Appendix B

Review of Empirical Studies of Induced Traffic

HARRY S. COHEN

Cambridge Systematics, Inc.

The results of empirical studies of the effects of expanding highway capacity on highway system use are reported in this appendix according to the following categories:

  • Studies of specific facilities

  • Studies of areawide measures of highway supply, and

  • Studies of the travel behavior of individuals or households that can be used to estimate changes in highway system use.

FACILITY-SPECIFIC STUDIES

The travel forecasting literature includes a number of facility-specific studies of the traffic-generating effects of highway improvements. Jorgensen (1947) studied the effects of the construction of the Merritt and Wilbur Cross parkways on traffic in the corridor between New York City and New Haven, Connecticut. To estimate normal traffic



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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Appendix B Review of Empirical Studies of Induced Traffic HARRY S. COHEN Cambridge Systematics, Inc. The results of empirical studies of the effects of expanding highway capacity on highway system use are reported in this appendix according to the following categories: Studies of specific facilities Studies of areawide measures of highway supply, and Studies of the travel behavior of individuals or households that can be used to estimate changes in highway system use. FACILITY-SPECIFIC STUDIES The travel forecasting literature includes a number of facility-specific studies of the traffic-generating effects of highway improvements. Jorgensen (1947) studied the effects of the construction of the Merritt and Wilbur Cross parkways on traffic in the corridor between New York City and New Haven, Connecticut. To estimate normal traffic

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use growth in the corridor, Jorgenson examined traffic counts in the corridor for several years before the opening of the new facilities and found that they were closely correlated with gasoline sales in Connecticut. Consequently, he used information on the growth in gasoline sales after the opening of the parkways to estimate the normal growth in traffic. Using this approach, Jorgenson concluded that the parkways generated 20 to 25 percent more traffic in the corridor than would have been expected from the normal rate of growth. Lynch (1955) analyzed traffic in the Maine Turnpike/U.S. Route 1 corridor to estimate the traffic effects of opening the turnpike. He used information on the growth of traffic on major roads in Maine outside the corridor to estimate normal growth in the corridor. He concluded that 5 years after the opening of the turnpike, traffic in the corridor was 30 percent greater than would have been expected as a result of normal growth. Both the Connecticut parkways and the Maine Turnpike serve high volumes of intercity trips, and both provided significant reductions in both peak and off-peak travel times. Frye (1964a, 1964b) examined the traffic effects of the construction of the Dan Ryan and Eisenhower expressways in Chicago on the basis of a review of traffic counts and origin-destination survey data collected before and after the opening of the expressways. He found that traffic through a 5-mi screenline centered on the Dan Ryan Expressway increased by 11 percent after the expressway opened, but concluded that almost all of the increase was a result of route diversion. He found a 21 percent increase in traffic for the Eisenhower Expressway, versus a 14 percent increase in three control areas. Frye identified four factors contributing to the exceptional growth rate in the Eisenhower Expressway corridor: Natural growth: the increase in traffic in the study area that would have occurred regardless of whether the new expressways were constructed. Adverse traffic: an increase in vehicle miles of travel (VMT) on local and arterial streets that is necessary to get to or from expressway on- or off-ramps. Diverted traffic: traffic diverted from routes outside the study area to the new expressway or to local streets and arterials for which travel conditions have improved.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Induced traffic: additional trips in the study area made because of the improved level of service on both the new facility and old competing facilities. Noting the difficulty in separating the four factors, Frye expressed the opinion that little of the observed increase was due to induced traffic. Holder and Stover (1972) studied the traffic generation impacts of eight urban highway projects in Texas. They identified six components of traffic on new highways: Diverted traffic from other roads, Converted traffic from other modes, Growth traffic from increases in population, Developed traffic from changes in land use, Cultural traffic from changes in the propensity to travel resulting from socioeconomic changes, and Induced traffic from new trips made because of added convenience. For each of the eight projects, the authors compared corridor traffic growth before project opening with either regional trends or corridor growth before project completion, referring to the difference as “apparent induced traffic.” For six of the projects, estimates of apparent induced traffic ranged from 5 to 21 percent. For the other two, no evidence of apparent induced traffic was found, a finding the authors attributed to the availability of other routes offering comparable travel times in the project corridors. On the basis of their analysis, Holder and Stover made the following general conclusions: Apparent induced traffic can represent a significant portion of the traffic on a new facility; Most induced traffic occurs during off-peak hours; and If a substantial amount of induced traffic is to occur on a new facility, then the off-peak travel time must be reduced significantly or the existing facilities must be congested. Pells (1989) examined user responses to new highways in the greater London area. The methodology included measurement of traffic in the corridors in which the new highways were built before and after construction and comparison of the percentage growth in traffic

