State Highway Access Manual - MANAGING HIGHWAY ACCESS


This Chapter discusses the purpose and benefits of controlling highway access and introduces access management principles that help to preserve the safety, capacity, and function of our highway system. These principles are reflected in SHA's guidelines that identify the appropriate extent of access to various types of highway facilities.

2.1 Maintaining Highway Safety

Highway safety is affected by the location and design of access points. Each access point on a highway introduces turning movements and speed changes that may be in conflict with other vehicles in the normal traffic stream of the highway. When multiple access points are located within close proximity to each other, their overlapping traffic patterns substantially increase the range and complexity of potential conflicts. Crash data consistently shows that crash rates increase in relation to the number of entrances on the highway, the intensity of roadside development, and the range of movements permitted at the access points. It is thus in the State's interest to limit access points and the range of movements available at each to those that are safe and absolutely necessary for property access. The access that can be permitted for a specific type and size of development varies with the functional and operational requirements of the highway and site-specific safety and traffic conditions.

The State requires all access points to meet certain standards in order to guard against adverse effects on highway safety. Entrances and exits that are properly located and designed allow and encourage the safe movement of vehicles in patterns which minimize interference with other traffic. With well-defined and properly engineered points of access, drivers have minimal difficulty in determining where they should enter developed properties and land uses adjoining the highway. The requirement for adequate sight distance is often a critical factor in the location of acceptable access points for sites and subdivisions undergoing development. Standard entrance designs, coupled with curb and gutter along the road frontage, help to preserve safety by promoting predictable traffic patterns and controlling unauthorized or unsafe movements. Speed transition lanes (deceleration/acceleration lanes) are typically required to separate turning vehicles from through-moving vehicles, thereby reducing the potential for rear-end collisions and improving safety.

2.2 Maintaining Highway Capacity

A highway's ability to carry traffic is influenced by the number, location, and design of access points. Turning movements and speed changes associated with access points disrupt the normal traffic flow on the highway and require speed adjustments and lane changes by other drivers. This reduces highway operating speeds and deteriorates service conditions in the normal travel lanes. As the number of access points increases, these effects become more pronounced. Closely spaced entrances, median crossovers, and traffic signals can substantially degrade the operation of highway corridors and reduce their ability to handle future increases in traffic that may be expected with regional growth.

The adverse effects that access points have on highway capacity and traffic operations can be reduced or mitigated with proper access design and the use of dedicated auxiliary lanes to serve inbound and outbound turning movements. Proper access design allows vehicles to easily move into and out of local streets and entrances along the highway, without encroaching on the through travel lanes and interfering with the regular highway traffic flow. Entrances should be designed to accommodate the full range of vehicles anticipated to use the access. Providing separate speed change lanes for slower-moving and turning vehicles reduces the speed adjustment and lane changes in the normal travel lanes and provides space for anticipated vehicle queues.

2.3 Maintaining Highway Function

A properly implemented and maintained highway system is comprised of different types of highways with varied functional requirements and desirable operating characteristics. To support these functional characteristics, each type of highway requires a different level of access control. The number of access points and range of movements that can be permitted for a given development is determined, to a large extent, by the functional requirements of the highway. For example, access may be denied or highly restricted along the State’s main highways, whereas multiple access points may be appropriate on highways that serve primarily local traffic.

Maryland's State Highway System consists of primary and secondary routes with rural and urban designations. The Primary Highway System provides the principal routes of interstate and interregional highway travel, whereas the Secondary Highway System supports both regional and local-level travel. State highways are also described by their functional classification, in accordance with U.S. Department of Transportation – Federal Highway Administration guidelines. The functional classification is indicative of the service characteristics a highway is intended to provide, based on its role in the overall highway transportation system and the regional land use context. Under this classification system, highways are classified as Freeways, Principal Arterial, Minor Arterial, Major Collector, Minor Collector, and Local. Their general functional requirements are as follows:

2.3.1 Freeways

Freeways provide the key means of interstate, intrastate, and interregional travel. On these highways, the mobility of through traffic is of paramount importance. As such, they must be able to support high volumes of traffic at high speeds over long distances. Maximum control of access is necessary to implement and preserve this function. Direct access is not allowed on freeways. Instead, traffic may enter or exit the highway only at grade-separated interchanges. There are no driveways or traffic signals, parking is prohibited, and a wide median or physical barrier separates the opposing travel lanes to maximize safety and operational efficiency.

2.3.2 Arterials

Arterial routes are designed to provide highway service through and between metropolitan areas and regions and may function as either primary or secondary routes. Connecting to freeways at strategic locations, these routes are vital to the efficient and economical movement of commuter traffic, goods, and services each day at all levels of the highway network. Their design reflects a wide range of functional requirements, including the ability to support relatively high operating speeds and traffic volumes. Arterial routes have varying degrees of access control, depending on their specific functional requirements. Access to adjacent properties is subordinate to the need to ensure mobility for through traffic on arterial routes.

