LandUse andtrafficcongestion FinalReport618 March2012 Preparedby: J.RichardKuzmyak TransportationConsultant,LLC SilverSpring,Maryland InAssociationwith: CaliperCorporation Newton,Massachusetts and PolyTechCorporation Surprise,Arizona Preparedfor: ArizonaDepartmentofTransportation incooperationwith U.S.DepartmentofTransportation FederalHighwayAdministration 140 of 226
EXECUTIVESUMMARY The purpose of this project was to analyze and interpret the relationship between higherdensity development and traffic congestion. Governments have expressed increased interest in the possible benefits of compact, mixed land use referred to in many circles as smart growth to reduce auto dependency and use. If true, this finding could be of significance in planning solutions to a host of transportation system investment, performance, and impact issues. Before considering any type of formal policy position in relation to land use, the Arizona Department of Transportation (ADOT) is expanding its understanding of the relationships between land use development patterns and transportation. Among ADOT s key questions are: Does higher-density development reduce auto use, to what extent, and in response to what factors? Does higher-density development also generate higher levels of traffic congestion simply due to the higher concentration of activity? Do Arizonans know about smart growth, and what are their perceptions of its impacts and desirability? The research study that is summarized in this report was commissioned to address these specific issues. It involved a national-scale review of research and evidence on transportation and land use relationships; detailed local analysis of these relationships using data from metropolitan Phoenix; and a survey of officials in Arizona s metropolitan areas about their perceptions of land use/transportation, how higher-density development is viewed, and whether there would be receptiveness for compact, mixed-use approaches regionally and in their own area. The findings of this study confirm the benefits of better land use. In its assessment of a prodigious volume of research on this topic, the project s literature review was able to highlight the following findings: Density and Vehicle Miles Traveled Using residential density as a primary indicator of concentrated land use, a variety of studies have shown that households in higher-density (i.e., more urban) settings tend to own fewer vehicles, drive less, walk and take transit more often, and generate one-half to one-third of the daily vehicle miles traveled (VMT) of their suburban counterparts. Beyond Density: Research has found that the effects of land use on travel behavior are rooted in factors beyond simple density. Also important are related factors such as mix of uses, auto- vs. pedestrian-oriented design, and regional accessibility enhanced by multiple travel choices (especially transit). These characteristics of density, diversity, design, and destinations are commonly referred to as the 4Ds. Travel Purpose: Work travel, which is associated with peak period congestion, generally garners most of the attention in transportation planning and policy deliberations. Indeed, where compact land use is focused around high-quality 1 141 of 226
regional transit at both the origin and destination of a journey commuters will use transit in large numbers because of its convenience. However, the travel market that may be most influenced by compact mixed-land use is nonwork travel, which accounts for as much as 80 percent of routine household travel and has been the fastest-growing segment since the 1980s. This relationship/trend can be directly linked to land use, recognizing that in conventional suburban areas almost all household needs shopping, transporting children, personal business, social, and recreation require private vehicle travel. Areas where residents live in older, mixed-use communities with nearby services and restaurants show a much greater concentration of travel to local destinations including walking, biking, or short car trips despite a daily commute that may well be a long distance solo-driver trip. Market Forces: Critics of smart growth approaches to land use maintain that it is a planner s notion that does not reflect market realities. However, real estate industry experts assert that the reason more compact, mixed-use development has not occurred has to do with restrictive local zoning codes or traffic level of service standards, and not because of market demand, which is gauged as twice as high as current build rates. This is borne out by visual preference surveys that show a general preference for older (pre-world War II) suburban development patterns, which are more compact and walkable, and foster more social interaction between residents. To ascertain the validity of these research findings in the Arizona environment, researchers performed a number of detailed studies using local data and both existing planning tools as well as some new ones developed specially for analysis of the role of land use. These analyses were focused on the Phoenix metropolitan area and were performed using data, modeling tools, and staff support of the Maricopa Association of Governments (MAG). Conventional four-step transportation planning models are unable to account for important differences in land use as represented by the 4Ds. The influence of land use is most relevant at the level of the individual traveler and what they can walk to within ¼ to ½ mile at either origin or