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Executive Summary

The nation is entering the early stages of a freight transportation capacity crisis. The last several decades have witnessed steady growth in the demand for freight transportation in the United States, driven by economic expansion and global trade. But freight transportation capacity, especially highway capacity, is expanding too slowly to keep up with demand. The effects of growing demand and limited capacity are felt as congestion, upward pressure on freight transportation prices, and less reliable trip times as freight carriers struggle to meet delivery windows.

Freight congestion problems are most apparent at bottlenecks on highways: specific physical locations on highways that routinely experience recurring congestion and traffic backups because traffic volumes exceed highway capacity. Bottlenecks are estimated to account for about 40 percent of vehicle hours of delay. The balance—about 60 percent of delay-is estimated to be caused by nonrecurring congestion, the result of transitory events such as construction work zones, crashes, breakdowns, extreme weather conditions, and suboptimal traffic controls. This paper focuses on bottlenecks that cause recurring congestion.

Bottlenecks on highways that serve high volumes of trucks are "freight bottlenecks." They are found on highways serving major international gateways like the Ports of Los Angeles and Long Beach, at major domestic freight hubs like Chicago, and in major urban areas where transcontinental freight lanes intersect congested urban freight routes.

This white paper is an initial effort to identify and quantify, on a national basis, highway bottlenecks that delay trucks and increase costs to businesses and consumers. The paper is the first to look specifically at the impacts and costs of highway bottlenecks on truck freight shipments.

A truck bottleneck is defined by a combination of three features: the type of constraint, the type of roadway, and the type of freight route. A truck bottleneck may be caused by congestion at an interchange on a freeway serving as an intercity truck corridor, or a truck bottleneck may be caused by poorly timed traffic signals at intersections on an arterial road that serves as an urban truck corridor.

These highway truck bottlenecks can be identified and differentiated from general traffic bottlenecks. A relatively comprehensive inventory of highway truck bottlenecks can be made using available FHWA Highway Performance Monitoring System (HPMS) data and Freight Analysis Framework (FAF) data. The impact of these bottlenecks can be measured by total truck hours of delay, hours of delay to large trucks making longer-distance trips, and the tonnage and value of commodities in the trucks.

We located and estimated truck hours of delay for 14 types of highway truck bottlenecks. These bottlenecks accrue significant truck hours of delay, totaling upwards of 243 million hours annually. At a delay cost of $32.15 per hour, the conservative value used by the FHWA's Highway Economic Requirements System model for estimating national highway costs and benefits, the direct user cost of these bottlenecks is about $7.8 billion per year.

Table ES.1 lists the types of bottlenecks and the annual truck hours of delay associated with each type. The bottleneck types are sorted in descending order of truck hours of delay by constraint type (e.g., interchange, geometry, intersection, and capacity) and then within each group by the truck hours of delay for each bottleneck type.

Table ES.1 Truck Hours of Delay by Type of Highway Freight Bottleneck
Bottleneck Type National Annual Truck Hours
of Delay, 2004 (Estimated)
Constraint Roadway Freight Route
Interchange Freeway Urban Freight Corridor 123,895,000
      Subtotal 123,895,000*
Steep Grade Arterial Intercity Freight Corridor 40,647,000
Steep Grade Freeway Intercity Freight Corridor 23,260,000
Steep Grade Arterial Urban Freight Corridor 1,509,000
Steep Grade Arterial Truck Access Route 303,000
      Subtotal 65,718,000
Signalized Intersection Arterial Urban Freight Corridor 24,977,000
Signalized Intersection Arterial Intercity Freight Corridor 11,148,000
Signalized Intersection Arterial Truck Access Route 6,521,000
Signalized Intersection Arterial Intermodal Connector 468,000
      Subtotal 43,113,000
Lane Drop Freeway Intercity Freight Corridor 5,221,000
Lane Drop Arterial Intercity Freight Corridor 3,694,000
Lane Drop Arterial Urban Freight Corridor 1,665,000
Lane Drop Arterial Truck Access Route 41,000
Lane Drop Arterial Intermodal Connector 3,000
      Subtotal 10,622,000
      Total 243,032,000
* The delay estimation methodology calculated delay resulting from queuing on the critically congested roadway of the interchange (as identified by the scan) and the immediately adjacent highway sections. Estimates of truck hours of delay are based on two-way traffic volumes. However, the methodology did not calculate delay on the other roadway at the interchange. This means that truck hours of delay were calculated on only one of the two intersecting highways or two of the four legs on an interchange, probably underreporting total delay at the interchange. The bottleneck delay estimation methodology also did not account for the effects of weaving and merging at interchanges, which aggravates delay, but could not be calculated from the available HPMS data. Estimates have been rounded to the nearest thousand.
The HPMS sampling framework supports expansion of volume-based data from these sample sections to a national estimate, but does not support direct estimation of the number of bottlenecks. Estimates of truck hours of delay are based on two-way traffic volumes. Estimates have been rounded to the nearest thousand.
Source: Cambridge Systematics.

