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 implemented.
- 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 this area.
- 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 program.
- 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.