Agenda - Planning Commission - 01/31/2013 - Special

Home

TRAFFIC AND DENSITY Congestion and density are often tied together when examining the impacts of growth —the greater the collective density of an area, the greater number of cars on the road. This is true, but the actual relationship to congestion is quite difficult to measure. The entire science of transportation plan- ning constantly searches for the next best predictive tool to define this relationship. But if the goal is to prevent congestion, zoning ordinances and their density limits are not the best solutions. After all, some of the most congested roadways —commercial highway corridors —are notorious for being devoid of residential development at any density. The problem, then, is not the amount of density in any given area but the design of the road network. Planners are often fully aware that a network that funnels many small roads into a few major collectors and arterials is the true cause of congestion. Local densi- ties are seldom a contributing factor when regional traffic is diverted onto major high- ways. These common networks should be redesigned to provide more route options, such as grid networks, rather than propose limited density somewhere along the outer reaches of the highway. And when a solution does involve residential densities in some respect, that solution is often not in limiting density in each development but allowing more through urbanized infill development. After all, each city has a certain amount of market demand for new housing. If that de- mand is for 4,00o new homes in a given year, but zoning requires these homes to occupy no more than four units an acre, that leads to i,000 acres of development, with each house placed increasingly further away from desti- nations. As these houses are placed further away, their dependence on automobiles and limited road networks becomes greater. This is a prime example of how low and medium density (e.g., two to six units per acre) can exacerbate congestion. When viewed in light of the long history of sprawl development, density regulation to manage traffic congestion is neither a direct, effective solution for the problem or a sus- tainable practice when an area experiences demand for more growth. A zolz study of the Arizona Department of Transportation finds this very condition to be the source of many traffic issues today. The solution? More grid streets and higher density development of the sort proposed in both the Iowa City development and Mission Meridian South. This finding is supported by a careful analy- sis of four different areas of development. Each area features differing levels of devel- opment density and design, and the result is that the highest density areas featuring the best design actually perform better at mitigating congestion when compared to lower density areas. is often drafted to the detriment of the com- munity's character. In this respect, there is a fine balance between too much and too little parking. The more parking that a multifamily development is required to build, the larger the parking lots become, creating empty space along street frontages and creating an "island effect" where the multifamily building is often surrounded on all sides by more and COMPARATIVE CHARACTERISTICS AND PERFORMANCE OF THE FOUR STUDY AREAS Scottsdale Bell Road Central Avenue Tempe Land use Density High Low/Medium High Medium/High Mix Good/Very good Poor Fair/Good Good/Very good Design Good/Very good Poor Road network Alternate routes High Poor Good/Very good Good/Very good High Very good Manageable grid High Traffic congestion Midday Moderate Poor High Good/Very good Very high Moderate High Peak Moderate Severe Moderate High Transit Service/Servicability Good/Good Low/Poor Very good Good/Good Utilization Through traffic a Internal trip capture Work Good Moderate Moderate Low High Low Very good Good/Very good Moderate/High Moderate/High Moderate Moderate Nonwork Very High Average trip length Work Third shortest Nonwork Shortest Walkability Walk/bike trip rates Second highest High Longest Low Moderate/High Shortest Second Shortest Longest Third shortest Second Shortest Lowest Third highest Highest Q Summary Chart from Arizona Department of Transportation study "Land Use and Traffic Congestion," March 2012. PARKING AND DENSITY When Iowa City considered the proposal for a new, high -density residential develop- ment, opponents raised concerns about a potential parking shortage. This impact can often be very real, but the typical solution more parking. Such requirements often run counter to the established form of an area and add to the incompatibility issue. Recent publications and advances in parking technology (such as demand pric- ing for parking meters) indicate that better Q This multifamily development faces single-family homes on the other side of a highway. Poor design creates high degrees of separation between the neighboring areas. ZONINGPRACTICE 11.12 AMERICAN PLANNING ASSOCIATION I page 6