is much further than the immediate area of the interchange and associated terminal intersections. Many agencies use a ½- to 1-mile radius for both traffic and land-use planning purposes. These dimensions are largely based on the adjacent land use and require engineering judgment to establish acceptable thresholds. Often a change in the character of the road and surrounding land use dictates a change in this influence area. 1.6 Organization of the Guide The focus of this Guide is the safe and efficient design of crossroads in the vicinity of inter- changes. Chapter 1 reviews the importance of managing access at these critical locations. Chapter 2 reviews key factors associated with the various interchange configurations and terminal intersections. Individual corridor characteristics are the focus of Chapter 3. Next, Chapter 4 addresses ways to assess the access-management-related crossroad operational and safety performance. Finally, Chapter 5 presents five case studies. The appendix includes additional content that addresses methods that are policy-oriented as well as infrastructure- based techniques to consider for managing access. 1.7 References 1. A Policy on Geometric Design of Highways and Streets (Green Book), 7th ed. AASHTO, Washington, D.C., 2018, p. 1047. 2. Access to the Interstate System. Federal Register, Volume 74, Number 165, Thurs., Aug. 27, 2009, pp. 43743–43746. 3. Interstate System Access Informational Guide. FHWA, U.S. Department of Transportation (2010). Available at http://www.fhwa.dot.gov/design/interstate/pubs/access/access.pdf 4. A Policy on Design Standards—Interstate System. AASHTO, Washington, D.C., 2016. 5. Williams, K.M., V.G. Stover, K.K. Dixon, and P. Demosthenes. Access Management Manual, 2nd ed. Transportation Research Board, Washington, D.C., 2014.