College of Architecture and Planning
2 Does That Little Strip by the Sidewalk Cool Me Down?
Evan Klansnic and Alexandra G. Ponette-González
Faculty Mentor: Alexandra G. Ponette-González (City & Metropolitan Planning, Natural History Museum of Utah, University of Utah)
Abstract
Park strips, the narrow section of land between the sidewalk and the curb, are an important component of land cover within cities. These strips likely play an important role in modulating personal heat exposure within street environments. In this study, we mapped park strip cover along a 3.25 km section of West North Temple in Salt Lake City and categorized areas as grass, gravel, bare, mulch, shrub and no park strip. We walked this route on six summer afternoons (4:00p.m. to 6:00p.m.) from 06/17/25 to 06/28/25. A low-cost wearable temperature and humidity sensor recorded heat index every two seconds (n=4,920 observations) and each heat index record was matched in ArcGIS Pro to the nearby park strip cover type, as well as to a canopy/non-canopy category derived from the National Land Cover Database canopy raster.
Heat index varied by < 1°C among the six park strip cover types, with a range of 28.4 °C to 29.3 °C across all observations. This included park strip cover segments classified as shaded versus unshaded, where the differences never exceeded 1 °C. By contrast, intra- route variation in heat index within the two-hour sample window had a 2.7 – 3.3 °C range.
We did not detect differences in heat index among park strip cover types in this study, a pattern which may be due to the measurement method (mobile) or the relative influence of other factors such as intra-route variation, park strip characteristics (e.g., width), or surrounding urban form. Therefore, we suggest that future work employ fixed measurements of surface and radiant temperature on individual park strip cover types to assess how park strip cover affects pedestrians and the surrounding microclimate. Additional interventions such as tree planting and installation of permanent shade structures that allow more direct protection from the sun in this area could also be considered alongside park strip management.
Introduction
Salt Lake City (SLC) is warming rapidly from climate change and an intensive urban heat island effect (Chapman et al., 2017). Pedestrian heat stress is heightened along wide, asphalt-dominated corridors that absorb and reradiate solar energy throughout the day. Park strips, the narrow sections of land between the sidewalk and street, are very common within U.S. cities and widely range in surface material: grass, gravel, mulch, bare soil, shrub beds, and in cases no park strip at all.
Vegetated ground covers can cool the air via evapotranspiration (Qiu et al., 2013), and tree canopies can attenuate short-wave radiation. Yet, empirical evidence for cooling at pedestrian height is mixed, especially where strips are less than two meters wide (Shashua-Bar et al., 2011; Kim et al., 2018). Sidewalk-scale studies in Texas report air temperature reductions of 3.1-3.7 °C where grass replaces concrete, while other work points to a mix of overhead shade and less heat-absorbent surface material as the dominant driver of reduced pedestrian heat stress (Kim et al., 2018). Recent mobile-sensing research further highlights the large and dynamic variation introduced by daily weather (Gallacher & Boehnke, 2025).
Due to the influence of these varied factors, including vegetated ground cover, tree canopies and the interactions between the two, planners need clear guidance on whether changing park strip cover within cities can meaningfully improve pedestrian heat stress in hot, arid cities like SLC.
This study seeks to fill this gap by combining park strip cover mapping with mobile measurements of heat index, a commonly used indicator of heat stress that combines air temperature and relative humidity to better represent the way the human body perceives heat. Our objectives were to: (i) quantify afternoon heat index for six common park-strip covers along a 3.25 km section of West North Temple, a very busy corridor between the SLC Airport and Downtown, (ii) compare heat index in canopied versus uncanopied conditions for each park strip cover type; and (iii) evaluate whether park strip material or overhead canopy had a statistically significant influence on pedestrian heat index.
Methods
DATA
Data collection was conducted along a 3.25 km section of West North Temple, a major commuting corridor linking Salt Lake City International Airport with downtown (Figure 1). High resolution aerial imagery supplied within ArcGIS Pro coupled with field mapping of the route was used to classify and then digitize every continuous section of park strip cover as grass, gravel, bare, soil, mulch, shrub, or no strip. If a segment contained multiple surface materials, it was assigned to whichever cover occupied > 50% of its length. To identify potential overhead shade, the 2024 National Land Cover Database 30-meter tree canopy raster was overlain onto the study area.
MOBILE MONITORING
Six afternoon walks were completed between 17 June and 28 June 2025, every Tuesday, Thursday and Saturday between 4:00 and 6:00 PM MST, a period when pedestrian traffic is heightened and atmospheric stability maximizes heat stress. The walker maintained their own walking pace to reflect the variability of commuter pace. A Kestrel D3FW recorded air temperature and relative humidity every 2 seconds. The sensor was suspended on the bottom strap of a backpack to allow proper airflow and reduce interference from the backpack itself (Figure 2). An AirBeam3 particulate matter monitor provided GPS tracking via Bluetooth every 1 second. This sensor was attached to the upper strap of the backpack (Figure 2).
