13  Reduce impacts of transportation on natural, cultural, and developed environments.

Reduce impacts of transportation construction, operations, and use on the natural, cultural, and developed environments.

13.1 Impervious surface in the metro area

The plots below illustrate the amount of pavement per county in the Twin Cities. Roads and paved surfaces comprised 11% of surface area in the metro area, compared to 3% for buildings (Host, Rampi, and Knight 2016).

Paving surfaces for roads, buildings, and parking lots increases surface temperatures. Impervious surfaces prevent water from filtering into the ground and trap heat near the ground. Dark impervious surfaces, like asphalt, tend to absorb more heat than lighter colored ones do. As a result, they trap the most heat.

A trend of increasing impervious surface is concerning given climate change. Minnesota is projected to experience large warm-season temperature increases (Angel et al. 2018), specifically with five to 15 more days per summer with a maximum temperature above 95°F by mid-century 2041 - 2070 (Pryor et al. 2014). The Twin Cities region may have over 50 days with temperatures over 90 degrees by 2050, as compared to about 13 days on average today (Notaro, Bennington, and Lofgren 2015).

To learn more about how extreme heat and impervious surfaces relate, see Section 3.2.

Figure 13.1: Percent of each county covered by a paved surface parking lot

Figure 13.2 shows the proportion of each county covered by paved road lanes 1.

Figure 13.2: Percent of each county covered by paved road lanes.

  1. Lane miles are converted to area by using a width of 11 feet, in accordance with (Minnesota Administrative Rules: Minimum Design Standards, Urban; New or Reconstruction Projects 2017). This may be an underestimate of the existing lane area because this doesn’t include road shoulders or account for wider roads↩︎