Location and Geometric Design of Refuge Areas on Managed Lane Corridors
Managed lanes (e.g., high-occupancy vehicle (HOV) lanes, toll lanes, bus-only lanes) are increasing in use throughout the United States. In many cases, these lanes are implemented within the previously existing footprint of the roadway, offering little shoulder or buffer width adjacent to the lanes themselves. On corridors where, essentially, the full roadway width is used as travel lanes, disabled vehicles can effectively render one or more travel lanes unusable and thereby reduce the effectiveness of the Managed Lanes. In these situations, provision needs to be made for disabled vehicles to be removed from the travel lanes. One treatment often mentioned is to provide “pull-outs” or “refuge areas”. In some cases, where drivers suspect an
impending disability of the vehicle (e.g., imminent engine failure or
negotiable flat tire), they may be able to carefully drive the vehicle for a short
distance to reach a refuge area. In other cases, such as an empty gas tank, a sudden severe mechanical failure, or a crash, the vehicle may be completely and suddenly immobilized with no chance to exit the travel lane.
The objective of this research is to produce a set of
proposed guidelines to aid practitioners in designing managed lane corridors to
better accommodate disabled vehicles.
The guidelines would include recommendations on cross-section dimensions
as well as recommended location and spacing of refuge areas. The products developed in this project should
be in a format that can be readily integrated into future editions of existing
design manuals and guidebooks at the national and state levels.
Providing accommodation for disabled vehicles on freeway managed lanes
is a vital design element that provides both safety and operational
benefits. As more managed lane corridors
are being considered and implemented in the United States, the applicability of
such guidelines increases substantially.
While the consideration of refuge should definitely be a consideration
in managed lanes on new alignments, it is equally important (if not more so)
for retrofit alignments on existing freeways, where right-of-way is often
constrained. These provisions will fill
a current gap in design guidance provided by the AASHTO Green Book and the AASHTO HOV
Guide, as well as state-level design manuals that include consideration of
managed lanes. Members of AASHTO’s Technical
Committee on Geometric Design have expressed interest in this topic and would
likely incorporate results of this project into their consideration for future
reviews of a the AASHTO Green Book.
Guide for High-Occupancy Vehicle Facilities (2004) covers HOV planning,
implementation, operation, and design on both freeways and arterials. An
expanded number of issues were addressed that formulated wider potential application
and implementation strategies including commercial truck lanes and lane
conversions. To make the guide easier for practitioners, major types of designs
are separately presented alongside commensurate access, enforcement, signing
and pavement marking provisions.
However, the timing of this guide did not permit a detailed discussion
of a number of emerging topics. Some
topics were ahead of their time and did not represent any or few on-the-ground
examples, such as truck lanes and general purpose lane conversions to HOV. The guide was based on the best practitioner
experience at the time, and most accepted standards of practice were covered.
However, no research was conducted on design or operation issues; the majority
of the guide borrowed heavily from other relevant and recent resources
including NCHRP Report 414 (1998) and State DOT input.
Having one of the largest legacy freeway
HOV systems implemented by any State, Caltrans has authored several guidance
treatises dating from 1991. The 1991 guide was more of an orientation to HOV
lanes with guidance provided for design and operational trade-offs. More recently policy directives have been
issued as interim updated guidance affecting such topics as access options and
design treatments until such time that a new comprehensive guide is drafted and
adopted. The current (2003) Caltrans
guidance is the most extensive of any State, and the legacy of guidelines
through the decades tracks extensive operational experience and in-state
supported research into such topics as ingress/egress, enforcement best
practices, and performance. However, even with that historical basis, the
Caltrans HOV guidelines are essentially silent on the provision for
accommodating disabled vehicles and mitigating their effects on adjacent
Some of the tasks that could be completed in
this project include:
· Complete a comprehensive review of recent literature
review and existing guidelines focused on design features similar to refuge
areas on managed lanes. These design
features could include provisions for freeway “breakdown lanes” or motorist
assistance accommodation on freeway shoulders, and the review of guidelines
should include guidelines used in other countries, to consider accommodations
they may use in Active Traffic Management treatments (e.g. hard shoulder
· Review existing design criteria of travel lanes and
shoulders for managed lane corridors across the United States. This review should include a comparison of recommended
widths for lanes and shoulders for barrier- and buffer-separated facilities.
· Consult with practitioners (e.g., road agencies,
emergency service providers) to determine current practices for responding to
disabled vehicles and maintaining traffic flow in existing managed lane
corridors. Practitioners should be based
in different areas of the country to provide geographical variety.
· Consider potential effects of revised design guidelines
on implementation of new managed lane corridors.
· Propose new text based on the results of the research
project for the next editions of the AASHTO Green
Book, AASHTO HOV Guide, and/or
state design manuals.
The guidelines developed with this research could apply to a variety of state and national guidance documents on the design of managed lane facilities.
There is a need for guidelines on the design and operation of such managed lane features. The appropriate spacing, geometric design, and operational characteristics of these refuge areas should be researched to determine how those already constructed are operating and provide guidance to locate and design future pull-outs for optimal performance.
Additional considerations may include:
· A perceived increase in disabled vehicles in many urban areas, possibly due to economic conditions where people are keeping their vehicles longer, increasing the likelihood of mechanical breakdown.
· Desired spacing and optimal location for pull-outs may not be available due to the constraints that do not allow sufficient width of right-of-way, nor expansion of the right-of-way, to provide full shoulders and/or buffers in the original design of the managed lane corridor.
· Desire of police to use “pull-outs” as enforcement areas, both for checking compliance with lane use restrictions and for crash investigation, and the effect that has on the geometry of the site and on the safety of enforcement officers and their vehicles.
|Sponsoring Committee:||AKD10, Performance Effects on Geometric Design
|Research Period:||12 - 24 months|
|RNS Developer:||Marcus Brewer, Tracy Borchardt, Jim Brewer, Kay Fitzpatrick, Brooke Struve|
|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) and AHB65 (Operational Effects of Geometrics), in conjunction with the AASHTO Technical Committee on Geometric Design. Problem Statement # 2015-C-07 on the NCHRP/AASHTO SCOR list.|
|Index Terms:||Highway design, Geometric design, Managed lanes, Disabled vehicles, Refuge areas, Road shoulders, Traffic lanes, |
Operations and Traffic Management
Safety and Human Factors