The Numbers Behind Des Moines Pavement

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

Every season, soil and housing claim on this site traces back to a public dataset, and this page gathers the main ones in one place. Weather comes from NOAA's 1991-2020 climate normals for the Des Moines International Airport station, USW00014933, which sits at latitude 41.53 and an elevation of 291.7 meters. Housing age and population come from the Census Bureau, and street and snow figures from the City of Des Moines and the Iowa Department of Transportation.

These are normals and survey estimates, not forecasts. A normal is a 30-year average, so any single winter can run warmer or colder, and American Community Survey figures carry margins of error. They are still the right basis for planning, because they describe what a driveway here should expect in a typical year. They also explain the timing advice in the clay and drainage guide.

Freeze-thaw days, month by month

The freeze-thaw figure used across this site is arithmetic on two published NOAA counts. One is the number of days a year the low reaches 32 degrees or colder; the other is the number of days the high never climbs above 32. A day in the first group but not the second is a day the surface froze and then thawed again. At the airport station the counts are 124.7 and 44.2, which leaves 80.5 crossing days in a normal year.

The monthly split shows where they land. December through February account for 43.0 of those days, March through May for 20.5 and September through November for 17.0. March and December tie at the top with 15.5 each, and the March cycles coincide with the start of the Clarion soils' March-to-June saturated season, when a thawing base carries the least load.

May and September each add 0.1 day with a low at or below 32 F. NOAA publishes these normals in tenths; the full-year row is the published annual normal.

Freeze dates, heat and rain

The freeze dates frame the working year. Sealer needs 50 degrees and rising, and the normal overnight low first clears 50 in May and falls back below it in October, so the reliable sealing window is shorter than the 182-day growing season between the median 32-degree freezes. Hot-mix paving can run a little longer at each end, since Iowa DOT allows thicker lifts at a 40-degree surface temperature.

Summer brings its own limits. Fresh sealer is soft on the hottest afternoons, and the station averages 18.4 days a year at 90 degrees or more, most of them in July. Rain is concentrated in late spring and early summer, with June the wettest month and May close behind, so those weeks carry the most risk of a washed-out sealing day.

Housing age in the city and four suburbs

House age is only a rough guide to pavement age, since drives get replaced, but it shows which problems dominate where. The city's stock is old: 26,067 units date from 1939 or earlier and another 14,483 from the 1950s. The four suburbs with pages on this site are far younger, and Johnston and Ankeny were mostly built after 1990.

Other suburbs show the same outward growth in their Census medians: 1960 in Windsor Heights, 1995 in Clive, 1998 in Altoona, 2002 in Pleasant Hill and Norwalk, 2009 in Grimes, and 2011 in Waukee and Bondurant.

American Community Survey 2020-2024 five-year estimates, tables B25035 and B25034; shares computed from the published counts.

Growth since 2010

The capital has held roughly steady while the suburbs filled in. Des Moines gained about 4 percent from 2010 to the July 2025 estimate, and Polk County about 20 percent. Ankeny grew by about 71 percent and Waukee more than doubled. Much of that growth arrived as new housing, and with it new driveways and lots: pavement that will need its first seal, its first crack filling and eventually its first overlay over the coming decades.

Census Bureau QuickFacts; change computed from the 2010 census count and the Vintage 2025 estimate.

Streets, salt and snow rules

City and state winter operations shape what reaches a driveway apron. The figures below come from the City of Des Moines and the Iowa Department of Transportation, and the rules apply inside Des Moines city limits; each suburb sets its own.

• 913 miles of roadway maintained by the city
• 43 percent of city streets rated poor or very poor in the city's own assessment
• Snow routes plowed once accumulation passes one inch; every home lies within four blocks of a snow route
• 13 trucks spray city-made brine of Kansas rock salt and Des Moines Water Works tap water ahead of storms
• Iowa DOT spreads about 200,000 tons of rock salt a year with roughly 900 snowplow trucks statewide
• Snow from driveways and lots may not go into the street or right-of-way; sidewalks must be cleared within 48 hours

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. NOAA NCEI, 1991-2020 annual and seasonal normals, Des Moines International Airport (USW00014933) — Values in tenths: ANN-TMIN-AVGNDS-LSTH032 1247 (124.7 days), ANN-TMAX-AVGNDS-LSTH032 442 (44.2), ANN-SNOW-NORMAL 353 (35.3 in), ANN-PRCP-NORMAL 3602 (36.02 in), ANN-TMIN-AVGNDS-LSTH000 111, ANN-TMAX-AVGNDS-GRTH090 184, ANN-PRCP-AVGNDS-GE100HI 85; freeze dates from the PRBLST and PRBFST fields; station name, latitude and elevation.
2. NOAA NCEI, 1991-2020 monthly normals: freeze counts, snowfall and precipitation (USW00014933) — Monthly days with lows and highs at or below 32 F, monthly snowfall and precipitation, used for the month-by-month freeze-thaw table and the March and June figures.
3. NOAA NCEI, 1991-2020 monthly normals: temperatures, hot days and heavy-rain days (USW00014933) — Normal monthly lows (May 52.2 F, September 55.2 F, October 43.0 F) and highs, days at or above 90 F by month, and days with an inch or more of rain.
4. Census Bureau, ACS 2020-2024 five-year, B25035 median year structure built, Des Moines city — Median year built 1961. The same table was read for West Des Moines (1994), Ankeny (2006), Urbandale (1992), Johnston (2004) and other Iowa places.
5. Census Bureau, ACS 2020-2024 five-year, B25034 year structure built, Des Moines city — 97,604 units; 26,067 built 1939 or earlier; 14,483 built in the 1950s. The same table was read for the four suburbs to compute the shares in the housing table.
6. Census Bureau QuickFacts, Ankeny city, Iowa — 2010 census 45,582, 2020 census 67,887, July 2025 estimate 77,833. QuickFacts pages for Des Moines, the other suburbs, Waukee and Polk County supplied the rest of the growth table.
7. City of Des Moines, Street Improvements — 43 percent of streets in poor or very poor condition; computer model and 20-year plan; Fleur Drive and Hubbell Avenue reconstruction.
8. City of Des Moines, Snow Removal — Rule against placing driveway and parking lot snow on the street or right-of-way, the 48-hour sidewalk rule, and snow parking restrictions.
9. Iowa DOT, Materials for Winter Storms — About 200,000 tons of rock salt used a year on Iowa highways; the plow truck count comes from the companion Equipment for Winter Storms page.