Appendix C

Impact of Changes in Highway Capacity on Truck Travel

LANCE R. GRENZEBACK

Cambridge Systematics, Inc.

The impact of changes in highway capacity on truck travel in metropolitan areas is discussed in this appendix. At issue is whether highway capacity improvements induce truck travel and, conversely, whether restricting highway capacity dampens truck travel. The answers are needed to inform the debate about the impact of changes in highway capacity on congestion, air pollution, and energy consumption.

Changes in highway capacity include the addition of physical capacity to existing facilities (e.g., more lanes), the addition of operational capacity (e.g., better management of traffic flow through traffic engineering or road pricing), and the addition of new facilities to the highway network (e.g., construction of new highways or bridges).

For the truck driver, these improvements result in changes in travel time (i.e., faster trips), changes in travel reliability (i.e., more predictable trip times), or changes in accessibility (i.e., the ability to physically reach new areas and new markets). Where highway capacity is reduced, the changes result in slower trips, less predictable travel times, and restricted access to markets.



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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Appendix C Impact of Changes in Highway Capacity on Truck Travel LANCE R. GRENZEBACK Cambridge Systematics, Inc. The impact of changes in highway capacity on truck travel in metropolitan areas is discussed in this appendix. At issue is whether highway capacity improvements induce truck travel and, conversely, whether restricting highway capacity dampens truck travel. The answers are needed to inform the debate about the impact of changes in highway capacity on congestion, air pollution, and energy consumption. Changes in highway capacity include the addition of physical capacity to existing facilities (e.g., more lanes), the addition of operational capacity (e.g., better management of traffic flow through traffic engineering or road pricing), and the addition of new facilities to the highway network (e.g., construction of new highways or bridges). For the truck driver, these improvements result in changes in travel time (i.e., faster trips), changes in travel reliability (i.e., more predictable trip times), or changes in accessibility (i.e., the ability to physically reach new areas and new markets). Where highway capacity is reduced, the changes result in slower trips, less predictable travel times, and restricted access to markets.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Over time, the truck driver, the motor carrier firm, and eventually the shipper will react to these changes by adjusting their travel behavior and changing their use of the highway system. They may reallocate their trips—shifting the hour or day that a trip is made, changing the route, and changing the destination; or they may make new trips, take longer trips, and shift freight between truck and rail or truck and air. By altering the total truck miles of travel and its allocation between congested and uncongested roads, changes in highway capacity can increase or decrease congestion, engine emissions, and energy consumption. The general impact of changes in highway capacity on truck traffic is examined in the first section of this appendix. The author argues that, in the short term, changes in highway capacity are not likely to result in significant changes in truck travel. The three major reasons for this argument are the marginal nature of most changes in highway capacity today, the moderate exposure of trucks to severe congestion, and the overriding influence of low freight transportation costs. Reviewed in the second section is the fragmentary evidence on the specific responses of motor carriers to changes in highway capacity, the primary ones being changes in the time of travel, route, and mode. Structural changes in the economy, freight logistics, and trucking that may make truck travel more sensitive to changes in highway capacity in the future are discussed in the third section. These trends include a shift toward longer and more time-sensitive supply chains and distribution networks that leave trucks exposed to congestion and a countervailing shift toward the use of information technology to improve the productivity and flexibility of freight transportation. In the fourth section research findings are reviewed on the relationship between truck accidents and congestion, which suggest that reducing peak-period congestion may reduce the frequency of common accidents, but will have little effect on the frequency of major truck accidents, which tend to occur during uncongested off-peak periods. The state of truck travel modeling and the data available to transportation planners and engineers to analyze trucking issues are reviewed in the fifth section. In the final section the author's conclusions are summarized and the implications for highway capacity planning, air quality, and energy use are discussed.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use The conclusions rely heavily on empirical data from planning and policy studies and on anecdotal information from the freight and motor carrier industries. Although a large body of academic and applied research on many aspects of freight logistics and trucking exists, there is little on the topic of induced truck travel. Almost all of the work on travel demand forecasting and induced traffic has been focused on automobiles and transit. Finally, the information that exists on truck travel usually pertains to large trucks, typically heavy five-axle tractor-semitrailers. There are 45.5 million trucks registered in the United States; however, 39.5 million of these trucks, or about 88 percent of that fleet, are pickup trucks, panel trucks, and minivans, many of which are used for personal transportation. For traffic and congestion management purposes, these light trucks are indistinguishable from automobiles and are seldom accounted for as trucks in urban transportation studies. The balance of the trucks in the U.S. fleet, approximately six million, or about 12 percent of all trucks, are medium and heavy trucks, ranging from local delivery trucks with two axles and six tires to large over-the-road tractor-semitrailers with five axles and 18 tires (BTS 1994, 64). (The size classes used to categorize trucks are presented in Table C-1.) In the medium and heavy truck categories, the heavy and heavy-heavy trucks (Classes 7 and 8) are the focus of most truck transportation studies. These large trucks, an estimated 2.5 million trucks, or about 5 percent of the total fleet, are thought to account for more than three-fourths of all truck miles of travel and most of the ton miles and revenue miles of travel in urban areas (Blower and Campbell 1988).1 GENERAL IMPACT OF CHANGES IN HIGHWAY CAPACITY In the short term, changes in highway capacity are not likely to result in significant changes in truck travel for three major reasons. Extensiveness of Existing Highway Network The first reason is the extensiveness of the existing highway network in the United States. The aggregate contribution of the highway ca-