destination. Four-step models operate at a traffic analysis zone (TAZ) level of aggregation, which is generally much too coarse for discerning land use differences. For this reason, this genre of models also does not deal directly with nonmotorized trips such as biking or walking, which are a critical element in compact mixed use designs. Using data from MAG s 2001 regional household travel survey supplemented with information from its travel model and geographic information systems (GIS) databases, researchers developed a set of regression models to quantify the relationships between travel behavior, traveler demographic characteristics, and measures of the 4Ds. These models show the effect of the 4Ds of land use on both household vehicle ownership and on household VMT. Residential density, land use mix, walk opportunities, and regional transit accessibility to jobs were the variables used to represent the 4Ds. Negative signs on the coefficients for these variables indicate that as each of the land use variables 2 142 of 226
increases, vehicle ownership and VMT rates decline proportionately. Vehicle ownership is an important determinant of travel in the VMT models, so when it is reduced in relation to better land use, its effect is compounded by also acting to reduce VMT. The MAG region was divided into 17 jurisdictional areas and the household travel survey database used to explore differences in travel in relation to these key land use factors. Higher-density and more mixed-use areas such as South Scottsdale, Tempe, and East Phoenix were found to behave significantly differently from lower- density/less mixeduse areas like Glendale, Gilbert, and North Scottsdale. Residential density for the more compact areas ranged from 6.14 to 6.94 households per acre vs. 2.86 to 3.61 households for the lower-density group. These higher-density areas also had better mix (0.53 vs. 0.30 value on a 0 to 1.0 entropy index scale); more retail and service opportunities within walking distance (42.4 vs. 15.4); and considerably more jobs accessible by transit (59,000 vs. 27,000). The implications of these differences may be seen in various travel measures, including: Vehicle Ownership: 1.55 vs. 1.92. Average Trip Lengths: 7.4 vs. 10.7 miles for home-based work trips; 2.7 vs. 4.3 for home-based shopping trips; 4.4 vs. 5.2 for home-based other trips; and 4.6 vs. 5.3 for nonhome-based trips. Per Capita VMT: 10.5 miles per day vs. 15.4 miles per day. The 4Ds models were subsequently used to investigate the potential impact of improved land use characteristics in each of the 17 areas. To do this, average residential densities were raised to 10 households per acre (vs. on the order of two to four in most places), land use mix was brought to the ideal entropy index value of 1.0, the number of walk opportunities was increased to 100 in all places, and regional transit accessibility was raised to somewhere between the current minimum and maximum for the respective area. This resulted in estimates of VMT reduction of 20 percent to 45 percent, with an average overall of 25 percent. Having reasonably demonstrated that areas in Phoenix with higher density generated less vehicle travel per capita than lower-density areas, the second hypothesis investigated was whether a higher concentration of activity would also lead to localized traffic congestion. A sample of four urban corridors was selected for detailed study also in the Phoenix area based on information from local and regional officials that these areas were perceived to have major traffic congestion issues: Scottsdale Road between Thomas Road and Chaparral Road in the older, southern part of Scottsdale; Central Avenue north of downtown Phoenix, between McDowell Road and Camelback Road; the Mill Avenue and Apache Boulevard corridor through Tempe; and West Bell Road in the northwest part of the region, connecting the central valley with the newer communities of Peoria, Glendale, and Surprise. The objective was to examine the interplay between the intense development patterns in these areas and the condition of traffic on the street and road network. Researchers performed the following assessments: 3 143 of 226
Density: Three of the areas south Scottsdale, Central Avenue, and Tempe exhibited some of the highest development densities in the region while Bell Road served an area of intense activity spread over a large area of moderate to low density. Composition: The Scottsdale, Central Avenue, and Tempe areas also had a high level of mix in their land uses, while Bell Road was heavily residential. The overall jobs-to-housing ratio in the Bell Road area was only 0.49 compared to 1.42 in Scottsdale, 2.30 in Tempe, and 5.60 in the Central Avenue corridor. Retail jobs per household (a measure of access to local services) was not quite as skewed, but Bell Road s ratio of 0.31 was still only about half of the 0.56 to 0.65 level found in the other three areas. Road Network: Each area is served by the one mile arterial super grid, with no area having a freeway closer than two miles from its center. However, a major distinction occurs in the secondary road system, with Central Avenue and Scottsdale having a rich network of secondary streets on one-eighth mile spacing. Tempe s secondary grid is not quite as fine but is still much better than the Bell Road corridor, which has little secondary road system beyond subdivision networks. Transit: Central Avenue and Tempe are well-served by the regional bus system and are also connected by the region s