Alternate Route Handbook

1. Introduction

Freeway backup. The picture shows traffic being diverted into one lane on a major freeway in an urban area.

Figure 1-1. Example of traffic diversion. (Source: Washington State DOT)

Alternate Routes

An alternate route provides additional capacity to service primary route traffic. Alternate routes begin from one point on the primary route and terminate at another point on the primary route. The terminal point of an alternate route must be downstream of the congested area. The congestion may result from some event that causes either a significant or total roadway capacity reduction or excessive, sustained traffic demand. These events may include a traffic incident, natural disaster, or emergency. These events may render a roadway facility impassable. Diverting traffic to a parallel roadway specified in a carefully planned alternate route plan provides an effective, temporary response to facilitating increased mobility and improved travel time reliability in the corridor.

Alternate routes may accommodate local and/or regional traffic. A local alternate route involves diverting primary route traffic a short distance, typically from one point (e.g., interchange or major intersection) to the next downstream point using a roadway located adjacent to the primary route. A regional alternate route typically represents a high-speed, high-capacity facility that services a primary route through traffic, destined for some location (e.g., city) far downstream of the bottleneck location, over an extended distance. The purpose of a regional alternate route is to minimize travel time and delay anticipated on the primary route or local alternate route.

The function and operation of alternate routes differ considerably from that of evacuation routes. When implemented, alternate routes must accommodate both the traffic diverted from another facility and day-to-day background traffic on the alternate route. However, evacuation routes are typically required to move large numbers of people away from a particular location. Therefore, traffic flow on evacuation routes is typically unidirectional; often, officials use uncommon traffic management strategies, such as contraflow lanes, to maximize traffic flow in one mandated travel direction. During an evacuation, officials may find it necessary to utilize parallel alternate routes to accommodate as much traffic as possible away from a particular location.

Problem Statement

The public has become increasingly sensitive to the impact congestion has on quality of life, citing delays caused by traffic congestion as its top community transportation concern in a recent national survey.¹ The 2005 Urban Mobility Report reported road users in 85 U.S. urban areas incurred $63 billion in congestion costs in 2003, resulting in 2.3 billion gallons of wasted fuel and 3.7 billion hours of lost productivity.² Congestion equates to decreased performance and, in turn, economic loss for businesses and trucking companies. Congestion either causes late deliveries or forces truckers to include additional travel time into their itineraries, particularly when making just-in-time deliveries. According to a recent Federal Highway Administration (FHWA) report, approximately 55 percent of all delays are caused by non-recurring congestion (e.g., traffic incidents, work zones, bad weather, and special events).³ The report attributes the remaining 45 percent of all delays to recurring congestion, caused by physical capacity constraints (e.g., bottlenecks) and poor signal timing. Mitigating traffic congestion involves stakeholders applying a toolbox of operations strategies and resources for managing day-to-day and event-specific (planned or unplanned) transportation operations. However, few tools represent a proactive response to mitigating nearly all sources of congestion affecting a particular roadway facility segment, without requiring significant modification between applications, than alternate route plans. Use of these plans support an underlying goal of highway system operators, to maintain travel time reliability for all system users—commuters, truckers, and bus transit.

The implementation of an alternate route plan marks a key traffic management strategy for minimizing the effect of a non-recurring congestion-causing event on traffic flow. It serves to reduce demand upstream of an event site or bottleneck through the diversion of traffic from the mainline. The location and time of such events may be known in advance, or the event may happen at random with very little or no warning. These events are commonly termed planned and unplanned events, respectively. Congestion-causing events, whether planned or unplanned, result in a reduction in roadway capacity and/or an increase in traffic demand. Table 1-1 shows the effects that both planned and unplanned events have on capacity.

