Recurring Traffic Bottlenecks: A Primer
Focus on Low-Cost Operational Improvements (Fourth Edition)
Chapter 1. Introduction
When Did "Plan on Being Delayed" Become Part of Our Everyday Lexicon?
Delays due to traffic congestion seem like an unavoidable, frustrating fact of life. Or are they—unavoidable, that is? Why must we accept to allow 30 minutes for what should be a 15 minute drive? In today's world, drivers increasingly factor in time just to sit in traffic—which is caused not by us, mind you, but by "others" who, if they would only get out of our way, would free up that trip to its rightful duration.
This document focuses on traffic congestion caused by bottlenecks—which are specific locations on the highway system where the physical layout of the roadway routinely cannot process the traffic that wants to use it and results in localized, recurring congestion. While some of the nation's congestion can only be addressed through costly major construction projects, there is a significant opportunity to apply more operational and low-cost infrastructure solutions to provide relief for localized, recurring congestion at bottlenecks. This document, Recurring Traffic Bottlenecks: A Primer—Focus on Low-Cost Operational Improvements, describes such bottlenecks and explores opportunities for near-term, operational, and low-cost methods to correct them.
Purpose of the Primer
This primer's focus on alleviating localized, recurring congestion at bottlenecks distinguishes it from other resources addressing other types of congestion. In general, congestion can be either localized (occurring at distinct segments of roadway) or systemic (occurring throughout the roadway system due to widespread excess demand), and either recurring (occurring routinely at the same place and/or time) or nonrecurring (occurring non-routinely due to unplanned, unforeseen, or special events such as weather events, crashes, football games, etc.). Congestion can even occur when there is no apparent reason, witness that on a seemingly clear highway a "phantom" traffic jam may occur. (This is discussed later in the document.) Different types of congestion have different causes and, therefore, different remedies. By focusing solely on relieving localized, recurring congestion at bottlenecks, this primer can help agencies identify the right fix for a particular bottleneck. What's more, the right fix for a localized, recurring bottleneck is usually spot-specific, more effective, less expensive, and faster to implement than building a new facility.
The Localized Bottleneck Reduction Program
This document is a fourth-generation primer that is a key resource within the Federal Highway Administration's (FHWA) Localized Bottleneck Reduction (LBR) program. The LBR program provides a virtual forum for peer exchange between members of the transportation community interested in alleviating bottleneck congestion. Initiated in 2006, the program is designed to expand the portfolio of bottleneck reduction tools available to transportation agencies to encompass innovative, readily adoptable strategies for reducing congestion at bottlenecks. The first and second editions of this primer introduced, and then raised awareness about, how LBR strategies could deal with congestion, respectively. The third edition focused on providing highly specific guidance for agencies to follow in developing and advancing LBR programs. This fourth edition builds upon and updates the previous editions with recent advances in innovative research and additional case studies of implementing LBR strategies.
Why Focus on Bottlenecks?
In the past, recurring congestion was felt to be a systemic problem (either "not enough lanes" or "too many cars"). It is true that additional lanes are often needed as part of bottleneck improvements to handle the additional recurring traffic buildup, but those additional lanes are typically short subordinate segments, and not longer, uniform highway segments. Traditional capital solutions grew from a "build our way out" mindset, resulting in extensive corridor-wide "mega" improvements that could be accused of overbuilding the solution sometimes (e.g., widening a 12-mile long facility when only interchanges 3, 10 and 12 were the problem). The problem is that funding for these large scale projects is limited and they take a long time (many years) to complete, so addressing recurring congestion takes a backseat to either safety-related concerns, or out-year projects meant to enable entire regions.
However, like weather, traffic is an ever-evolving "front." And, like weather forecasting, traffic management is a dynamic moving target that makes it an ever-evolving profession. So, as with weather forecasting, we are getting better and better at it, but remain at the whim of these unrelenting fronts. Along these lines, transportation professionals have come to realize, with increasing attention, that highway bottlenecks—for example, points where traffic flow is restricted due to geometry, lane-drops, weaving, or interchange-related merging maneuvers—demand special attention.
The percentage of congestion attributable to bottlenecks varies by location and context. FHWA has estimated that 40 to 80 percent of congestion can be attributed to limited physical capacity, depending on the density of the area (i.e., urban vs. suburban vs. rural areas). In many of these situations, capacity can be greatly improved by treating localized recurring bottlenecks rather than implementing large scale corridor-wide improvements. Especially given that LBR strategies are relatively inexpensive and quick to implement, bottlenecks and LBR strategies warrant more attention than they have traditionally been given. After all, what do most Americans want, more than anything, from their government? At least according to one Northern Virginia study, the top request of residents is relief from traffic congestion by a nearly 2:1 margin over the next issue (housing affordability) and other issues like crime, education, and jobs.
Unclog That Bottleneck!
Recurring congestion accounts for an estimated 40 to 80 percent of congestion nationwide, depending on whether it is rural, suburban, or densely urban. Localized bottlenecks are often the main source of the recurring congestion problem, and they are easy and inexpensive to treat, especially compared to "megaprojects".
We need to fix the "bends, kinks, and cavitations" in the traffic "plumbing" before building more expensive and time-consuming highway expansion projects.
When agencies shift their focus from recurring congestion being primarily systemic (and thus treatable with only large projects or time-shifting strategies such as telecommuting, mode-shift to transit, etc.) to also being caused by specific chokepoints, a wider range of improvement strategies become possible, especially in the short term. While these will never entirely replace the need for corridor-wide fixes—especially at the "mega bottlenecks" such as freeway-to-freeway interchanges—localized bottleneck reduction strategies can provide a significant amount of faster and more cost effective congestion relief.
Finally, the 2008 economic downturn caused a major shortfall in revenues to transportation agencies that still persists today. In this climate, the low-cost nature, and quick turn-around timeframe, of LBR strategies has made them highly attractive alternatives to traditional large-scale capacity expansion projects for agencies seeking "to do more with less." Especially when combined with other low-cost operations and demand management strategies, LBR strategies are a major tool for addressing congestion cost effectively.