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Access

Article

Intersection conflicts
Source: FHWA

Access refers to the demand for vehicular entry and exit to and from driveways and crossroads that intersect with an arterial. These driveways and crossroads are commonly referred to as access points. Access points present a number of planning and design challenges and potential hazards along the roadway. Each access point represents a potential conflict between turning and through-moving vehicles, pedestrians, and bicycles on the arterial, as illustrated in the diagrams at right. Greater access point density

Intersection conflicts
Source: FHWA

increases the number of potential conflicts along an arterial.

Access management refers to the regulation of access point location and spacing and is a crucial part of creating a great street that is safe for all modes. Access management is intended to balance mobility for through-traffic and access for vehicles attempting to enter or leave the roadway, while ensuring maximum safety for all users. Typically, a roadway's functional classification guides the location and spacing of access points.

Access management plans must be site-specific and place-based. The figureat rightdepicts the traditional relationship between access and functional classification.

Mobility vs Access figure
Source: FHWA

At the top of the functional class hierarchy (principal arterial freeways), mobility is provided at the expense of access; at the bottom (the local road system), extensive access is provided, which limits mobility. Planning and designing great streets requires finding the most appropriate balance between access and mobility, according to place type. While local guidelines can sometimes be useful, standard solutions based solely on functional classification rarely produce desirable outcomes.

Tradeoffs are inherent in every roadway access point decision. Balancing competing interests is critical to successful implementation, and is perhaps one of the biggest challenges in designing great streets. Allowing unlimited access points would undermine the safety and efficiency of the arterial street. Conversely, prohibiting all access would render adjacent properties essentially worthless.

Arterial vs. local vs. collector
Source: FHWA

Access must be considered on a case-by-case basis. The owning transportation agency (the state, county, or local municipality), controls access rights along roadways within a jurisdiction. Most agencies have policies in place to regulate new and existing access point development. Nonetheless, access plays such a critical role in determining the environment along a roadway that planners, designers, and stakeholders are encouraged to carefully examine projects on a case-by-case basis.

Site-specific conditions and community objectives should always be taken into account when deciding how to manage and control roadway access. Specific spacing requirements will vary based on site-specific conditions. The ITE Traffic Handbook Table 10-5 provides guidance for minimum spacing requirements.

MoDOT's Access Management Guide identifies four major goals of access management:

  • Improve roadway safety
  • Improve traffic operations
  • Protect taxpayer investment in the roadway
  • Create better conditions for non-motorized modes of travel

MoDOT emphasizes that the guidelines are intended to allow for flexibility when necessary, and their overarching goal is to provide a safe and efficient transportation system while balancing the need for access to abutting land uses. Broad standards should not be applied without careful consideration of a project's unique characteristics.

Traffic impact studies should consider the large-scale transportation network (current and planned) before access permits are granted. Developers are typically required to conduct a traffic impact study before gaining approval for new developments. Unfortunately, each individual development usually conducts its own study, failing to capture the cumulative impacts of all proposed developments in the area. In such cases, a project may be approved because its impact on the roadway seems reasonable, but the combined impact of several projects can create traffic problems along the arterial.

Access forSmall Town Downtowns:

Characteristics that influence access in small town downtowns:

  • Accentuated access-mobility conflict
  • Lower travel speeds
  • Numerous smaller parcels abutting the roadway
  • Significant pedestrian presence

Small town downtowns are unique place types.In most cases, they are located in regions that are more rural in nature. They oftenserve as central goods and service providerswithin their respective rural regions, drawing a fair amount of final destination traffic.The main streets of these small towns are often stateroute arterials that play an important role in the regional road network,usually resulting in a highvolume of traffic traveling through the small towndowntown area on the way to other destinations.As a result, therecan beconflicts between access and mobility along small towndowntown corridors.

This conflict has an immediate impact on access in small town downtowns. Lower speeds in small town downtown areas are essential for a variety of reasons such as improvinga driver’s ability to perceive and react to conflicts created by access points. See Design Speed for more information.Although specific spacing requirements will vary based on speed, local codes and conditions, Table 10-5 in the ITE Traffic Handbook is a good place to start for minimum spacing guidance.

