Developing Crash Modification Factors for Corridor Access Management
“Part D – Introduction and Applications Guidance” of the Highway Safety Manual (HSM) presents information regarding the effects of various safety treatments (i.e., countermeasures) on the roadway network. The information presented in Part D is used
to estimate the effect of a specific countermeasure on safety. These effects are then used to develop a crash modification factor (CMF) for the specific countermeasure. In addition to the CMFs developed and recorded in the HSM, the U.S. Department of Transportation Federal Highway Administration (FHWA) has also funded the CMF Clearinghouse (www.cmfclearinghouse.org) to provide a venue for transportation professionals to identify the most appropriate countermeasures for their safety needs. The CMF Clearinghouse is updated regularly with new CMFs added on a continual basis. The HSM notes that corridor
access management is one of the most critical elements in roadway planning and design and that access management is effective in helping to manage roadway access, while simultaneously preserving the safety, capacity, and speed on the surrounding roadway network. This helps to address the problems associated with congestion, capacity loss, and safety on the nation’s roadways. Corridor access management is also identified as one of nine general proven safety countermeasures as part of the FHWA’s proven safety countermeasures initiative (http://safety.fhwa.dot.gov/provencountermeasures/pc_memo.htm). Even though corridor access management is considered to be effective in helping to manage the roadways across the nation and to preserve safety, Part D of the HSM only includes three CMFs associated with corridor access management, specifically potential crash effects of reducing access
point density. The CMF Clearinghouse helps add to the number of CMFs related to corridor access management where as of January 2014 there were more than 250 CMFs related in some way to corridor access management. These CMFs cover a wide range of topics related to corridor access management and the associated benefits related to corridor access management. Although the CMF Clearinghouse provides a large number of CMFs related to corridor access management, this large number in many ways complicates the benefit to the practitioner in trying to determine how best to apply CMFs to specific situations. There is a need to better understand the existing CMFs related to corridor access management by identifying ways to group and organize the CMFs with respect to various aspects of roadway type, geography, and other identifying conditions or features. In addition, corridor access management improvements generally include a combination of factors, which necessitates the documentation and determination of the cumulative/interactive effects of corridor access management features and the tradeoffs associated with various corridor access management features. The National
Cooperative Highway Research Program (NCHRP) Project 17-63, “Guidance for the Development and Application of Crash Modification Factors” is setting the foundation for this process in a general sense, but this needs to be built upon for corridor access management specific CMFs. The available CMFs are also concentrated on corridor improvements that may be made during design for reconstruction. Frequently, however, practitioners are confronted with questions about how adding or removing a particular access point will impact roadway safety. Providing micro-level CMFs would greatly aid highway operations and permitting personnel with making and documenting access decisions. Finally, there is also a need to develop corridor access management related CMFs for all modes (e.g., bicycle, freight, pedestrians) and for specific conflict types and severity. This would benefit all agencies who regularly assess corridor access management and would ultimately improve the application of corridor access management across the nation.
The primary objectives of this research are to:
ways to group and organize corridor access management related CMFs with respect
to various aspects of roadway geometry, geography, and other identifying
conditions or features.
cumulative/interactive effects of corridor access management features and the
tradeoffs associated with various corridor access management features (building
up on the research to be completed as part of NCHRP 17-63).
· Provide micro-level CMFs tied to corridor improvements
that may be made during design for reconstruction to aid highway operations and
permitting personnel with making and documenting access decisions.
corridor access management related CMFs for all modes (e.g., bicycle, freight,
pedestrian) and for specific conflict types and severity.
safety performance of AM features both in terms of predictive methods (Safety Performance
Functions) and CMFs.
noted, corridor access management has been identified as one of the proven countermeasures
for corridor management outlined by the FHWA.
The research outlined in this statement will provide practitioners and decision-makers with tools to evaluate impacts
of corridor access management alternatives to help them select the best
alternatives. Additionally, the research
will aid practitioners and decision-makers with ways to better document safety
benefits of corridor access management in order to help them justify access
management decisions to stakeholders.
Currently, highway access design and operation decisions
are made every day, using guidance from the HSM and the available CMFs. When these decisions involve multiple corridor
access management techniques or individual driveways, practitioners and decision-makers
are faced with uncertainty about how to apply current CMFs. This research will provide guidance in
applying CMFs for multiple related corridor access management techniques and
applying CMFs to decision about individual access points. The research results will increase the
accuracy and efficiency of design and operations decisions affecting millions
of access points each year. While this
research will help to improve best practices related to the use of CMFs, the ultimate
payoff from the research will be to improve roadway safety.
Products of this research should include
application guidance for the use of corridor access management related CMFs
from the HSM and the CMF Clearinghouse in an NCHRP study document and
additional CMFs for inclusion in the CMF Clearinghouse.
As noted, the CMF Clearinghouse includes more
than 250 CMFs related to corridor access management. These studies have included topics related to
median width, driveway density changes, reduction in access points, changes in
signal spacing, creation of directional median openings, installation of raised
medians, modification of access point densities, land use changes, and so
forth. The research on the benefits of corridor
access management is readily available, what is missing from the literature is
a concise methodology to utilize the research and subsequent CMFs most
|Sponsoring Committee:||AKD10, Performance Effects on Geometric Design
|Research Period:||24 - 36 months|
|RNS Developer:||Grant G. Schultz, Rick Laughlin, Henry Brown, Christina Hopes|
|Source Info:||Problem statement developed as a result of the Safety Effects of Geometric Design Decisions Workshop at the 2013 mid-year meeting of TRB Committees AFB10 (Geometric Design), AHB65 (Operational Effects of Geometrics), and AHB70 (Access Management).|
|Index Terms:||Access control (Transportation), Crash modification factors, Highway Safety Manual, Countermeasures, Highway safety, Transportation corridors, Highway design, |
|Cosponsoring Committees:||ACP60, Access Management|
Operations and Traffic Management
Safety and Human Factors