Of the four major types of bottlenecks analyzed, highway interchange bottlenecks ("interchanges on freeways serving as urban freight corridors") account for the most truck hours of delay, estimated at about 124 million hours annually in 2004. The direct user cost associated with interchange bottlenecks is about $4 billion per year.

The truck hours of delay at individual highway interchange bottlenecks are significant. The top 10 highway interchange bottlenecks cause an average of 1.5 million truck hours of delay each. Of the 227 highway interchange bottlenecks, 173 cause more than 250,000 truck hours of delay annually. By comparison only a few dozen of all the other truck bottlenecks cause more than 250,000 truck hours of delay annually (e.g., of the identified highway truck bottlenecks, only 12 steep-grade bottlenecks, one lane-drop bottleneck, and two signalized intersection bottlenecks accrue more than 250,000 truck hours of delay).

Figure ES.1 shows the location of highway interchange bottlenecks for trucks. The bottleneck locations are indicated by a solid dot. Most are located at urban Interstate interchanges. The size of the open circles accompanying each dot indicates the relative annual truck hours of delay associated with the bottleneck. These highway interchange bottlenecks delay metropolitan and local truck traffic, but they also delay national and international truck flows because they sit astride many of the key intersections of the nation's long-haul and transcontinental freight corridors.

Figure ES.1 Major Highway Interchange Bottlenecks for Trucks

Map of the continental United States showing a network of interstate highways. Highway interchange bottlenecks are indicated by a solid dot, with open circles sized to indicate the truck hours of delay on an annual basis. Population centers along the East coast, in the Midwest, and on the West coast states account for the vast majority of bottlenecks for trucks.
Source: Cambridge Systematics, Inc.

Highway freight bottlenecks, especially interchange bottlenecks, are of Federal interest because they are a significant national problem for trucking and the efficient operation of the national freight transportation system. Highway interchange bottlenecks affecting trucking are widely distributed across the United States along Interstate freight corridors. The primary truck delay on these nationally significant routes is in the major urban areas, including major international trade gateways and hubs such as Los Angeles, New York, and Chicago, and major distribution centers such as Atlanta, Dallas-Fort Worth, Denver, Columbus (Ohio), and Portland (Oregon). These urban interchange bottlenecks create sticky nodes that slow long-distance truck moves along Interstate and other National Highway System regional, transcontinental, and NAFTA freight transportation corridors.

Our findings and conclusions suggest that FHWA may wish to consider the following recommendations.

Freight bottlenecks are a problem today because they delay large numbers of truck freight shipments. They will become increasingly problematic in the future as the U.S. economy grows and generates more demand for truck freight shipments. If the U.S. economy grows at a conservative annual rate of 2.5 to 3 percent over the next 20 years, domestic freight tonnage will almost double and the volume of freight moving through the largest international gateways may triple or quadruple. Without new strategies to increase capacity, congestion at freight bottlenecks on highways may impose an unacceptably high cost on the nation's economy and productivity.

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