Pedestrians

Objective neighborhood walkability indicators were created via geographic information systems (GIS) using ArcGIS 9.3. GIS data were analyzed using the North American Datum (NAD) 1983 state plane coordinate system for each of the four metropolitan areas. This study includes total retail walking destinations (e.g., clothing stores, pharmacy/drug stores, bookstores) per square kilometer, total service walking destinations (e.g., post offices, banks, credit unions) per square kilometer, total cultural/educational walking destinations (e.g., movie theaters, schools, libraries) per square kilometer, parks per square kilometer, median pedestrian route directness (median of the ratio of distance between one point and another via the street network and straight-line distance between the two points; values closer to 1.00 represent a more direct route or a more connected network), intersection density (the number of street intersections per square kilometer; intersections are defined as street network nodes with three or more associated street segments excluding highways), count of cul de sacs (based on nodes associated with only one street segment), average speed limit (miles per hour), highway density (percentage of area that is highway traveled right of way; class 1 and 2 highways were used), residential density (US census block group occupied housing units per square kilometer were weighted proportionally for the child’s defined neighborhood) and population density (US census block group total population per square kilometer were weighted proportionally for the child’s defined neighborhood). We limited the retail, service and cultural/educational walking destinations to locations with fewer than 250 employees to filter out large businesses (e.g., Costco, Home Depot) as business with greater than 250 employees can take away from the walkability of a neighborhood (e.g., by having large parking lots) [22 ]. Retail, service and cultural/educational walking destinations data come from ESRI Business Analysis InfoUSA Business Locations 2006. ESRI Data and Maps information, from ESRI, has spatial datasets representing several built environment features. InfoUSA (http://infousa.com) is a company that provides listings of private and public businesses (verified yearly by telephone), with 6-digit NAICS codes as well as numbers of employees. Locations of these businesses had been geocoded and were available as a spatial dataset through the ESRI Business Analyst Extension. Data on parks, intersection density, cul de sacs, average speed limit, and highway density come from ESRI Data and Maps 2006; median pedestrian route directness data are derived from ESRI Business Analyst Info USA Business Locations 2006. Residential density and population density data as previously described come from 2000 US Census. This geospatial dataset includes GIS-derived walkability indicators for neighborhoods defined as 400-, 800- and 1600-meter street network buffers. We specifically selected 400- and 800-meters for our small spatial scales because these distances are considered a proximal neighborhood environment for children and adolescents [23 (link),24 (link)], among other populations such as older adults [25 (link)–28 (link)]. The 1600-meter buffer was used because it is approximately 1-mile, which is consistent with the Walk Score algorithm. The street network buffers were created from StreetMap streets excluding highways and ramps using the ArcGIS Network Analyst Extension. The street network buffers consisted of 50-meter buffers around street center lines that extend along the network 400-, 800- and 1600-meters from the geocoded home addresses.

The study was a concurrent cohort study, including all the BAT patients who presented to the emergency room of El Demerdash Hospital. It is a quaternary hospital, which is the surgical hospital of Ain Shams University Hospitals, Cairo, Egypt. On average, it has more than 7,000 annual emergency room visits for diagnoses related to trauma [21 ]. It has around 15,500 emergency admissions yearly, more than 2,500 of them are trauma patients, and about 800 patients are discharged within 24 hours after being stabilized and investigated. The study period was between November 2018 and October 2019. Included patients were those who presented within 24 hours after the trauma and with a Glasgow Coma Scale score greater than 8 to ensure a reliable examination, and were assessed by FAST. Exclusion criteria were as follows: BAT patients discharged without a CT scan, patients with a prehospital urinary catheterization, patients with a known history of bleeding disorders, patients with liver cirrhosis or a known history of ascites, and those with urinary diversion.
All patients underwent the usual pathway of trauma patients adopted by the hospital, which included history taking, examination (primary and secondary surveys), trauma laboratory studies, and radiologic studies, which included a FAST and an abdominopelvic CT scan. The FAST was performed for all patients by a well-trained radiology specialist registrar. The presence of hematuria was tested in the urine samples using a dipstick test (Medi-Test Combi 11, MACHEREY-NAGEL GmbH & Co. KG, Düren, Germany).
Patients were subdivided into two groups according to the findings of the CT scan. The workflow of the patients is shown in Figure 1.
Ethical approvals
The study was approved by both the Research Ethics Committee (REC), General Surgery Department, Ain Shams University (IRB: 00006379), and the University of Maryland, Baltimore (UMB) Institutional Review Board (IRB), and it followed the tenets of the Declaration of Helsinki.
Operational definitions
“Road traffic crashes (RTC)” are all accidents related to moving vehicles, the patient may be the drivers, vehicle passengers, or pedestrians. “Falling from a height” is falling from one or more story heights, i.e., more than three meters. “Falling” is falling from less than one story height, like slips, stumbles, or falling down stairs.
Statistical analysis
The collected data were coded, tabulated, and statistically analyzed using IBM SPSS Statistics software version 22.0 (IBM Corp., Armonk, NY).
The descriptive statistics were done for the quantitative data as mean ± SD, and as number and percentage for the qualitative data. The inferential analyses were done for the quantitative variables using the independent t-test; while for the qualitative data, the inferential analyses for the independent variables were done using the chi-square test for differences between proportions and the Fisher’s exact test for the variables with small expected numbers. A p-value less than 0.05 was considered to be statistically significant, otherwise, it is non-significant.
Availability of data and materials
The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

If a collision impulse $\mathrm{\Delta }{\stackrel{\rightharpoonup }{\mathit{L}}}_0$ made individual i lose their balance and there was an individual k around individual i, then the secondary collision could occur for the case where individuals collided with each other in an unstable posture. Depending on the empirical formula obtained in the experiments ^{39 (link)}, the secondary collision impulse could be approximately solved as: $$\mathrm{\Delta }{\overrightarrow{L}}_{\mathit{jk}}=\left[a{exp}^{p{m}_j{d}_{\mathit{jk}}/(\mathrm{\Delta }{\overrightarrow{L}}_0·{\overrightarrow{n}}_{\mathit{jk}})}+b{exp}^{q{m}_j{d}_{\mathit{jk}}/(\mathrm{\Delta }{\overrightarrow{L}}_0·{\overrightarrow{n}}_{\mathit{jk}})}+\delta \right]·\left(\mathrm{\Delta }{\overrightarrow{L}}_0·{\overrightarrow{n}}_{\mathit{jk}}\right)·{\overrightarrow{n}}_{\mathit{jk}}$$ where m_j represents the mass of the human body j, d_jk represents the distance between the mass center of individuals j and k, ${\overrightarrow{\mathbf{n}}}_{\mathit{jk}}$ represents the normal direction vector from individual j to k, and the constant $a=0.32$ , $b=1.33$ , $p=1.21$ , $q=-4.99$ . According to the experiments^{43 (link)}, there were slight differences in $\mathrm{\Delta }{\mathit{L}}_{\mathit{jk}}/\mathrm{\Delta }{\mathit{L}}_0$ at different positions in the queue. Therefore, in this paper, $\delta$ was set to obey the normal distribution N(− 0.2, 0.05) if there were no pedestrians restricting the movement of the collided individual within the available range, and $\delta$ obeyed the normal distribution N(− 0.2, 0.05) in other cases.