Efficient Use of Highway Capacity Summary
Report to Congress
Chapter 5: Final Remarks
This report was developed to summarize the implementation of safety
shoulders as travel lanes as a method to increase the efficient use
of highway capacity. Its purpose is to provide a succinct overview of
efforts to use left or right shoulder lanes as temporary or interim
travel lanes. As part of this summary, information related to the impact
of shoulder usage on highway safety and/or accidents during operations
was reviewed as well. The report provides critical information that
the FHWA can use to formulate guidance for agencies on providing temporary
shoulder use as a means of increasing roadway capacity. The study that
generated this product was conducted at the request of Congress through
the 2008 Technical Corrections Act.
Agencies need to consider a wide range of issues when determining whether
shoulder use is appropriate for a particular corridor or region. Experience
both overseas and domestically provides a wealth of experience from
which agencies can learn to make informed decisions. From the European
perspective, temporary shoulder use is only used during congested periods
when queues begin to build at bottlenecks in the system. Moreover, this
treatment is almost always deployed in conjunction with dynamic lane
control signing and speed harmonization. Furthermore, European agencies
have realized both safety and mobility benefits as a result of these
projects. While American deployments have been limited, experience has
been positive, though safety benefits have not been conclusive. The
issues that need to be considered include design—such as the treatment
at interchanges and auxiliary lanes, drainage, emergency refuge areas,
rumble strips, and ITS components; traffic control devices; and operational
and safety performance measures. In addition, maintenance concerns,
enforcement roles and responsibilities, incident response procedures,
personnel training, costs, liability and legal issues, and public outreach
and education are issues that should be examined. Careful consideration
of these issues can help ensure that a shoulder use deployment is effective
without having negative impacts on safety and operations.
The following results can be taken away from this summary:
- The use of buses on shoulders has generally significantly benefited
transit trip time reliability in those corridors where it has been
- There have been shoulder use projects that have shown bottleneck
relief at spot locations.
- Incident data provided from the U.S. seems to be inconclusive at
this point. There are safety benefits provided from the European applications.
However, the shoulder use is only a part of a much larger investment
in ATM technology and resources to manage them.
- There have been longer incident clearance times in areas that don't
have shoulders available to move incidents off the highway. Also,
responders don't have the benefit of traveling the shoulder to reach
the incident scene.
- European usage of hard shoulder running has always been accompanied
by additional ATM strategies such as dynamic lane control signals
and variable speed limits. These additional support strategies have
generally been lacking in U.S. applications.
As a result of the information gained from this study, consideration should be given to the following:
- FHWA should consider developing clearer agency guidance on the use
of shoulders. This would need to be a joint effort from the Offices
of Infrastructure (Design), Safety, and Operations (including how
the MUTCD relates to shoulder use lanes). The lack of existing U.S.
performance data would also point to the need for more research in
- Hard shoulder running was one of the ATM strategies recommended
for implementation in the U.S. from a recent international scan. As
FHWA and AASHTO develop guidance on ATM, they should clarify guidance
on temporary shoulder usage. This would include comparing the differences
in current U.S. usage to that of the European countries.
- Research and modeling for temporary shoulder use is lacking at this
time. This could be covered in research being developed for the ATM
- The results of the NCHRP/AASHTO/FHWA Domestic Scan on Maximizing
Flow on Existing Highway Facilities should be considered in the development
of shoulder use guidance.