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use TABLE C-1 Large Trucks : 3+ Axles, Straight, or Combination (Grenzeback et al, 1988, 2). NOTE: Includes four- and five-axle trucks, weight Classes 7 and 8, greater than or equal to 26,000 lb gross vehicle weight.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use pacity improvements planned for the next two decades will be marginal, at best, to the overall capacity of the existing system. The highway system is composed of 3.9 million mi of roads and streets and supports a highly developed truck freight system. The 45,500-mi Interstate highway system and the 200,000 mi of other expressways and principal arterial highways (together about 6 percent of the total system) are the economic backbone of the highway system and carry the bulk of the truck traffic. Urban highways—composed of 12,500 mi of Interstates, 6,500 mi of freeways and expressways, and 52,200 mi of other principal arterials, for a total of 71,200 mi—account for 30 percent of the truck network and about 1.8 percent of all roads (FHWA 1993, 146). 2 The size of this urban system has been relatively static for the past two decades as highway funds have shifted from construction of new roads to the repair and replacement of existing roads. This pattern is expected to continue through the next two decades. From a historical perspective the highway capacity improvements being debated today will be occurring at the end of the truck era, not the beginning. When trucks were introduced at the beginning of this century, they freed industry and workers from the need to locate near rail lines, just as the introduction of railroads in the early 1800s freed industry and workers from the need to locate within dray horse–hauling distance of ports, rivers, and canals. In both cases the new transportation technologies led to sharp drops in the cost of moving goods and contributed to profound changes in the structure and dynamics of cities. The push to improve farm-to-market roads in the 1930s and the decision to build a full intercity-Interstate highway network in the 1950s and 1960s provided the basic highway capacity that supports the trucking industry today. None of the highway capacity improvements currently planned are comparable to these programs and none will significantly reduce the average cost of truck freight movement. They will make marginal improvements to specific corridors and relieve critical bottlenecks; however, they will not fundamentally restructure the economics of trucking. Limited Exposure of Trucks to Congestion The second reason that changes in highway capacity are not likely to result in significant changes in truck travel is the modest exposure of

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use trucks to congestion. Most truck travel is not exposed to severe congestion and therefore is not highly sensitive to marginal changes in travel time and travel reliability. Truck travel is spread more evenly across the day than commuter traffic, with relatively more truck trips than automobile trips made during uncongested off-peak hours. Changes in highway capacity designed to facilitate or restrict peak-period automobile travel will have little effect on off-peak truck travel. A 1988 study of truck traffic in Los Angeles, San Diego, and San Francisco, California, found that large trucks accounted for less than 5 percent of vehicles on the freeways during the peak periods (Grenzeback et al. 1988, 1).3 The percentage and the absolute number of large trucks on the freeways were highest during the midday off-peak period (see Table C-2 and Figure C-1). A subsequent study of large-truck traffic on city streets in Los Angeles resulted in similar findings (JHK & Associates 1989).4 A parallel analysis of California Department of Transportation annual average daily traffic data for all freeway segments in Los Angeles, San Diego, and San Francisco found that the “worst” freeway segments (i.e., those with high traffic volumes, high injury rates, TABLE C-2 Large Trucks as a Percentage of Total Vehicles (One Direction) (Grenzeback et al. 1988, 8)   LOS ANGELES SAN DIEGO SAN FRANCISCO MORNING PEAK (7:00 TO 9:00 A.M.) Weighted Averagea 3.8 1.8 4.2 Observed Range 0.5–17.2 0.7–5.7 0.8–13.2 MIDDAY OFF-PEAK (11:00 A.M. TO 1:00 P.M.) Weighted Averagea 5.5 2.5 5.4 Observed Range 0.7–16.2 0.6–4.8 0.6–12.1 EVENING PEAK (4:00 TO 6:00 P.M.) Weighted Averagea 2.6 0.8 2.4 Observed Range 0.2–13.2 0.1–1.9 0.3–6.8 a Average traffic volumes during the evening peak period were slightly higher than average traffic volumes during the morning peak period. Midday traffic volumes were 10 to 15 percent lower than the peak-period volumes.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use FIGURE C-1 Large truck and total traffic volumes on I-5 northbound at Los Feliz Boulevard, Los Angeles (Grenzeback et al. 1988, 8).