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use with the percentage growth in control corridors. Three facilities examined by Pells are discussed in the following paragraphs. A40 Westway, a 2.5-mi elevated highway in West London, was opened in July 1970 and has undergone several improvements since then. A before-and-after study conducted in May, September, and October 1970 to test the initial effects of the road revealed a 14 percent increase in traffic in the Westway corridor, versus a 2 percent increase in a control corridor during the same period. Over the long term, the differences between Westway and the control corridor were much greater. From 1970 (before the opening of Westway) to 1984, traffic in the Westway corridor grew by 87 percent, versus 10 percent for the control corridor. Pells did not discuss reasons for the low traffic growth rate in the control corridor traffic, nor did he provide any justification for why such a low growth rate should have been expected in the Westway orridor if the new highway had not been opened. A316, a major radial route in southwest London, was widened from four to six lanes in 1976. From 1974 to 1980, 24-hr two-way flows in the A316 corridor increased by 57 percent, versus 30 percent for the control corridor. From 1980 to 1983, flows in the A316 corridor increased by 3 percent, versus a decline of 2 percent in the control corridor. No reason was given for the decrease in control corridor traffic. Land use effects in West London and Heathrow Airport were noted as contributors to the high levels of growth in the A316 corridor. The two Blackwell tunnels are located in east London. One tunnel was built at the end of the last century and the second was built in 1969. From 1962 to 1982, traffic in the Blackwell corridor increased by 153 percent, versus 64 percent for the control corridor. According to Pells, the differences measured represent the combined effects of the following factors: Wide area reassignment, involving rerouting of trips from corridors external to the study area; Redistribution of trips to different destinations;