Table 1-1. Congestion impacts of planned and unplanned events

EVENT TYPE		EFFECT ON ROAD CAPACITY
Planned Event	Major roadway construction and maintenance	Closes travel lane(s) or road segments. Creates side friction, reducing traffic speed and capacity.
Planned Event	Planned special event	Closes travel lane(s) or road segments to stage event (typically street use events).
Unplanned Event	Traffic incident (e.g., crash, disablement, spilled load, debris)	Blocks travel lane(s) or road segments.
	Emergency road work	Blocks travel lane(s) or road segments.
	Adverse weather (e.g., snow, ice, fog, heavy rain, sun glare)	Reduces vehicle operating speeds and increases headways, thus reducing capacity.
	Emergency (e.g., severe weather, natural disaster, human-caused incident)	Renders road segments impassable (potentially).

The following major cases of planned or unplanned event occurrences may necessitate the use of an alternate route plan:

Traffic incidents, such as serious crashes or cargo spills that possibly include a hazardous material release, causing multi-lane or total road closure.
Non-traffic incidents, such as major fires, industrial accidents, and bridge collapses, rendering sections of a roadway impassable.
Emergencies, such as a severe weather event, acts of violence, or other major catastrophe, causing road closure and/or inducing a surge of traffic demand on evacuation routes that creates bottlenecks at capacity-restrained locations.
Planned special events, such as a sporting/concert event or parade/festival, which creates an increase in travel demand and may require road closures to stage the event.
Major roadway construction and maintenance, which may close or restrict a section of roadway.

The common result of each of these events is the reduction in capacity of a roadway(s), and possibly an increase in demand, thus necessitating the consideration of alternate route implementation. Both planned and unplanned events require the same planning process to develop viable alternate route plans. A few specific examples where alternate routes proved valuable include:

After the 1994 Northridge earthquake in California, a portion of the Santa Monica Freeway (I-10), one of the world's busiest freeways, was closed. Alternate routes handled traffic that normally traversed the closed section for a 3-month period. The majority of the alternate routes represented streets located adjacent and parallel to the freeway.⁴
On Memorial Day weekend in 2002, an Interstate 40 (I-40) bridge spanning the Arkansas River in Oklahoma was hit by a barge and collapsed, which closed the State's major east-west freeway on one of the busiest travel weekends of the year. When traffic was backed up for miles on both sides of the river, officials used geographic information systems (GIS) to identify alternate routes that provided suitable access to I-40 downstream of the closed bridge.⁵
During a major reconstruction of Interstate 95 (I-95) in southeast Florida, capacity was significantly reduced. Even with six lanes open, side friction caused by construction activities significantly reduced traffic speed and capacity. In order to maintain traffic flow in the construction zone, alternate routes were used during peak traffic hours to divert traffic volume from/to I-95 and around the bottleneck location.⁶
Alternate route plans are also useful in the case of a planned special event, where traffic not destined for the event can avoid it, while traffic destined to the event can utilize the least congested route to the venue. In Atlanta, GA, an alternate route, known as the "Blue Loop," is used to divert non-attendee, background traffic away from Peachtree Street in downtown Atlanta when it is restricted due to a special event.⁷
A Chemical Stockpile Emergency Preparedness Program was developed for the Umatilla Chemical Depot in Oregon to provide alternate routes in a case where the highway is closed due to an accident involving hazardous chemicals, thus requiring traffic to be diverted around the incident site.⁸
A Hazardous Materials Response Plan was developed for the Myrtle Creek area of Oregon to prevent hazardous materials from entering the South Umpqua River due to an incident at a particular location on Interstate 5 (I-5). This plan includes alternate routes that may be implemented when certain sections of Interstate 5 are closed.⁹
In April 2004, a man abandoned his car on the San Francisco/Oakland Bay Bridge and threatened to jump. Police activity resulted in the bridge being closed for several hours, necessitating the need for alternate routes to service bridge traffic.¹⁰

Purpose

The occurrence of a traffic incident or other emergency that disrupts the normal flow of traffic places a premium on the optimal use of existing facilities. Advance planning and preparation of alternate route plans enhances the on-scene traffic management capability of interagency incident responders. Alternate route implementation affects improved safety and efficiency of highway operations under prolonged capacity restrictions and without undue impact on the surrounding community.