2.3.3 Collectors

Collector routes provide links between local streets, land uses, and regional transportation facilities. These routes comprise the most frequent patterns of "day to day" travel within and between communities in a region and provide connection to major highways. Operating speeds are usually moderate, varied with the extent of development and direct access. These roadways often carry a moderate amount of traffic during the day, with increased traffic during the morning and evening commute periods. Access to adjacent properties and mobility of through traffic are equally important considerations on collector routes. As such, the highway characteristics vary according to the zoned land uses and development context.

2.3.4 Local Roads and Streets

Local roads and streets serve mainly to provide direct access to individual properties, for a diverse group of users. They are designed for local traffic, slow operating speeds, and numerous intersection approaches and driveways. The design of local roads and streets often emphasizes pedestrian mobility and access to businesses, community, and residential areas. Parking is often permitted on the street and refuse collection and emergency response are important design considerations.

2.4 Access Management

Transportation officials are showing more interest in access management as a means of addressing the problems presented by traffic congestion, safety issues, and the rising cost and complexity of road improvements. The U.S. Department of Transportation's Federal Highway Administration (FHWA) defines access management as, "the process that provides access to land development while simultaneously preserving the flow of traffic on the surrounding road system in terms of safety, capacity, and speed.” Access management should be thought of as an attempt to balance the need to provide good mobility for through traffic with the requirement for reasonable access to adjacent land uses.

The use of access management techniques results in safer, more efficient travel along our State highways and preserves the benefits of investment, both public and private, in the transportation infrastructure. By reducing traffic congestion in urbanized areas, safety is improved, travel times are reduced, and site accessibility is enhanced. This protects the value of private investment in development and supports the long-term appeal and vitality of business and residential land uses in already-developed areas.

2.4.1 Access Management Techniques

The following access management techniques, endorsed by FHWA, help to maintain highway safety, capacity, and function:

  • Limit the Number of Conflict Points at Driveway Locations. Points of potential conflict between different vehicular movements are good indicators of the potential for accidents at an intersection. The potential for vehicular crashes increases as the number of conflict points increases. Therefore, limiting the number of conflict points, most often accomplished by restricting certain turning movements at an access point, can be an effective safety measure. When left turns and cross movements are restricted at an intersection, the number of conflict points is significantly reduced. For example, a driveway that permits full movement access across the median of a divided highway has six points of potential conflict, whereas a driveway that permits only right turns in and out of the site out has just two points of potential conflict.
  • Separate Conflict Points. Intersections created by public streets and driveways represent basic conflict areas. Adequate spacing between these conflict areas is promoted through entrance and street spacing standards. Separating conflict areas reduces the complexity of interactions between vehicles and allows more room for drivers to negotiate speed changes and turning movements.
  • Reduce the Interference of Through Traffic. Safety is compromised when through traffic has to slow down for vehicles exiting, entering, or turning across the roadway. Turning lanes provide a dedicated area on which speed changes and turning maneuvers can occur, reducing the disruption of normal highway traffic flow. Similarly, designing driveways with large turning radii and restricting turning movements in and out of driveways reduce interference with through traffic.
  • Providing Sufficient Spacing for At-Grade, Signalized Intersections. Good spacing of signalized intersections reduces conflict areas and increases the potential for smooth traffic progression.
  • Provide Adequate On - Site Circulation and Storage. The design of good internal vehicle circulation in parking areas and proper consideration of stacking for drive-through lanes reduces the number of driveways that businesses need for access to the major roadway. Increasing the separation between the highway access point and on-site traffic conflict points reduces the possibility of traffic queuing back to the highway.

2.4.2 SHA Implementation of Access Management

Access management techniques are used to preserve and enhance many uncontrolled corridors on Maryland's Primary Highway System. Protecting these corridors is a high priority of the Maryland Department of Transportation and the SHA. SHA's Access Management Program evaluates opportunities for improving access along selected uncontrolled corridors of key primary highways. Recommended access improvements are implemented in a variety of ways:

  • Acquisition of property or access controls from willing sellers, using limited funding allocated to some corridors in the Consolidated Transportation Program
  • Development of access control concept plans with local governments to guide future access decisions in a consistent manner
  • Working cooperatively with local governments to manage access through the local land planning process.
  • Identification of access improvements that can be implemented as subdivision and development takes place and recommending these to the local approving authorities. These improvements are recommended to local government during their land use and development review process.

Access management techniques are applied routinely in the review of proposed access on all State highways, in the interest of improved safety and traffic operations. The standards discussed throughout this manual, as well as the underlying State regulations, reflect their use.