AM13-05(B): Approach Spacing Near a Public Appraoch on Region and District Highways with Posted Speed > 50 MPH

Type: Bulletin

Topic or Program: Access Management

Final Number: AM13-05(B)

Effective Date: 05/01/2013

Updated Date: 01/03/2022

Signature on File: Angela Kargel, Access Manangement Program Manager

This Technical Services Bulletin provides guidance for understanding and applying OAR 734-051-4020(3)(e) to existing connections and applications for new highway approaches. This guidance will help achieve greater statewide consistency in evaluating connections and approach applications for "safety and operations concerns" by increasing the understanding of the factors that are considered in applying OAR 734-051-4020(3)(e).

Connection 

An existing approach as defined in OAR 734-051-1070 (9) or an unpermitted way of vehicular access to or from a state highway and an abutting private property, city street or county road. OAR 734-051-1070(14)

Driving task

A number of discrete and interrelated activities that fall into three levels: control, guidance and navigation as defined by AASHTO "A Policy on Geometric Design of Highways and Streets.

OAR

An Oregon Administrative Rule.

Stopping sight distance (SSD) 

A standard defined in the 2011 AASHTO Policy on Geometric Design of Highways and Streets. For the purposes of this bulletin, SSD calculates a value that is the desirable spacing between a connection or proposed approach and an intersection with a public approach. In the context of OAR 734-051-4020(3)(e), the SSD value does not involve measuring sight distance triangles but is simply used as the desirable spacing.

In earlier versions of OAR 734-051, safety factors for highway approaches were generally described as:

• Roadway character
• Traffic character
• Geometric character
• Environmental character
  
• Operational character

These earlier rules did not quantify or set standards for when safety factors are met. Senate Bill (SB) 264 amended ORS 374 and established specific safety and operations concerns codified in OAR 734-051-4020(3). This bulletin addresses 4020-051-4020(3)(e) of the rule:

OAR 734-051-4020(3)(e) addresses the complexity of the driving task when a driver, traveling at a high speed, approaches an intersection and is confronted with multiple connections and potential conflicts at the same time. The intent of this rule is to avoid overburdening the driver, and thereby reduce safety risks. Simplifying the driving task is especially of concern at higher speeds. Maintaining sufficient spacing between a connection or proposed approach and an intersection with a public approach gives driver time to recognize and respond appropriately to multiple conflicts that are often present at intersections with public approaches.

This safety and operational concern arises when vehicles are travelling in a highway thru lane with a downward slope of -3% or greater, and comes into conflict with vehicles using the roadway from a connection or a proposed approach. At lesser grades, the access management spacing standards of OAR 734-051-4020(8) provide sufficient spacing between a connection or proposed approach and an intersection to meet SSD standards.

SSD is the desirable spacing along the highway between a connection or proposed approach and a public approach. SSD refers to a distance that allows a driver to perceive an obstacle on the highway, react, and stop the vehicle prior to striking the obstacle. In this case the obstacle is another vehicle using a connection or proposed approach moving into conflict with thru traffic on the highway.

It is desirable to reduce a driver's workload in the critical area around intersections where there are typically more conflicts and higher potential for collisions. The SSD, calculated using the 2011 edition the AASHTO Policy on Geometric Design of Highways and Streets, is based upon a comfortable deceleration rate, highway design speed equal to posted speed, and wet surface. The spacing calculated provides a margin of safety for a variety of driving conditions. Therefore, the minimum desirable spacing between a connection or proposed approach and an intersection with a public approach should be no less than the SSD calculated in accordance with the 2004 AASHTO methodology.

The spacing concern determined by this Bulletin only applies to a connection or proposed approach that meets all four of the following criteria. If it does not meet these criteria, then OAR 734-051-4020(3)(e) cannot be used as the basis for a safety and operations concern. The approach or proposed connection must:

• Connect to a regional or district highway.
  
• Be on a highway with a posted speed of 50 mph or greater.
  
• The section of highway dividing the connection or proposed approach and the public approach has a downward slope of 3% or steeper.
  
• The spacing from the center of the access to the center of the intersection with the public street is less than the SSD.

With the posted speed and roadway slope determined, select the SSD spacing from Table 1.

Table 1 does not contain any values for highway slopes flatter than -3% because the standard spacing requirements of OAR 734-051-4020(8) are adequate to address the stopping sight distance concerns with relatively flat or positive roadway slopes.

If all four criteria apply, the Region Access Management Engineer or other qualified staff will need to determine whether mitigation is appropriate or other factors exist that would make a lower spacing acceptable. In addition the reviewer should be aware that this safety and operations concern could be overlapped by another review standard. Thus an approach being denied or mitigated may be addressing multiple issues. In some cases, a connection may need to be closed or an application denied if the concerns with inadequate spacing cannot be sufficiently mitigated.

The department's staff working within Access Management is responsible for carrying out the guidance in this Bulletin. This includes:

• Region Managers.
  
• District Managers.
• Region Access Management Engineer.
• Development Review Coordinators.
• Access Management Coordinators.
• Permit Specialists.

Implement this Bulletin upon the effective date.

If problems or concerns develop in implementing this Bulletin, or if further clarification is needed, see attachment A or contact the Access Management Program Manager.