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use and severe congestion) tended to have a lower percentage of large trucks (2.86 percent on average in Los Angeles) than all other freeway segments (4.0 percent on average in Los Angeles) (Grenzeback et al. 1988, 5). A 1992 count of truck traffic on the Capital Beltway in the Washington, D.C., metropolitan region found that large trucks (three or more axles) averaged 3.0 percent of all vehicles during the morning peak period (6:00 to 9:00 a.m.) and 2.3 percent during the evening peak period (4:00 to 7:00 p.m.). The range of observed percentages was 1.5 to 4.5 percent during the morning peak and 1.25 to 4.0 percent during the evening peak (Zilliacus 1993). Two reasons account for the lower percentages and lower absolute numbers of trucks on the road during the morning and evening peak periods. The first is cost: it costs $20 to $60 per hour to operate a large truck in an urban area (Grenzeback and Warner 1994, 4–9). 5 When possible, truck drivers and motor carrier firms schedule and route trips to minimize congestion delays, which result in increased travel time and cost. The pressure to minimize costs is especially strong in the for-hire motor carrier industry, for which interstate operations were deregulated in 1980, triggering strong price and service competition. The second, and usually dominant, factor determining truck exposure is the business cycle of the clients—the shippers and receivers of goods. The business operations of many industries work to insulate trucks from the morning and evening peak traffic periods. For example, consider the operation of a downtown retail department store. The primary market for a downtown department store is mid-day walk-in shoppers. Because the peak business time is the midday, sales employees start later in the morning than office workers and therefore tend to commute later in the morning peak period. Truck deliveries are usually made during the evening and at night when parking space is available at loading docks and store staff are free to handle new merchandise. Likewise, maintenance, cleaning, restocking, and display are done late at night or early in the morning so that they do not interfere with daytime sales. Suburban department stores operate on a different cycle. Their primary market is evening drive-in traffic, usually split around the afternoon commute and dinner hours. Sales staff work overlapping

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use shifts, but tend to commute outside peak traffic hours. As with down-town stores, maintenance, cleaning, and restocking are done late at night or early in the morning, but truck deliveries are made during the midday off-peak period so that they do not interfere with the afternoon or evening sales periods. As a consequence of these business cycles, only a fraction of all truck movements serving major department stores at downtown and suburban locations is likely to be exposed to substantial congestion. Similar patterns are evident in other trucking operations, including petroleum distribution. Tank trucks delivering gasoline and home-heating fuel account for a large number of local truck movements in urban areas. Home-heating fuel trucks are loaded at tank farms during the midday or evening, and deliveries are made the next morning or afternoon to comply with local noise ordinances that restrict truck deliveries in residential areas to daylight hours. Gasoline tankers serving metropolitan areas tend to be loaded at tank farms during the afternoon, and deliveries are made in the evening or at night when business slacks off at local service stations. In both cases exposure to severe congestion is minimized, but primarily because of client needs, not travel time or cost considerations that would be affected by improvements in highway capacity. By contrast, couriers, parcel services, and less-than-truckload carriers, such as Federal Express, United Parcel Service, and Roadway, operate in a much different business environment, which leaves their pick-up and delivery operations exposed to peak-period traffic congestion. These carriers distribute inbound freight during the morning peak period as offices and retail stores open and pick up outbound freight during the afternoon peak period as their clients close out the business day. This pattern persists because few offices and retail stores ship or receive sufficient volumes of freight to justify the cost of employing a night shipping clerk, dock worker, and security officer. As a consequence, these carriers operate during the peak periods and are very sensitive to local highway capacity changes. For businesses that are open at night, some firms and their motor carriers make nighttime deliveries. Hotel and restaurant provisioners, including bakery, dairy, meat, and produce truckers, sometimes deliver at night; however, the primary incentive is often uncongested parking and open docks, not lack of traffic congestion per se. A study