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Attraction of trips from other modes; Retiming of trips; and Generation of trips (trips that are entirely new or are made more frequently). Pells also reported on a survey of motorists using the Rochester Way Relief Road, a major new radial route in southeast London. A total of 770 questionnaires was distributed, of which 184 (24 percent) were returned. The questionnaire asked about the trip that drivers were in the course of making and how the introduction of the new route affected their behavior. Most respondents indicated that they were just changing their route. However, 3.3 percent reported a change in destination, 2.7 percent reported a change in mode, and 9.8 percent reported that they made the trip more frequently. In September 1990, the final part of M10 Amsterdam Beltway, the Zeeburger Tunnel, was opened. The Rijkswaterstaat Transportation and Traffic Research Division conducted an extensive before-and-after study (Bovy et al. 1992) of the consequences of this project for travel and traffic patterns. The research period extended from March 1990 to September 1991. The Zeeburger Tunnel crosses under the North Sea Canal, which cuts through Amsterdam in the east-west direction. North Sea Canal crossing points had been subject to growing congestion in recent years, with many drivers commuting from their homes north of the canal to workplaces south of the canal. Opening of the Zeeburger Tunnel provided a 25 percent increase in capacity across the North Sea Canal. The study included traffic counts, interviews with members of 12,000 households north of the North Sea Canal, and roadside origin-destination interviews with 50,000 road users crossing the canal. The study revealed that the opening of the Zeeburger Tunnel caused a 4.5 percent increase in automobile traffic across the North Sea Canal, broken down as follows: A 1.5 percent increase from route diversion, A 1.0 percent increase from diversion from transit, and A 2.0 percent increase from changes in destinations or travel frequency.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Notwithstanding the relatively small increase in total traffic due to the tunnel opening, a significant increase in peak-period traffic was found. In the 7 to 9 a.m. time period, the number of canal crossings increased by 16 percent, primarily as a result of drivers changing their travel times. Ruiter et al. (1979, 1980) used transportation planning models to estimate the effects on VMT of two highway improvement projects in California. The models used by Ruiter differed from those used in conventional travel forecasting in that trip generation rates were sensitive to travel times. However, land use patterns were fixed, so that changes in VMT associated with changes in land use patterns were not incorporated in the model outputs. The first project involved the construction of 5 mi of a new 8-lane freeway, which constituted a 0.855 percent increase in capacity in the study area. This increase in capacity was found to cause a 0.379 percent increase in VMT in the study area. Dividing the percent increase in VMT by the percent increase in capacity produces an estimated elasticity of VMT with respect to capacity of 0.4. The second project examined by Ruiter et al. involved widening a 12-mi section of freeway from 4 lanes to 6 or 8 lanes (depending on the location), which constituted a 0.647 percent increase in study area capacity. This increase in capacity was found to produce a slight decrease in VMT, with added VMT from new trips offset by reduced circuity of travel for existing trips. A key distinction between the two projects studied by Ruiter is that the first project was a new freeway that would provide significant time savings in both the peak and off-peak periods, whereas the second project was the widening of an existing freeway that would provide significant time savings in the peak period only. The primary effect on VMT of the second project was a shift in VMT from the off-peak to peak periods. Hansen et al. (1993) examined before-and-after traffic volumes for 18 California highway projects involving capacity additions to existing highways. They used pooled time series and cross-sectional data to estimate elasticities of traffic volumes with respect to highway capacity (i.e., the percentage increase in volumes divided by the percentage increase in capacity). For individual segments, the elasticities were found to increase somewhat over time. Elasticities of 0.3 to 0.4

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use were found during the first 10 years after the capacity increase. This means that if a segment's capacity is increased by 10 percent, traffic on that segment will increase by 3 to 4 percent during the first 10 years. After approximately 20 years, the elasticities were found to increase to 0.4 to 0.7. The authors noted an important limitation of the study of individual segments: only traffic levels on the improved segments were studied. They stated “ ... clearly, any additional traffic on the improved segment must also use other links on the roadway network as well. Further, a large proportion of the additional traffic may have diverted from other routes. These complement-substitute relationships between different links in a road network imply that if a change to one link has a substantial traffic impact on that link, other links are likely to be significantly affected as well” (Hansen et al. 1993, 3,4). Elasticities such as those developed by Ruiter et al. and Hansen et al. provide a simple means for summarizing study findings regarding the effects of increases in highway capacity on travel. Hansen et al. measured changes in capacity in terms of lane miles, and Ruiter et al. measured changes in capacity in terms of vehicle miles of capacity.1 One advantage of using the changes in lane miles or vehicle miles of capacity to represent improvements in capacity is that these measures can often be compiled for a given area directly from highway system inventories maintained by state departments of transportation. However, these measures also have a number of limitations that greatly affect the transferability of elasticities to other areas or capacity improvements. Most important, the amount of time savings produced by a given change in lane miles or vehicle miles of capacity is highly variable, depending on such factors as preexisting levels of congestion and bottlenecks. Consider, for example, a congested bridge that is a traffic bottleneck during peak periods. Widening the bridge could provide large peak-period time savings with a small increase in lane miles or vehicle miles of capacity. Conversely, adding lanes to a facility that is not currently congested will have a small effect on travel time, even though the addition may represent a significant increase in lane miles. In addition, the construction of new limited-access highways (with much higher free-flow speeds than the facilities they replace) will have travel time effects that are not well represented by the change in capacity. Finally, the use of elasticities must take into