The development of alternate route plans has become an increasingly important component of traffic incident and emergency management programs nationwide. Agencies acknowledge a need to develop alternate route plans for the following reasons: (1) as a result of the high occurrence of serious traffic incidents such as crashes and cargo spills, (2) as a result of a major catastrophe that closed a roadway section, and (3) to be prepared for any future event. Alternate route plans represent an all-over-ops initiative applicable to multiple highway system management program areas. The same framework for selecting alternate routes and developing alternate route plans apply regardless of the motivation or anticipated application (e.g., accommodate increased travel demand, respond to sudden loss of capacity, or mitigate effects of a recurring bottleneck) of the alternate route plans for target facility segments. Alternate route plan development typically involves a transportation agency assuming a lead role with support and/or plan review solicited from affected stakeholders, such as public safety agencies, and area residents. Specifications contained in the end product must meet Federal and State standards, as applicable, for the maintenance and protection of traffic. It must also provide guidance to response personnel on when and how to deploy an alternate route and notify affected motorists.

In light of the negative effects that non-recurring congestion has on traffic operations and the need for alternate route plans, a comprehensive information source is needed by transportation engineers, law enforcement personnel, emergency management personnel, and other stakeholders charged with identifying alternate routes and preparing alternate route plans.

These alternate route plans can address the following issues:

Contingency planning for future traffic incidents at locations with a high occurrence of crashes.
Major catastrophes closing a key component of a region's highway infrastructure (e.g., high-capacity bridge, freeway-to-freeway ramp, etc.). Major catastrophes include a flood, snowstorm, earthquake, bridge collapse, act of violence, or other non-traffic incident.
Planned construction and maintenance activities.
Future planned special events.

Benefits of alternate route plan implementation include decreases in:

Secondary incidents
Vehicle fuel consumption
Vehicle emissions
Response time to traffic incidents
and other emergencies
Motorist stress levels
Aggressive driving behavior
Impact on the movement of freight
in the region
Impact on the regional economy

Approach

Various agencies utilize different criteria and guidelines in selecting alternate routes and include different information on associated alternate route plans. Often, these differences are due to different route types and the area that these routes traverse. Despite these differences, alternate routes and associated alternate route plans can be divided into four general categories:

Metropolitan—Freeway: An alternate route consisting of a freeway facility and traversing a metropolitan area. A metropolitan area is defined as an urban area with a population exceeding one million.
Metropolitan—Street: An alternate route consisting of a street facility (e.g., arterial or collector roadway) and traversing a metropolitan area.
Urban/Rural—Freeway: An alternate route consisting of a freeway facility and traversing an urban or rural area. These areas are either sparsely populated rural areas, or urban areas with a population of less than 1 million.
Urban/Rural—Street: An alternate route consisting of a street facility (e.g., arterial or collector roadway) and traversing an urban or rural area.

The alternate route planning process involves the following three phases:

Alternate Route Selection: Choosing candidate alternate routes and evaluating each route to determine the optimal alternate route choice.
Alternate Route Plan Development: Developing information to include in the alternate route plan, including information on alternate route implementation.
Traffic Management Planning: Planning for information to be disseminated to motorists during implementation and for traffic control, including capacity enhancements needed to accommodate traffic to/from and on the alternate route.

This handbook will identify minimum and ideal criteria for each phase in the alternate route planning process. Agencies that have limited resources, or that are located in urban/rural areas (characteristic of lower congestion levels and limited alternate route alternatives), may choose to follow the minimum actions. If additional resources are available, agencies, particularly in metropolitan areas with higher congestion levels and numerous candidate alternate routes, may follow the ideal actions presented in this handbook.