Another residual effect of the access-mobility conflict in small town downtowns is related to vehicles desiring to turn from the street into one of the abutting parcels or crossroads. Deceleration lanes allow these vehicles to pull out of the through-travel stream before turning, resulting in safer traffic operations on the arterial. This treatment may necessitate acquiring additional right-of-way, and the potential impacts to adjacent parcels should be considered. The added width may also cause problems for pedestrian crossings.

Small town parcels
Credit: CH2M HILL

Small town downtowns are typically comprised of numerous small commercial or retail parcels, as shown in the image at right. Because providing each parcel with a separate access point is not usually practical, small town downtown commercial areas rely heavily on foot traffic.

Patrons walk to businesses from nearby neighborhoods, nearby parking lots, or on-street curb parking. Transit is typically not present. The access points of primary concern in small town downtowns are at the crossroads.

Due to the nodal nature of these place types, there are usually not very many crossroads intersecting the street. Where crossroads do intersect, they are eithersignalized or unsignalized. Many small town downtowns will have one primary intersection at the center of town. Depending on traffic demand, the intersection may be signal or stop controlled. If multiple traffic signals areneeded, they should be spaced at least one-quarter mile apart along small town downtown corridors.

Access Image
Credit: CH2M HILL

Unsignalized intersections occur more frequently in small town downtowns -at minor crossing roads, parking lot entrances, and commercial driveways.

Typically, traffic on the lower volume/minor road is controlled by a stop sign, allowing traffic on the major arterial to flow freely.

Unsignalized crossroads with more traffic and a greater number of turning movements (> 50 vehicles per hour in the peak hour) should consider adding deceleration lanes on the arterial street.

Pedestrian signage
Credit: CH2M HILL

Access points create conflicts for through-moving vehiclesand pedestrians.Drivers attempting to enter the arterial from a driveway are often fixated on traffic approaching from the left, and may edge out onto the arterial without looking back to the right to check for pedestrians.In areas with a significant pedestrian presence, the number of driveways should be minimized to the extent practicable. At higher volume access points, signage reminding drivers to watch for pedestrians can be used to minimize conflicts, as shown in the image at right.

Raised medians with accommodations for pedestrian crossings can be an effective measure to reduce the number of access-related conflicts along small town downtown arterial streets. Raised medians restrict left turn movements to only the access points across from an opening in the median. Access to driveways is confined to right-in, right-out movements, reducing the number of potential conflicts from nine (9) to three (3) at a standard 3-legged intersection (see Oregon PDF for additional detail on right-in, right-out channelization design).

Median u-turn
Credit: CH2M HILL

Raised medians also provide the opportunity for attractive landscaping that can aesthetically enhance the roadway (see the safety section of this guide for more information about issues related to trees or other fixed objects in the median). When raised medians are used, it may be appropriate to allow u-turn movements at select locations to provide sufficient access to both sides of the arterial, as in the image at right. Simple and highly visible signing can help drivers navigate these maneuvers, provided that sight distance is maintained.

Intersection diagram
Source: ITE Traffic Handbook

Many small town downtown corridors include a few businessesthat cater to traffic passing through town on a regional trip, such as gas stations and fast-food restaurants. These types of businesses should be located at intersections where access can be provided via a crossroad to minimize conflicts on the arterial resulting from direct driveway access. If a corner lot is not available and direct access is required, driveways should be spaced as far from intersections and other driveways as practicable, as shown in the diagram at right.

The need for direct driveway access points along major arterials can be minimized by providing access along lower speed crossroads or backage roads. Shared access, or the consolidation of access for multiple businesses, can improve the efficiency and safety of small town downtown corridors. Shared access drives should be monitored, though, to ensure that the access point is not being used excessively and causing congestion on the arterial.It is important toremember that the number of driveways along an arterial street is proportional to the crash rate.