On June 25, the Board of the San Diego Association of Governments approved the MXD method as the preferred means of adjusting trip generation estimates to account for the effects of smart growth.  The MXD method will complement the SANDAG Traffic Generators handbook as the standard for traffic studies within the region’s cities and counties.  SANDAG is one of the only regions within the US which has developed its own data and locally-validated methods for performing traffic generation analysis.  Most rely on the national data distributed by the Institute of Transportation Engineers (ITE) in their multi-edition report Trip Generation.

The MXD method was developed by Fehr & Peers and a research team for the US EPA through an analysis of about 240 mixed use development sites throughout the US.  In its study for SANDAG, Fehr & Peers validated the method by comparing its estimates to actual traffic counts at six smart growth developments, including Transit Oriented Development (TOD) sites in the San Diego region.  This validation supplements validation that Fehr & Peers had already performed at other sites in California, Florida, Texas and Georgia.

The MXD method is also under review by ITE as a possible supplement in an upcoming release in its Trip Generation Handbook and is undergoing evaluation by panels of experts and practitioners throughout California as part of a Caltrans/ UC Davis study to assess its acceptability for use in CEQA studies throughout the state.

Key Fehr & Peers staff involved in the SANDAG effort were: Rick Lee, Mark Feldman, Chris Gray, McKenzie Watten and Lisa Levasseur.

For more information on the MXD method, click here.

On June 25, the Board of the San Diego Association of Governments approved the MXD method as the preferred means of adjusting trip generation estimates to account for the effects of smart growth.  The MXD method will complement the SANDAG Traffic Generators handbook as the standard for traffic studies within the region’s cities and counties.  SANDAG is one of the only regions within the US which has developed its own data and locally-validated methods for performing traffic generation analysis.  Most rely on the national data distributed by the Institute of Transportation Engineers (ITE) in their multi-edition report Trip Generation.

The MXD method was developed by Fehr & Peers and a research team for the US EPA through an analysis of about 240 mixed use development sites throughout the US.  In its study for SANDAG, Fehr & Peers validated the method by comparing its estimates to actual traffic counts at six smart growth developments, including Transit Oriented Development (TOD) sites in the San Diego region.  This validation supplements validation that Fehr & Peers had already performed at other sites in California, Florida, Texas and Georgia.

The MXD method is also under review by ITE as a possible supplement in an upcoming release in its Trip Generation Handbook and is undergoing evaluation by panels of experts and practitioners throughout California as part of a Caltrans/ UC Davis study to assess its acceptability for use in CEQA studies throughout the state.

Key Fehr & Peers staff involved in the SANDAG effort were: Rick Lee, Mark Feldman, Chris Gray, McKenzie Watten and Lisa Levasseur.

For more information on the MXD method, click here.

By Jerry Walters

This is the third in a series of reviews of recent studies on transportation, land use and climate change.  The first two reviews addressed:

• Moving Cooler — by Cambridge Systematics for ULI, EPA, USDOT, et al
• Driving and the Built Environment – by a group of academics and national experts for TRB.

Each review compared the study findings with those of Growing Cooler – The Evidence on Urban Development and Climate Change, a 2008 ULI book co-authored by Fehr & Peers.

This third installment reviews:

• Travel Behavior, Residential Preference, and Urban Design: A Multi-Disciplinary National Analysis, by University of North Carolina, September 2009.

This report states in its summary and conclusions that Neo-Traditional Developments (NTD) generate more trips than typical suburban development. 

It is a very ambitious study that involved identifying 17 cases of paired neighborhoods, each within the same community, and comparing the neighborhood designs and travel behavior between members of each pair. The 17 communities included Carlsbad and Chula Vista in CA, Clackamas OR, and Colorado Springs, Longmont and Fort Collins CO as well as cities in Texas, Illinois and eight in the southeastern US.  Within each city, they measured and compared the two neighborhoods in terms of design (including the 5D’s of density, mix, urban design, infill vs greenfield, transit vs no transit) and they surveyed residents on their daily trip making.  To quote their stated findings:

“We found that residents of NTDs neighborhoods make more trips, more car trips, more non-motorized trips, and more trips internal to their neighborhood than residents of typical suburban neighborhoods. We found no difference in vehicle mileage, and thereby conclude that trips taken by NTD residents tend to be shorter in length than trips taken by their suburban counterparts. Furthermore, we did not find a statistical difference between neighborhood type residents in the frequency of external trips. This suggests that the difference in overall trips detected is the result of greater internal trip capture by the NTDs”.

