Density, Diversity & Design

Relationships between built environments and accessibility

Source: Active accessibility: A review of operational measures of walking and cycling accessibility. David, Miguel, Mauro (2016)

The key elements of built environments features that affect accessibility metrics.

Pedestrians develop a close relationship with the built environment while walking. In practice, density is used as an implicit agent for overall accessibility. So, the denser place has more active accessibility nearby.

The close distance is an explicit measurement for the accessibility index. For the route characteristics, such as the condition of street connectivity are another explicit element for accessibility index.

The diversity which is measured by the land-use mix index is implicit measures for accessibility analysis. A place with a more mixed land-use or facilities there are more opportunities are generated.

Accessibility cannot be separated from the built environments that are closely linked with, and influence.

Density

Building Density

Neighborhood Density

Diversity

Building Diversity

Neighborhood Diversity

Distance

Building Location

Route Characteristics

Urban Fabric

Cervero’s Built Environment Variables of 3Ds, 1997 — the effect size for neighbourhood type

1.Density

population (population per developed acre); employment (employment per developed acre); accessibility to facilities (expressed in a gravity model form)

2.Diversity

Dissimilarity index (proportion of dissimilar land uses among hectare grid cells within a tract); entropy (mean entropy for land-use categories among hectare grid cells within a half-mile radius of each hectare grid cell within a tract); vertical mixture (proportion of commercial/retail parcels with more than one land-use category on the site)

Per developed acre intensities of land uses classified as — residential, commercial, office, industrial, institutional, parks and recreation; activity center mixture (1)entropy of commercial land-use categories computed across all activity centers within a zone (2) proportion of activity centers with more than one category of commercial-retail uses (3) proportion of activity centers with stores classified as — convenience, auto-oriented, entertainment/recreational, offices, institutional, supermarkets, service-oriented

Commercial intensities measured as per developed acre rates of convenience stores, retail services, supermarkets, eateries, entertainment and recreational uses, auto-oriented services, mixed parcels; proximities to commercial-retail uses (1) proportion of developed acres within ¼ mile of a convenience store, retail-service use (2) proportion of residential acres within ¼ mile of a convenience store, retail-service use

3.Design

Streets (1) predominant pattern (e.g. regular grid, curvilinear grid)(2) proportion of intersections that are four-ways (a proxy of grid pattern) (3) per developed acre rates of freeway miles within or abutting track, number of freeway under- and over-passes, number of blocks (a proxy for the grain of road net), number of dead ends and cul-de-sacs, (4) averages of arterial speed limits, street widths

Pedestrian and cycling provisions (1) proportion of blocks with sidewalks, planting strips; overhead street lights; quadrilateral (i.e. rectangular or square) shape; bicycle lanes; mid-block crossings, (2) proportion of intersections with; signalized controls, (3) an average of block length; sidewalk width; distance between overhead street light; slope; pedestrian green lights at signalized intersections, (4) bicycle lanes per developed acre

Site design: the proportion of commercial-retail and service parcels with off-street parking; off-street parking between the store and curb; on-street front or side parking; on-site drive-ins or drive-throughs