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use of United Parcel Service operations found that the cost of the parking tickets that its trucks received in downtown Boston during the day was five times greater than the cost the firm incurred on those routes because of traffic congestion (Warner and Wilson 1989). In summary, the trucking industry is highly fragmented. The exposure of trucks to congestion and their response to highway capacity improvements is determined by the industries they serve, their geographic range, whether they operate fixed or variable routes, the time sensitivity of their shipments, and the size and sophistication of the fleet. This diversity has tended to spread truck travel more evenly across the day than automobile travel, making trucks generally less sensitive to changes in highway capacity. Low Freight Transportation Costs The third reason for the limited impact of highway capacity changes on truck travel is the overriding influence of low freight transportation costs. Changes in highway capacity result primarily in changes in travel time and reliability. For a motor carrier these changes are accrued directly as increased (or decreased) labor and vehicle operating costs and indirectly as changes in the level of service that can be offered to shippers and receivers. Carriers are sensitive to changes in travel time, and therefore driver time, because labor costs [payroll, benefits, and purchased transportation (i.e., leased owner-operators)] account for almost 60 percent of operating expenses. Fuel purchases account for a smaller proportion of operating expenses, about 8 percent, but both labor and fuel costs have escalated rapidly during the past decade. In the for-hire trucking industry, which accounts for a large share of truck miles of travel and for which statistics are available, labor costs rose 40 percent and fuel costs rose 50 percent between 1986 and 1991 (BTS 1994, 115). Despite these cost increases, overall freight transportation costs have dropped relative to the gross national product (GNP) and other producers' prices (BTS 1994, 58). Because transportation costs typically account for 1 to 4 percent of total production costs in the manufacturing and retail industries, low freight costs have made it more attractive for shippers and receivers to substitute transportation for

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use higher cost labor, materials, and land.6 The outsourcing of manufacturing and assembly work to Asia and Mexico and other Latin American countries depends on long, but relatively inexpensive, transportation supply lines to realize large savings on labor. Just-in-time manufacturing and distribution substitute more frequent truck deliveries to factories and retail stores to reduce the cost of carrying extra inventory. Similarly, the emergence of exurban distribution and warehousing centers reflects business decisions to increase expenditures on truck, rail, and air transportation to obtain access to low-cost and easily developed land, which is more available on the periphery of metropolitan areas. In general highway capacity improvements have played a small role in driving down transportation costs and making such substitutions possible. The dominant factors are discussed in the following paragraphs. Evolution of air freight services using all-cargo air freighters and the belly-freight capacity of commercial wide-body passenger air-liners. Air freight service has captured and expanded the market for very-high-value and time-sensitive shipments, outperforming trucking. Since the 1950s the air freight share of national freight ton miles has grown tenfold from 0.03 to 0.37 percent, for which the air freight industry now receives 4 percent of national freight revenues. By comparison, trucks account for 25 percent of the national ton miles and receive 79 percent of national freight revenues (BTS 1994, 58,59). The trucking industry percentages are expected to remain stable or decrease slightly during the next decade and the air freight share of tonnage and revenues is expected to increase. Introduction of containerization and very large container ships (i.e., post-Panamax container ships). Containerization has reduced damage and pilferage of goods in transit and reduced the cost of labor required to load and unload shipments. Automation and economies of scale in ship design have sharply reduced the cost of moving a container across the Atlantic or Pacific oceans. Development of double-stack rail service on unit trains. Double-stack service has halved the cost of long distance (i.e., greater than 1,200 mi) intermodal rail container shipments. Rail rates per ton

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use FIGURE C-5 Composite profile of reported incidents by type (Cambridge Systematics, Inc. 1990). high accident rates at low traffic volumes that are typically the result of single-vehicle, often fatal, involvements that occur at night and high accident rates at high traffic volumes that are typically the result of common accidents that occur during the day. As highways approach saturation levels with stop-and-go traffic conditions, the accident rate is thought to drop as travel speeds fall.13

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use The distribution of truck accidents and the relationship between truck accident rates and congestion levels appear to follow the general patterns just described with some significant variations: trucks are involved in more common accidents than cars because they are less maneuverable in congested conditions; they are involved in more accidents during the midday than cars because relatively more trucks operate during that time; and they are involved in more fatal accidents than cars because of their greater size and weight. [The nationwide accident rate for trucks has dropped during the past decade. The fatal accident rate for medium and heavy trucks dropped by 39 percent despite a 42 percent increase in truck miles of travel during that period, but trucks are still involved in a disproportionately high percentage of fatal accidents (21st Century Trucking: Profiles of the Future 1994; BTS 1994, 138).] An analysis of truck incidents on Los Angeles freeways found that 50 percent of all reported truck incidents were caused by breakdowns, stalls, broken fan belts, flat tires, and the like, whereas 30 percent of truck incidents were common accidents, typically involving side-swipes and rear-end collisions (Recker et al. 1988). Five to 10 percent of truck incidents were found to be major incidents, which were defined as truck-involved accidents or spills requiring the closing of two or more lanes of freeway for 2 hr or longer. The remaining 10 percent of reported incidents were attributed to debris on the roadway. Major truck accidents were most often the result of overturns, spills, and shifted loads; they were usually fatal and caused extensive property damage. They tended to occur on freeway ramps, the primary cause being excessive speed on the curve. Most major accidents occurred during off-peak periods—at dawn when traffic volumes are low and trucks travel at full speed, or at midday when trucks and other vehicles operate at full freeway speeds. By contrast, common accidents, usually involving sideswipes and rear-end collisions, tended to occur during peak periods. Overall, it was estimated that 90 to 95 percent of truck incidents occurred on weekdays, 70 to 80 percent during the daytime, and about 50 percent during the midday period when truck volumes, and therefore truck exposure on the freeways, were highest. These findings suggest that increasing highway capacity and smoothing traffic flow during congested peak periods may reduce the rate of common accidents for both cars and trucks and the substan-