However, careful read of the report indicates a very mixed message at best.  Among my observations:

• In most of the pairs there is very little difference between the two neighborhoods.  In some cases the use mix was better in the “suburban” neighborhood than the NTD, in others aspect of the suburban street connectivity were better than the NTD, and in others the differences even in density were too close to matter.  By my assessment, only four of the neighborhoods were significantly different from their mates, eight were only moderately different from their mates, and in five cases the differences were negligible. 
• By their nature, both members of each pair have the same transit service and both members of each pair were either greenfield or infill locations.  So the distinctions with respect to two of the primary determinants of trip reduction were nil.
• In the 17 total, only four of the pairs were infill and only nine had transit service.
• All of the neighborhoods, both NTD and suburban, were entirely single family residences.  On average across all of the neighborhoods, about 20% to 25% of the residents are retired. This may suggest that some of the pairs, especially in the Southeast, cater to retirees and are less representative of the full-spectrum developments we usually study.
• In spite of heroic efforts to survey household trip making, the study reports the reliability of its trip-making estimates at only 51%.

Finally, in spite of the bold statement in the report’s summary, Table 11 which contains a comparison of average trip making for the group of NTD versus suburban indicates that the survey means for NTD exhibit about:

• 12% lower VMT than suburban
• 5% lower vehicle trips than suburban
• 20% higher internal trips than suburban
• 120% higher non-motorized travel than suburban

They did construct models from their data and attempted to parse the differences to a more specific set of individual paired comparisons that may have lead them to their summary conclusions, but bear in mind that their travel survey was only 51% reliable, and only 4 of their 17 individual pairs had notable differences from one another with respect to density, diversity or design, and none had differences with respect to destination accessibility or transit.  It seems questionable that one would want to parse such data too finely. 

While not directly comparable to this study, others (including some of our own research) are finding that those who reside in remote locations tend to combine their trips more than those closer-in with all of their destinations nearby.  Trip chaining can result in lower vehicle trip generation for remote development, although household VMT is still considerably higher than for infill, mixed and transit-oriented development.

By Jerry Walters

Several new reports on the subject of transportation, land use and climate interactions, reach findings related to and/or directly refer to the findings of Growing Cooler- The Evidence on Urban Development and Climate Change, a 2008 ULI book co-authored by Fehr & Peers. This second of three posts will clarify the misconceptions and key differences between Growing Cooler and the most prominent of these studies:

• Last week: Moving Cooler – by Cambridge Systematics for ULI, EPA, US DOT, et al
• This week: Driving and the Built Environment – by a group of academics and national experts for TRB and the National Research Council.
• Next week: Travel Behavior, Residential Preference, and Urban Design – by the University of North Carolina

Driving and the Built Environment

This National Research Council (NRC) report finds lower VMT reduction resulting from land use strategies than did Growing Cooler and than were adopted into Moving Cooler. It estimates that the potential reductions in inter-urban passenger travel resulting from land use shifts and complementary transportation would be in the range of no greater than 8 to 11 percent by 2050, while Growing Cooler estimates the likely range to be between 12 and 18 percent.

The authors of Growing Cooler believe that the lower NRC estimate is the result of several questionable assumptions:

· The NRC study does not take into consideration the effects of more compact future commercial development and redevelopment, it only examines density increases related to residential growth,

· NRC assumes very, very slow redevelopment of residential properties, equivalent to about 500-year life-cycle for housing stock, compared to 170-year life-cycle projections that informed other studies such as Growing Cooler,

· The NRC analysis considered the effects of development density on VMT reductions but not the additional 4D effects of diversity (mixed use), design (walkability and connectively), destination accessibility (infill vs. spread sites), and development distance to core transit,

· The NRC study does not consider the synergistic effects that infill and mixed-use development has on its neighboring land uses, which can occur if it fills needs for complementary land use types. This may result from adding services and entertainment to homogeneous residential areas, or adding housing near pre-existing jobs or retail, or adding a more connected and amenable pedestrian environment to what may have previously been a gray-field or brownfield. It may also result from creating critical mass that generates additional transit investment in the area,

· Also, by working with national averages, the NRC study uses very broad averages of development form, unlikely to register on the benefits derived at a neighborhood or community scale. As reported the study works with average existing residential densities of only 1.7 to 2.9 dwelling units per acre, and then assumes that new development will only occur at densities of 1 DU per acre. As a result, their estimates of VMT reductions have little in common with the types of reductions likely to correspond with the local effects of compact, mixed use development on the vast amount of travel that takes place within neighborhoods and within communities.

In conclusion, the Growing Cooler authors believe that their own estimates represent a fully achievable estimate of VMT and GHG reduction.

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Coming up next…

- I will review UNC’s Travel Behavior, Residential Preference, and Urban Design: A Multi-Disciplinary National Analysis, which states: “We found that residents of neo-traditional developments make more car trips … than residents of typical suburban neighborhoods… We found no difference in vehicle mileage.”