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use account the types of traffic effects that are and are not reflected in the elasticities (i.e., the elasticities developed by Ruiter et al. represent the net effects on total highway system use, whereas the elasticities developed by Hansen et al. represent the effects on the improved facilities and include diversion from other facilities). A recently released report for the Department of Transport of the United Kingdom (SACTRA 1994) reviewed the evidence for the existence of induced traffic. As in many metropolitan areas in the United States, the Department of Transport uses transportation models that assume fixed trip patterns (but allow for the effect of general economic growth on traffic growth) in assessing new road projects or major highway capacity additions (SACTRA 1994, iv). The Standing Committee's review of case studies of major European highway projects, as well as of the Department of Transport's own monitoring studies of before-and-after traffic flows on road improvement projects, found that traffic increases on newly expanded road segments more than exceeded traffic reductions on unimproved segments. This finding provides evidence of induced traffic, that is, of growth in traffic beyond route shifts (SACTRA 1994, 80). However, the Standing Committee indicated that the studies are not helpful in identifying the components of this traffic growth (SACTRA 1994, 76, 77). It is not possible, for example, to distinguish changes in the time-of-day of travel or separate travel growth attributable to improved economic conditions from growth attributable to the road improvement itself, nor is it possible to rule out as a source of traffic growth broader shifts in travel routes than are captured by study control corridors and screenlines (SACTRA 1994, 76). The Standing Committee also reviewed the evidence for induced traffic using transportation models that allow demand to vary. Predicted estimates of induced traffic from major highway capacity additions in congested urban areas were found to be small when viewed at the network level; the effects were more significant in the corridors directly affected by the road projects (SACTRA 1994, 160). Because the scale of effects depends on the size of the study area modeled the scale of the project, and the behavioral responses modeled, among other factors, the Standing Committee noted the circumstances in which induced traffic is most likely to be large (SACTRA 1994, 169, 170):

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use When the network is operating, or is expected to operate, close to capacity, Where elasticity of demand with respect to travel cost is high, and Where implementation of a project causes large changes in travel costs. Two other areas of interest to this study were mentioned in the report. First, with respect to freight travel, the Standing Committee noted the limited studies of the effects of road improvements on the distribution of freight (SACTRA 1994, 158). The available research suggests that the impact of new road capacity on freight is likely to be greater where transport costs constitute a large share of the total distribution expenditures of a company (SACTRA 1994, 159). However, the researchers caution that the role of highway improvements should not be “exaggerated ” because other factors also have a considerable impact on distribution system costs (SACTRA 1994, 159). Second, new travel resulting from development induced by highway capacity additions is identified in the report as a major source of induced travel. However, the Standing Committee notes the considerable difficulty of separating development that can be attributed to the accessibility provided by the new or improved facility from development that would have occurred anyway because of other economic conditions (SACTRA 1994, 25). It also acknowledges the difficulty of distinguishing development that has simply been transferred from elsewhere in the region (thus resulting in a decline in traffic in those areas) from development that represents net new growth (and thus net new travel) in the region (SACTRA 1994, 25). AREAWIDE STUDIES A number of researchers have used data for entire metropolitan areas (or large districts within them) to obtain models that predict vehicle miles of travel within these areas as a function of transportation system supply. Ruiter et al. (1979, 2-34) summarized results from several of these studies in the form of elasticities (see Table B-1).