DATA PROCESSING and ANALYSIS
Raw Kestrel and AirBeam files were time-synced and merged in Python (pandas 2.2). Heat index (HI, °C) was derived by the Kestrel D3FW from temperature and relative humidity measurements. In ArcGIS Pro, points whose coordinates overlaid driveways or road surfaces were deleted to isolate sidewalk conditions. A point-near-polygon join then assigned each remaining data point to the nearest park-strip class, and a point-in-raster overlay tagged canopy status (present/absent) from the 2024 NLCD tree-canopy layer. For each of the six walks, we computed mean heat index for every cover × shade combination (12 values per day). These daily means served two purposes: (i) they were averaged across the six days to produce the 12 grand means shown in Figure 3, and (ii) they provided six replicate observations per factor level (72 total) for statistical testing. A two-way fixed-effects ANOVA tested main effects (park strip cover, canopy) and their interaction on the daily means using statsmodels 0.14 (anova_lm). Route variability in temperature was characterized by plotting each walk’s maximum, minimum, and range (Figure 4).
Results
Across the six afternoon walks, we recorded 4920 valid heat index data points. When categorized by park strip cover and canopy cover, the average afternoon heat index across all days ranged from 28.4 °C to 29.3 °C, a tight spread of < 1 °C across all six park strip cover types (Figure 3, solid bars). Bare strips showed the lowest mean heat index in full sun (28.4 °C), whereas gravel strips were the warmest (29.1 °C). Introducing overhead tree canopy did not significantly change park strip cover heat index differences. Under canopy, gravel cooled by 0.3 °C and bare soil warmed by 0.9 °C relative to park strips without canopy cover (Figure 3, hatched bars). The four remaining covers (grass, shrub mulch, and no strip) clustered tightly around 28.7 – 29.1°C regardless of shade. Sample sizes for each category were uneven, representing a range from 139 to 815 individual heat index points. A two-way ANOVA applied to the 72 individual daily means (12 cover x 2 canopy cover designations x 6 days) detected no significant main effects of park strip cover type, canopy status, or their interaction (all p ≥ 0.95).
By contrast, intra-route variability had a much larger range than any park strip cover type or area differing in canopy status. Within each two hour walk, heat index varied by 2.7-3.3 °C along the route, roughly three times the maximum difference found among park strip covers or canopy categories (Figure 4). The hottest day (06/19) had an average temperature of 35.4 °C yet showed a slightly smaller intra route range from 34.2 °C to 36.9 °C (2.7 °C range), whereas cooler days (06/21, 21.95 °C) showed sharper rises and falls from 20.7 °C to 23.8 °C (3.1 °C range).
Discussion
Contrary to expectation, we did not find a significant difference in pedestrian exposure to heat stress along our route. The effects of park strip cover and canopy cover differences (< 1 °C) on heat index were likely masked by other factors along the route. First, the corridor’s asphalt and concrete act as a potent heat source. Controlled experiments in a hot-arid courtyard showed that a fully paved, unshaded surface remained “uncomfortable throughout the daytimes hours,” with severe heat stress persisting even when adjacent vegetated plots were cooler (Shashua-Bar et al., 2011). Given that we walked with sensors beside a busy road and a light-rail track, long-wave radiation from these pavements may have raised the local heat index enough to mask the differences measured among park strip cover types.
Another factor could be the surface reflectance of each material. In the same study mentioned above, grass surfaces stayed cooler because of irrigation rather than albedo. Conversely, bright paving such as concrete reflected more short-wave energy back to pedestrians, increasing heat index in the area (Shashua-Bar et al., 2011). Along W North Temple, park strip covers like gravel and areas with an extended sidewalk rather than a dedicated park strip cover may have reflected more sunlight towards pedestrians, further reducing the impact park strip covers had on air temperature and, consequently, pedestrian heat index.
Cooling from vegetation also depends heavily on water supply. A review of urban evapotranspiration studies reported that properly watered green areas, like grass, can lower surrounding air temperature by 0.5 to 4 °C (Qiu et al., 2013). Because our route consisted of dry park strip covers during the 4:00 to 6:00 PM MST window we walked, an uncommon sprinkler watering times, the grass strips we recorded may have been too dry to provide this benefit to pedestrian walkers.
Finally, anthropogenic heat released by traffic may have added a steady increase in heat along the whole route. Reviews of urban heat island drivers frequently list vehicle exhaust and other human sources as a primary contributor to elevated city temperatures (Qiu et al., 2013). Because our walk was conducted during a peak communing time for workers within the city, these cars likely heated the surrounding environment enough to further dilute the microclimatic cooling from park strip covers and canopy coverage along our route.
Our findings, combined with these potential external factors, imply that isolated design interventions, such as changing park strip cover, may be insufficient in hot urban corridors. In other words, alleviating pedestrian heat stress may require additional interventions that help reduce those larger impacts, such as more consistent canopy placement and engineered shade, reflective surfaces to reduce asphalt emanation of heat, irrigation schedules altered to align with peak foot traffic, and strategies to reduce car emissions in the area through improved public transportation. Additionally, future studies could consider using fixed surface and radiant sensors to measure differences in park strip cover heat index more precisely. This would help capture a better understanding of the influences of park strip cover by isolating their effects more closely compared to the mobile sensor monitoring performed in this study.
Bibliography
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