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use tial delay and economic costs of these incidents; however, the findings also suggest that increased highway capacity alone may do little to reduce the frequency of major truck accidents, both because fewer trucks operate during peak periods and because most major accidents occur at night or at midday when trucks operate at full speed. MODELING TRUCK TRAVEL There are many approaches, all relatively simple, to truck trip modeling. Some regional travel demand models, particularly in smaller urban areas, do not differentiate between trucks and automobiles. The current models are descended from the urban transportation planning system suite of models developed during the 1960s and 1970s to help size new highway, and later, transit, projects. The forecast horizon for these models was typically 20 years, and a substantial margin of error was expected because of the difficulty of accurately anticipating underlying land use and socioeconomic trends. Trucks (especially large trucks) were known to account for a relatively small proportion of all traffic (e.g., 5 to 10 percent of total vehicles). Because this is well within the margin of error of the models, transportation modelers did not push to develop separate or accurate truck forecasts. Many regional model systems today estimate vehicle trips from person trips, usually based on observed behavior. After total vehicle trips are estimated and assigned to roadways on the metropolitan network, the link traffic volumes are apportioned among trucks and automobiles. The more detailed models use current traffic counts by functional class of roadway as the basis for estimating the percentage of trucks in the traffic stream; less developed models use a single estimated percentage for major roads only, largely disregarding local and small truck travel. To account for the size difference among trucks and cars, most traffic assignment programs perform calculations in passenger-car-equivalents (PCEs), then convert these units to vehicles by equating an automobile to one PCE, small or medium trucks to two PCEs, and large trucks to three PCEs. A few of the larger and more advanced metropolitan areas have refined this process by developing separate trip tables for trucks and automobiles. Chicago, for example, has developed a separate truck trip table for its regional model on the basis of extensive surveys of

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use shippers and motor carriers in the region. This permits the Chicago Area Transportation Study, the metropolitan transportation agency, to model the impact of major changes in highway capacity (e.g., new roads, major widenings, truck access restrictions) on truck miles of travel and to approximate the subsequent air quality and energy impacts. Phoenix has recently developed a similar truck modeling capability, and other metropolitan areas have developed partial truck trip tables for corridor or area analyses, but these are the exceptions rather than the rule. The overall state-of-practice with respect to truck travel modeling is very modest. The two major hurdles to development of more sophisticated truck travel models are the general lack of data on freight and truck movement and the complexity of freight demand estimation and truck trip modeling. The lack of data reflects the historic focus of metropolitan transportation agencies on automobiles and passenger transit and the difficulty of collecting the data. Local transportation agencies have had no mandate or funding to deal with trucks, except as they affect down-town parking and loading zones. For the most part, truck travel has been viewed as a private-sector responsibility that is of concern to state agencies primarily for revenue, safety, and size and weight regulation. The Intermodal Surface Transportation Efficiency Act of 1991 mandates greater attention to freight transportation and more private-sector involvement in the planning and programming of highway improvements; over time this will lead to a more sophisticated understanding of freight movement and truck travel, which will be reflected in better data collection programs and regional travel models. In the interim, however, current and reliable data on commodity movements and truck travel patterns at the metropolitan level are scarce. (At the national level there are good aggregate data on commodity and freight movement and sophisticated analytical models for economic policy issues such as size and weight regulation, but again, only limited data and modeling capability to analyze the impact of freight system capacity changes.) The second hurdle is the complexity of freight movement and truck travel modeling relative to passenger and automobile travel modeling. Freight modeling lacks a definable common unit, such as a traveler, that can be used across all freight demand analyses. Freight