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use TABLE B-1 Estimated Elasticities of VMT with Respect to Transportation Supply Measures (Ruiter et al. 1979, 2-34) TRANSPORTATION SUPPLY MEASURE ELASTICITIES SOURCES Average highway speed +0.58, + 1.76 A.M. Voorhees & Assoc. (1971), Zahavi (1972) Total lane miles of highway +0.13, +0.15 Kassoff and Gendell (1972), Koppelman (1972) Lane miles of Interstate +0.0056 Mellman (1976) Lane miles of freeways +0.05 A.M. Voorhees & Assoc. (1971) Miles of rail transit service −0.033 Mellman (1976) Vehicle miles of transit service −0.09 EIC Corporation (1976) Seat miles of transit service −0.0098 A.M. Voorhees & Assoc. (1971) Fraction of driving surface on freeways +0.16 Koppelman (1970) For most of the supply measures, the elasticities are small, indicating small expected changes in areawide VMT as the supply measures change. The exception is average highway speed, with estimated elasticities of 0.58 and 1.76. In addition to the study of specific facilities discussed previously, Hansen et al. (1993) conducted an areawide analysis in which they compiled data on VMT, lane miles, population, density, personal income, and gasoline prices for 32 urban counties in California from 1973 to 1990. Pooled time series and cross-sectional data were used to estimate several VMT models. Results from the areawide studies were reported as elasticities of VMT with respect to lane miles. These elasticities were found to be 0.5 to 0.6, implying that a 10 percent increase in lane miles would result in a 5 to 6 percent increase in VMT. The authors noted a significant data limitation in conducting the areawide analysis: whereas data for VMT for state highways were available over a sufficient period to include significant temporal variation in lane miles, data for total VMT (including local roads) were available for a considerably shorter span of years. Consequently, the main focus of their study was on how changes in lane miles on state high-

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use ways affect traffic on state highways. However, to account for the possibility that the effect of increases in lane miles on state highways was merely to divert traffic from nonstate highways, the authors conducted some limited analyses using total VMT data; they tentatively concluded that the increases in traffic observed on state highways primarily represented new traffic and not diverted traffic. One potential problem, which was not discussed by the authors, is the possibility that estimates of the effects of changes in lane miles on VMT might have been affected by reclassification of nonstate highways as state highways or conversely. The authors discussed the problem of direction of causality in relating capacity increases and VMT. They noted that their analysis assumes that “road supply is the cause and traffic the effect, whereas in fact, traffic levels affect road supply as well. While we concede that the causality is bidirectional, we do not believe that this substantially affects our results. State and regional planning processes are subject to imperfect information, lumpiness of investment, fluctuations in costs and revenues, politically motivated allocation formulas, and other ‘exogenous' factors that significantly loosen the coupling between road supply and road traffic” (Hansen et al. 1993, 6-2). The regression equations developed by Hansen et al. show that, of all the factors affecting VMT growth, population growth, with an elasticity in the range of 0.7 to 0.8, is the most important (Hansen et al. 1993, 6-29). Hence, during the study period, growth in population contributed much more to the growth in VMT than did growth in lane miles. Other factors cited by the authors as affecting VMT were declining gasoline prices, increased two-worker commuting, and increases in per capita car ownership (Hansen et al. 1993, 6-31). TRAVEL TIME ELASTICITIES Several researchers have estimated highway travel time elasticities (defined as the percentage change in travel between two areas divided by the percentage change in travel time) Domencich et al. (1968) estimated the in-vehicle travel time elasticities of −0.82 for automobile work trips and −1.02 for automobile shopping trips. Their analysis used cross-sectional data on