inaugural light rail line (not operational at the time of the analysis). Scottsdale is moderately served by transit, while Bell Road has only park-and-ride bus service. Transit accounts for about 6 percent of all internal trips in Scottsdale, and between 3 percent and 6 percent of external trips. In the Central Avenue corridor, about 8 percent of internal trips and about 7 percent of external trips are made by transit, while in Tempe about 3 percent of internal trips and 5 percent to 10 percent of external trips are by transit. In contrast, less than 1 percent of all trips in the Bell Road corridor involve transit. Traffic Congestion: Interestingly, traffic congestion levels were much lower in the Scottsdale Road and Central Avenue corridors than in the Bell Road corridor. Volume-to-capacity (V/C) ratios in both Scottsdale and Central Avenue were in the 0.8 to 0.9 range in the PM peak period compared to 1.6 to almost 2.0 along Bell Road. Tempe fell predictably in between given its less-articulated secondary road network, with V/C ratios in the neighborhood of 1.0. Tempe also employs traffic-calming strategies on its secondary road network to discourage cut-through traffic, which pushes traffic onto major arterials. Through Traffic: Traffic volumes in each of the four areas are affected by through travel (no trip end within the defined area). Central Avenue, Bell Road, and Apache Boulevard in Tempe all had rates of through travel that accounted for about half of peak period traffic volumes. Without this through traffic movement, Central Avenue and Tempe would be relatively uncongested, though Bell Road would still be congested from its internal volume. Scottsdale s rate of through traffic on the measured links was much less about 22 percent to 28 percent probably due to the design of the local grid, which encourages through travelers to use peripheral streets. 4 144 of 226
These findings tended to corroborate responses elicited from participants in the project s survey of officials. For this survey, which was conducted early in the project, researchers distributed 423 questionnaires and received 134 responses from a diverse list of elected officials, planning and zoning officials, transportation planners, and members of other relevant disciplines in the Phoenix, Tucson, and Flagstaff metropolitan areas. Some of the key discoveries in this investigation are given below: Traffic Congestion Concerns: While important, traffic congestion was rated as less a factor in project review than were issues of compatibility with adopted plans and impact on surrounding neighborhoods and businesses. Familiarity: Most officials were familiar with mixed-use concepts, had been involved in the review of these concepts, and had even encouraged submission of such projects. Transportation Impacts: The overwhelming majority of officials responding believed that compact, mixed-use development would increase transit use and nonmotorized travel, though only about one-third felt unequivocally that it would lead to less traffic congestion. (Most were unsure.) Desirability: The great majority believed that the region would benefit from more mixed-use centers and corridors, focusing employment in centers and corridors, and building more mixed-use communities. About 80 percent believed that their own community would support compact, mixed-use development. Residential/retail and office/retail mixed use were the most highly rated combinations. These findings suggest an opportunity to advance the dialogue on and support for compact, mixed-use development in Arizona s metropolitan areas. Among the initiatives that might be considered are the following: Education: There is a need to better inform the public, the business community, and officials about the nature and benefits of compact, mixed use. Themes developed in this project can serve as educational messages. Better Analysis Tools: Local planners and planning commissions are still using traditional traffic engineering approaches to assess the impact of development projects. By looking only at traffic congestion levels on adjacent links, ignoring through travel, and failing to account for the efficiencies of mixed-use development on lower vehicle trip rates and VMT, progressive projects are likely to be rejected or unreasonably downsized. The metropolitan planning organizations should take steps to add 4D enhancements to their existing tools. Visioning and Plan Overhauls: Existing long-range or comprehensive plans may be silent or devoid of a position on compact, mixed-use development. Regional or local targeted visioning exercises can raise visibility and understanding of the issues, leading to greater acceptance and support in updated plans. Incentives: Adoption of compact, mixed-use development approaches can be encouraged in various ways. Grant monies and/or technical assistance can be offered to support studies or demonstration projects. Several states prioritize state program or grant funding based on demonstrated steps by a jurisdiction to embrace and incorporate key elements in their plans, codes, or procedures. 5 145 of 226
Supportive Infrastructure: A key incentive in its own right, local land use choices can be influenced by the manner in which transportation resources are distributed. Priorities can be placed on investments that will most contribute to concentrated land use policies such as transit investments, local street and sidewalk infrastructure, or rehab/upgrade of facilities in older developed areas. 6 146 of 226