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use is measured and forecast variously in tons, units, and value, forcing transportation and logistics planners to develop separate (and usually incompatible) models by commodity and carrier. Freight does not aggregate well for travel demand and behavior modeling purposes, as can be done by using households or commuters for passenger transportation modeling. Freight mode choice modeling is complex and must often be modeled at the commodity, industry, and sometimes firm level to produce acceptable results. Freight trips, especially local truck pick-up and delivery trips, are often chained trips, with trucks making dozens of stops across a metropolitan area during an 8- to 10-hr work day. Such trips can be described and modeled individually (e.g., using routing and dispatching software), but the techniques for effectively handling thousands of chained trips within a regional model are not yet available. (This problem is common to activity-based passenger modeling as well.) Freight trips typically extend beyond the geographic scope of metropolitan transportation agencies. One area may see the container as it lands at a seaport, a second as it moves through on a rail car, and a third as it moves by truck from a rail terminal to a warehouse. Few agencies have the resources to track and represent such multimodal trips into regional travel models. Overall, regional travel models are not well equipped to forecast changes in truck travel as a result of changes in highway capacity within metropolitan areas, except by treating trucks as automobiles. This is adequate to evaluate the impact of limited highway capacity changes, such as lane widenings, on general travel times, but the changes cannot be tied back to specific types of trucks, industries, or commodities. The models are not capable of anticipating the impact of economic demand management techniques, such as road pricing or emission pricing schemes, on trucks because the models do not incorporate shipper demand or motor carrier behavior models. Where the highway capacity changes studied are modest in scale and limited to a single definable corridor, the shortcomings of the models can be compensated for by direct interviews with industries and motor carriers. For larger projects in complex metropolitan areas, planners must

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use develop truck trip tables or forego detailed analysis of the impacts of highway capacity on truck travel. CONCLUSIONS AND RECOMMENDATIONS In the short term changes in highway capacity are not likely to result in significant changes in truck travel. With a well-developed highway system in place, the demand for truck travel is determined primarily by the overall level of economic activity in a metropolitan area and the area's role in the national and global economy. Deregulation of the transportation industry and technological innovations outside trucking have pushed down the cost of transportation relative to labor and materials, making shippers less sensitive to changes in highway capacity at a metropolitan scale. Moreover, the business cycles of many industries work to insulate trucks from the morning and evening peak traffic periods, resulting in truck travel that is spread more evenly across the day than is the case with automobile travel. This leaves trucks less exposed to peak-period congestion and less sensitive to changes in highway capacity designed to facilitate or restrict peak-period travel. This pattern makes it unlikely that air quality and energy conservation goals for trucks can be achieved solely by manipulating highway capacity. Internal economic pressures within the trucking industry may achieve what changes in highway capacity cannot: relative reductions in truck miles of travel, engine emissions, and energy consumption. Deregulation of the trucking industry has induced shippers to expand their use of trucking, but it has also triggered strong competitive pressures within the trucking industry to reduce costs and improve productivity. During the next decade trucking will carry more freight with fewer trucks and fewer truck miles of travel relative to the past decade and the years before deregulation. The productivity improvements will come in vehicle and engine design, vehicle and driver use, and administration. The effects of these improvements will be most pronounced in long-haul intercity truck traffic where freight can be shifted to rail and less pronounced in short-haul metropolitan distribution operations where rail is not, and will not be, a cost-effective competitor.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use The public sector should take advantage of these internal economic pressures to accelerate the trucking industry's move toward more productive operations. Effective programs might include removal of physical and regulatory barriers within metropolitan areas that result in circuitous truck routes and excessive truck miles of travel, tax incentives to retire high-emission trucks, and training programs to introduce automated routing and dispatching programs to small trucking fleets as part of urban ITS programs. The great majority of trucking firms in metropolitan areas are in small fleets of 5 to 25 trucks; like many small businesses, they have the flexibility to innovate quickly, but seldom have the sophistication or resources to explore and transfer new concepts and new technologies. For these programs to be effective, they must be targeted and designed for specific industry and motor carrier groups, and they must involve the shippers who buy trucking services as well as the motor carriers who provide them. These efforts must be coupled with aggressive enforcement programs aimed at putting unsafe truck drivers and firms out of business. Working against these programs will be long-term pressures on the trucking industry to increase truck miles of travel, absorbing much of the remaining capacity of today's highway system. The key forces will be continuing dispersion of business and housing across metropolitan areas, which will expand the service area that trucking firms must cover; changing land values, which will push warehouses and truck terminals toward the periphery of metropolitan areas; adoption of just-in-time manufacturing and retailing practices, which will generate more truck trips; and globalization of trade, which will produce growing demand for long, time-sensitive supply chains and distribution networks. To address these forces, metropolitan areas must develop a more integrated approach to freight transportation planning. Basic research is needed to describe and forecast the following: Freight generation rates by industry and commodity that can be tied to specific land uses and industrial facilities. Which industries generate freight and how much? Trip patterns by industry and commodity across carriers. Where does the freight come from and where is it going? Who carries it and where is it transferred from one mode to another?