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use zone-to-zone travel volumes, times, and costs from the Boston area. These elasticities overstate the systemwide effects of travel time improvements because only part of the observed increase in zone-to-zone travel is composed of completely new trips (i.e., some of the observed increase is from changes in trip destinations). Chan and Ou (1978) reported the travel time elasticity for automobile work trips as −0.4 for Louisville. Groenhout et al. [1986 (in Industry Commission 1993)] estimated the elasticity of automobile travel with respect to in-vehicle travel time as −0.17 for Sydney, Australia. Burright (1984) estimated the elasticity of vehicle miles with respect to travel time as −0.27 without land use changes and as −0.51 when the indirect effects of land use changes were taken into account. Numerous studies of travel time elasticities were also reviewed for the SACTRA report (1994). On the basis of these studies and calculations using the Department of Transport's own estimates of the cost of travel (i.e., direct fuel costs and travel time costs), the Standing Committee concluded that a travel time elasticity of −0.5 in the short term and −1.0 in the long term were reasonable estimates (SACTRA 1994, 45, 46). The long-term estimate, which implies that all of the travel time savings would be spent in additional travel, is high compared with studies reviewed for this and other recent reports (Dowling et al. 1994). These studies suggest that travel time elasticities are nearly always less than one. The Standing Committee notes that the higher estimate is consistent with the concept of stable travel time budgets promoted by Zahavi and others (SACTRA 1994, 40). The notion is based on empirical evidence that, despite differences in travel conditions and opportunities even across countries, travelers tend to spend the same amount of time, on average, in daily travel. According to this concept, savings in travel time and costs will be used for more travel. However, the Standing Committee itself points out (SACTRA 1994, 40) that the concept of constant travel time budgets has been the subject of considerable debate (Gunn 1981; Kitamura 1991, 24, 25), calling into question the notion that all travel time savings are spent in additional travel.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use The estimation and application of travel time elasticities is also subject to many practical problems, which are described in this report in Chapter 4. Notwithstanding these problems, travel time elasticities have been used to estimate potential induced traffic from highway capacity increases. In response to questions about the potential induced traffic effects of Westway, a highly controversial 4-mi Interstate segment proposed for the lower west side of Manhattan, project staff developed modifications to traffic forecasting software that allowed the direct application of travel time elasticities for individual pairs of traffic analysis zones. Specifically, zone-to-zone travel times in Manhattan with and without Westway were compared, and the number of trips between zones was adjusted on the basis of time savings. For example, with an elasticity of −0.25, a 10 percent travel time reduction between two zones from the new highway would result in a 2.5 percent increase in travel between the zones. Separate analyses were performed for a.m. peak, p.m. peak, and off-peak periods; however, no attempt was made to account explicitly for shifts of travelers among time periods or the substitution of longer trips for shorter trips. Thus, the analytical procedure can be regarded as a reasonable way of developing rough estimates of the induced traffic and associated impacts from highway improvements. The fact that travel time elasticities generally fall between 0.0 and −1.0 means that only part of the time savings resulting from highway improvements is used for additional travel. For example, with an assumed travel time elasticity of −0.5, a 10 percent decrease in travel time per trip will result in a 5 percent increase in the number of trips. Hence, total travel time (calculated as travel time per trip multiplied by the number of trips) will decrease. NOTE 1. For a highway segment, vehicle miles of capacity is calculated as the product of the segment length (in miles) and its capacity (in vehicles per hour). Vehicle miles of capacity is a more accurate measure of areawide capacity than lane miles because it accounts for the fact that highways with signalized intersections or stop signs have much less capacity per lane than freeways.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use REFERENCES ABBREVIATION SACTRA The Standing Advisory Committee on Trunk Road Assessment Bovy, P.H.L., A.L. Loos, and G.C. De Jong. 1992. Effects of the Opening of the Amsterdam Orbital Motorway. Final Report Phase I. Ministry of Transport and Public Works, Transportation and Traffic Research Division, Rotterdam, Netherlands, 83 pp. Burright, B.K. 1984. Cities and Travel. Garland Publishing, New York, N.Y. Chan, Y., and F.L. Ou. 1978. Tabulating Demand Elasticities for Urban Travel Forecasting. In Transportation Research Record 673, TRB, National Research Council, Washington, D.C., pp. 40–46. Domencich, T.A., G. Kraft, and J.P. Valette. 1968. Estimation of Urban Passenger Travel Behavior: An Economic Demand Model. In Highway Research Record 238, HRB, National Research Council, Washington, D.C., pp. 64–78. Dowling, R., S.B. Colman, and A. Chen. 1994. Effects of Increased Highway Capacity on Travel Behavior. Prepared for California Air Resources Board. Dowling Associates, Oakland, Calif., Oct. EIC Corporation. 1976. Refinement to the AEEP Fleet Model. Prepared for the Transportation Systems Center, Cambridge, Mass. Frye, F.F. 1964a. Redistribution of Traffic in the Dan Ryan Expressway Corridor. CATS Research News, Vol. 6, No. 3, June 26, pp. 6–14. Frye, F.F. 1964b. Eisenhower Expressway Study Area-1964. CATS Research News, Vol. 6, No. 4, June 24, pp. 7–13. Groenhout, R., D. Madan, and M. Ranjbar. 1986. Mode Choice for Urban Travellers in Sydney. Transport and Planning, Vol. 13, Part 8, pp. 52–62. Gunn, H.F. 1981. Travel Budgets: A Review of Evidence and Modelling Implications. Transportation Research, Vol. 15 A. No. 1. Hansen, M., D. Gillen, A. Dobbins, U. Huang, and M. Puvathingal. 1993. The Air Quality Impacts of Urban Highway Capacity Expansion: Traffic Generation and Land Use Change. UCB-ITS-RR-93-5. Institute of Transportation Studies, University of California, Berkeley, April. Holder, R.W., and V.G. Stover. 1972. An Evaluation of Induced Traffic on New Highway Facilities. Texas A&M University, College Station, March. Industry Commission. 1993. Appendix B: Determinants of Demand for Urban Travel. Urban Transport, Vol 2: Appendices. Australia, Oct. 14. Jorgensen, R.E. 1947. Influence of Expressways in Diverting Traffic from Alternate Routes and in Generating New Traffic. HRB Proc., Vol. 27, pp. 322–330.