The literature indicates that the vast majority of alternate route plans involve diverting traffic from a freeway to a street. For this reason, the main focus of this handbook is on street alternate route plans. However, most actions that apply to the development of street alternate route plans also apply to freeway alternate route plans. In addition, actions key to developing freeway alternate route plans are also included.

Organization

This handbook is organized into seven chapters. The following denotes a brief description of each chapter:

Chapter 1: Introduction: Introduction to the concept of alternate routes and why they are needed.
Chapter 2: Background: Literature review and specific alternate route applications, including homeland security. Also includes information about and the results of the state-of-the-practice survey.
Chapter 3: Overview of Alternate Route Planning Process: A description of each of the three phases of the alternate route planning process.
Chapter 4: Alternate Route Selection: A detailed description of phase one of the alternate route planning process: Alternate Route Selection. Each step in the process includes a table describing the role of stakeholders involved and a detailed description of minimum and ideal actions.
Chapter 5: Alternate Route Plan Development: A detailed description of phase two of the alternate route planning process: Alternate Route Plan Development. Each step in the process includes a table describing the role of stakeholders involved and a detailed description of minimum and ideal actions.
Chapter 6: Traffic Management Planning: A detailed description of phase three of the alternate route planning process: Traffic Management Planning. Each step in the process includes a table describing the role of stakeholders involved and a detailed description of minimum and ideal actions.
Chapter 7: Implementation: A detailed description of decision criteria and responder activities that take place when an alternate route plan must be implemented. This chapter includes information on how to evaluate the performance of an alternate route during its operation.

Intended Audience

The successful implementation of an alternate route plan requires the coordination of a diverse group of stakeholders, each with their own knowledge and authority. This handbook is intended to familiarize the reader with the processes, barriers, and technologies associated with alternate route plan development and implementation. It is anticipated that the findings of this handbook will provide guidance for each of the stakeholders that may be involved in one or multiple phases of the alternate route planning process. In chapters four through seven, each section begins with a table detailing the roles and responsibilities of each stakeholder. Potential stakeholders include:

Transportation/public works agency
Law enforcement
Fire department
Emergency medical service
Emergency management agency
Homeland security agency
Transit agency
Turnpike/toll authority
Private towing companies
Elected officials
Planning organizations
Individuals and community groups
Major incident response team
Freeway service patrol
Media

References

Managing Our Congested Streets and Highways, Report No. FHWA-OP-01-018, Federal Highway Administration, Washington, DC, 2001, 18 pp.
2005 Urban Mobility Study, Texas Transportation Institute, College Station, Texas, 2005 [Online]. [June 20, 2005].
Traffic Congestion and Reliability: Linking Solutions to Problems, Federal Highway Administration, July 2004.
Deakin, A.K., "Potential of Procedural Knowledge to Enhance Advanced Traveler Information Systems." Transportation Research Record 1573, Transportation Research Board, Washington, DC, 1997, pp. 35-43.
Adams, J., "ODOT Gets a GRIP on Transportation," Geospatial Solutions [Online]. [September 26, 2003].
Edelstein, R., and J.A. Wolfe, "I-95 Reconstruction: A System Maintenance of Traffic Approach," ITE Journal, Vol. 59, No. 6, June 1989, pp. 39-43.
Suggs, E., "Festival to Test New Traffic Plan," Atlanta Journal-Constitution, April 8, 2003.
Emergency Operations Plan: Annex N: Chemical Stockpile Emergency Preparedness Program, Oregon Department of Transportation, May 2002.
Hazardous Response Plan, Myrtle Creek Curves, Exit 108, M.P. 108.47, Oregon Department of Transportation, District 6, Region 3.
"Unusual Incident After Action Report: Suicidal Subject on San Francisco/Oakland Bay Bridge," Memorandum, Department of California Highway Patrol, Golden Gate Division, April 5, 2004.

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