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Economic behavior of trucking firms. How do motor carriers make truck routing and dispatching decisions and terminal location decisions? Engine emissions and energy consumption by engine, body type, and duty cycle. Many more combinations of engines, body types, and duty cycles exist within the truck fleet than the passenger car and light truck fleets. What are the most prevalent combinations in urban areas and what are their emission patterns? This basic research will not immediately produce models that forecast the impact of changes in highway capacity on truck travel, but it will provide planners and policy makers with a better understanding of the interrelationship of economic development, land use, freight transportation, and environmental quality. This understanding is necessary for informed decisions about the appropriateness and effectiveness of land use, tax, and regulatory policies. Concurrent research is needed to develop more sophisticated regional travel models, particularly corridor-scale models, that can accommodate multiple truck trip tables and truck networks. However, focused models with the potential for practical application should be encouraged over comprehensive models because of the complexity of freight transportation. NOTES 1. Using data from the National Truck Trip Information Survey (Blower and Pettis 1988), this study estimates that large trucks account for 79 percent of all truck travel (excluding travel by light trucks, such as pickups and panel trucks) within the 15 large urban areas that were surveyed. 2. Under the provisions of the Intermodal Surface Transportation Efficiency Act of 1991, about 155,000 mi of Interstate and other economically critical arterials will be designated as the National Highway System. 3. For the purposes of the study, a large truck was defined as having three or more axles and a gross vehicle weight rating of 26,000 lb or more. Truck counts and classifications were made from video tapes of traffic flows at 78 urban freeway sites across the three cities. Counts were made of two-axle, six-tire trucks, but not reported because the California legislature had specified a study of large, three-or-more-axle trucks. The distribution of two-axle, six-tire trucks was similar to the distribution of the large trucks.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use 4. This follow-on study used the same sampling, video-taping, and classification methodology as the Urban Freeway Gridlock Study (Grenzeback et al. 1988). 5. The average value of time for truck drivers is estimated to be approximately $20.00 per hour ($15.65 per hour for four-tire trucks, $21.54 per hour for six-tire trucks, $16.99 per hour for three- to four-axle trucks, and $19.63 per hour for combination trucks). The cost estimates, in 1990 dollars, include hourly wage rates, fringe benefits, an allowance for overtime, and adjustments for vehicle occupancy. American Trucking Associations officials have suggested that the cost of operating a truck may be as high as $60 per hour when union wages and depreciation of the tractor and trailer are taken into account. None of these estimates include the opportunity cost of time lost to receivers because of congestion delays. 6. Cambridge Systematics, Inc., estimates based on national and state input-output tables. See also 21st Century Trucking: Profiles of the Future 1994, VI-3 and Figure VI-2. In this report, Mercer Management, a contributing author, estimates that transportation accounts for 6.4 percent of the 1992 U.S. gross domestic product (GDP). Total logistics costs, including warehousing, administration, and other inventory carrying costs are estimated to be 10.9 percent of GDP. 7. Data are available for eastbound truck crossings only; the Port Authority does not charge drivers traveling westbound across the Hudson River. 8. The federal Surface Transportation Assistance Act of 1982 (STAA) established a de facto interstate-standard truck by declaring that trucks meeting specified size and weight standards could operate without restriction on the national system of designated truck routes (i.e., Interstate highways, specified arterials, and access roads). The STAA effectively preempted the states' rights to regulate the size and weight of trucks in interstate commerce as long as those trucks operated on the Interstate and designated access routes. The net effect of the STAA and the economic pressures felt by motor carriers to improve the productivity of their drivers and tractors has been to push carriers toward larger capacity five-axle trucks or smaller, more maneuverable three-axle trucks, reducing the demand for midsize four-axle trucks. States still regulate the size and weight of trucks operating in intrastate commerce and may authorize the use of heavier or larger trucks within a state under special permit arrangements. 9. Cambridge Systematics, Inc., field interviews conducted for the Port Authority of New York and New Jersey and the California Department of Transportation under various projects, 1987 through 1990. 10. Estimates prepared by Dr. Paul O. Roberts of Transmode Consultants, Inc., for Cambridge Systematics, Inc., and reported in work by Cambridge Systematics, Inc. (1994, 3–7). 11. The intelligent transportation systems (ITS) commercial vehicle operations (CNO) programs involve automated clearance and verification of