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EXPANDING METROPOLITAN HIGHWAYS: Implications for Air Quality and Energy Use Kassoff, H., and D.S. Gendell. 1972. An Approach to Multiregional Urban Transportation Policy Planning . In Highway Research Record 348, HRB, National Research Council, Washington, D.C., pp. 76–93. Kitamura, R. 1991. The Effects of Added Transportation Capacity on Travel: A Review of Theoretical and Empirical Results. Proc., The Effects of Added Transportation Capacity, Bethesda, Md., pp. 21–37. Koppelman, F.S. 1970. A Model for Highway Needs Evaluation. In Highway Research Record 314, HRB, National Research Council, Washington, D.C., pp. 123–134. Koppelman, F.S. 1972. Preliminary Study of Development of a Macro Urban Travel Demand Model . Prepared for U.S. DOT, Assistant Secretary of Policy and International Affairs. Department of Civil Engineering, MIT, Cambridge, Mass, Dec. Lynch, J.T. 1955. Traffic Diversion to Toll Roads. Proceedings 702, American Society of Civil Engineers, June, Washington, D.C., pp. 1–27. Mellman, R.E. 1976. Aggregate Auto Travel Forecasting: State of the Art and Suggestions for Future Research. Transportation Systems Center, Cambridge, Mass, June. Pells, S.R. 1989. User Response to New Road Capacity: A Review of Published Evidence . Working Paper 283, Institute for Transport Studies, The University of Leeds, Yorkshire, England, Nov. Ruiter, E.R., W.R. Loudon, C.R. Kern, D.A. Bell, M.J. Rothenberg, and T.W. Austin. 1979. The Relationship of Changes in Urban Highway Supply to Vehicle Miles of Travel. Final Report (Preliminary Draft). Cambridge Systematics, Inc., Cambridge, Mass. ; JHK & Associates, Alexandria, Va, March. Ruiter, E.R., W.R. Loudon, C.R. Kern, D.A. Bell, M.J. Rothenberg, and T.W. Austin. 1980. The Vehicle-Miles of Travel-Urban Highway Supply Relationship. NCHRP Research Results Digest 127. TRB, National Research Council, Washington, D.C., Dec. SACTRA. 1994. Trunk Roads and the Generation of Traffic. Conducted for the Department of Transport, London, England, Dec. Alan M. Voorhees & Associates, Inc. 1971. A System Sensitive Approach for Forecasting Urbanized Area Travel Demands. FH-11-7546. FHWA, U.S. Department of Transportation, Dec. Zahavi, Y. 1972. Traffic Performance Evaluation of Road Networks by the Alpha-Relationship . Traffic Engineering and Control, Vol. 14, Nos. 5,6.