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.Figure 4.3, for example, presents a graphcomparing regional density with daily per capita VMT for the coun-try s largest 14 metropolitan regions.9For most of the cities shown in Figure 4.3, there is a fairly con-sistent relationship in which per capita VMT declines with regionaldensity.Los Angeles, however, stands as an exception.The only otherlarge metropolitan regions in the country with higher per capitaVMT, including Atlanta, Dallas, Houston, and Detroit, are all muchless dense than Los Angeles.For regions in which the level of densityapproaches that of Los Angeles, such as San Francisco, Washington,D.C., and New York, in turn, per capita VMT is much lower.We thussee a confluence of three density-related factors that, in combination,help to explain the severity of congestion in Los Angeles: (1) that con-gestion, as noted, is likely to rise with increased population density;(2) that Los Angeles is much denser at the regional level than its peersare; and (3) that Los Angeles exhibits a surprisingly high level of percapita VMT relative to its density.9Here again, we use the more recent density calculations based on data from Schrank andLomax (2007). 68 Moving Los Angeles: Short-Term Policy Options for Improving TransportationFigure 4.3Population Density and Daily Per Capita Vehicle-Miles Traveled in MajorMetropolitan Areas25DallasAtlantaHoustonDetroit Los Angeles20PhoenixSeattleBostonWashington, D.C.MiamiPhiladelphia15ChicagoNew York100 1,000 2,000 3,000 4,000 5,000 6,000Population per square mileSOURCE: Schrank and Lomax (2007).RAND MG748-4.3When attempting to diagnose the problem of congestion in LosAngeles, it is useful to consider why per capita VMT relative to den-sity is so high in comparison to other large metropolitan areas in theUnited States.We can suggest two possible reasons, although thereare likely other explanations as well.One possible explanation is thatthe network of fast, convenient transit services in the region is not asadvanced as one might expect in a region as dense as Los Angeles, inpart due to the challenges posed by the region s polycentric structure.Asecond reason is that the cost of traveling by car in Los Angeles, againrelative to density, is overly subsidized.We explore each of these argu-ments in turn.In considering transit as an alternative to driving, service withdedicated right-of-way offers the most compelling advantages, includ-ing higher operating speeds and greater travel-time reliability.This isDaily VMT per capita Diagnosing Congestion in Los Angeles 69the case with heavy rail (subways), commuter rail, and light rail.10 Bustransit can also be fast and effective.For this to be the case, however,it is typically necessary to provide some form of dedicated or restrictedright-of-way for bus service, such as bus-only lanes or shared bus/HOVlanes.Absent reserved right-of-way, buses will become mired in trafficcongestion just like automobiles do, precluding any potential travel-time advantages that might otherwise be achieved.11Our examination of higher-speed transit thus focuses on optionswith dedicated right-of-way including various forms of rail transitas well as exclusive or restricted12 bus lanes.Figure 4.4 compares thedensity of higher-speed transit options (represented as rail track milesplus busway miles per square mile in the urbanized area) with popula-tion density in each of the 14 largest metropolitan areas in the coun-try.In compiling the information about high-speed transit options,we began with data on the number of rail track miles in differentregions as reported by APTA (2007).Next, we added the mileage forall dedicated or restricted bus lanes that we could identify in majormetropolitan areas.In the greater L.A.region, we included the OrangeLine, the Harbor Transitway, the El Monte Busway, and bus service on10The speed advantage is most pronounced for fully grade-separated transit lines, includingsubways (e.g., Metro Red and Purple lines in Los Angeles) and many commuter-rail lines.Agreater proportion of light-rail transit lines (such as the Metro Gold, Green, and Blue lines inLos Angeles) share at-grade crossings with arterial roads and thus do not enjoy as much of aspeed advantage.11The Metro Rapid bus lines include a range of BRT features, such as signal prioritization,infrequent stops, and headway-based scheduling to make bus service more competitive (seethe discussion of BRT features in Appendix B25 for more details).While these features haveimproved bus-travel speeds and, in turn, led to increased patronage, the Rapid buses muststill share lanes with general traffic and thus are subject to congestion delays.As a result, theaverage daytime travel speed for Rapid buses traveling on the Wilshire corridor is just over11 mph (Jeff, 2007a).12In certain cases, we include shared bus and HOV lanes, provided that the HOV limit isset to preserve free-flowing traffic conditions.For example, the El Monte Busway allows bothbuses and carpools with three or more individuals.At one point, the HOV limit was reducedto two or more persons, but this quickly led to congested travel conditions in the lanes
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