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use truck credentials (e.g., registration, operating authority, fuel tax permits, oversize-overweight permits), automated weighing (weigh-in-motion), and may eventually incorporate automated roadside safety inspection technology and on-board vehicle diagnostics and driver-fatigue monitoring systems. Most size, weight, and safety inspections are done on rural Interstates and state highways. ITS CVO systems will improve state productivity and minimize delays and congestion for motor carriers at weigh stations and ports-of-entry, but will have little impact on urban congestion and urban truck movements. 12. These estimates are drawn from Incident Management, a study of metropolitan traffic and highway incident management programs prepared for the Trucking Research Institute of the American Trucking Associations by Cambridge Systematics, Inc. (1990). The estimates are based on interviews with police and highway officials; case studies of traffic and incident management programs in Chicago, Fort Worth, Los Angeles, Minneapolis, and New York; incident management program records; and available studies, including Incident Characteristics, Frequency, and Duration on a High Volume Urban Freeway (I-10, Los Angeles) (Giuliano 1988). 13. For a summary of the literature, see work by Campbell et al. (1994) and Hall and Pendleton (1989). Hall and Pendleton discuss urban freeway accident rates and congestion in Appendix C (pp. 22, 23) of their study. REFERENCES ABBREVIATIONS BTS Bureau of Transportation Statistics FHWA Federal Highway Administration Blower, D.F., and K.L. Campbell. 1988. Analysis of Heavy-Duty Truck Use in Urban Areas. UMTRI-88-31. Transportation Research Institute, The University of Michigan, Ann Arbor, June 30, 76 pp. Blower. D., and L.C. Pettis. 1988. National Truck Trip Information Survey. UMTRI-88-11. Transportation Research Institute, The University of Michigan, Ann Arbor, March, 88 pp. BTS. 1994. Transportation Statistics Annual Report. U.S. Department of Transportation, Jan. Cambridge Systematics, Inc. 1990. Incident Management. Prepared for Trucking Research Institute, American Trucking Associations . Cambridge, Mass., Oct. Cambridge Systematics, Inc. 1992. Interstate Goods Movement—Trends and Issues. Prepared for Interstate Transportation Division, Port Authority of New York and New Jersey. Cambridge, Mass., May.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Cambridge Systematics, Inc. 1994. Transportation Infrastructure Improvement Study for the Greater Columbus Inland Port Program. Prepared for Mid-Ohio Regional Planning Commission. Cambridge, Mass. Campbell, B.J., R.G. Hughes, and C. Zegeer. 1994. A Discussion of Some Aspects of the Potential Impact of IVHS on Traffic Safety. Draft. April. FHWA. 1993. Highway Statistics 1992. FHWA-PL-93-023. U.S. Department of Transportation, Oct. Giuliano, G. 1988. Incident Characteristics, Frequency, and Duration on a High Volume Urban Freeway (I-10, Los Angeles). Institute of Transportation Studies, University of California at Irvine, June (reprinted May 1989). Grenzeback, L.R., W.R. Reilly, P.O. Roberts, and J.R. Stowers. 1988. Urban Freeway Gridlock Study. Prepared for California Department of Transportation. Cambridge Systematics, Inc., Cambridge, Mass. Grenzeback, L.R., and M.G. Warner. 1994. Impact of Urban Congestion on Business. NCHRP Project 2-17(5). Final Report. Cambridge Systematics, Cambridge, Mass., June. Hall, J.W., and O.J. Pendleton. 1989. Relationship Between Volume/Capacity Ratios and Accident Rates. FHWA-HPR-NM-88-02. Prepared for New Mexico State Highway and Transportation Department, Department of Civil Engineering, The University of New Mexico, Albuquerque, June. JHK & Associates. 1989. Los Angeles: Large Truck Study. Prepared for the South Coast Air Quality Management District, Calif., May. Recker, W., T. Golob, C. Hsueh, and P. Nohalty. 1988. An Analysis of the Characteristics and Congestion Impacts of Truck-Involved Freeway Accidents. FHWA/CA/UCI-ITS-RR-88-2. Institute of Transportation Studies, University of California at Irvine, Dec. Reilly, J.P., and J.J. Hochmuth. 1990. Effects of Truck Restrictions on Regional Transportation Demand Estimates . In Transportation Research Record 1256, TRB, National Research Council, Washington, D.C., pp. 38–48. Strauss-Wieder, A., G. Pfeffer, K. Kang, M.H. Yokel, R. Codd, and J.C. Nelson. undated. Warehousing in the NY/NJ Region. Business Analysis Division, Office of Business Development, The Port Authority of New York and New Jersey, New York, N.Y. 21st Century Trucking: Profiles of the Future. 1994. American Trucking Associations Foundations, Alexandria, Va. Warner, M, and N. Wilson. 1989. The Potential for Traffic Restraint Techniques in Major U.S. Cities . Progress Report Number 2. Center for Transportation Studies, Massachusetts Institute of Technology , Cambridge, Nov. Zilliacus, C.P. 1993. 1992 Count of Heavy Truck Traffic on the Capital Beltway and Other Major Highways in the Washington Region: Final Draft. Prepared for the Metropolitan Washington Council of Governments, National Capital Region Transportation Planning Board, Washington, D.C. Jan.