Urban areas around the world have been constantly growing since the beginning of the 19th century. And by 2050, 68% of the world’s population is expected to be urban (Nations, 2019). Increasing urbanization leads to many challenges in terms of traffic congestion and cities’ infrastructure to keep up with the populational growth and at the same time improve the living standards of the population in social, economic and environmental terms.
The effects of large-scale urbanization are especially visible in the transportation sector. Cities’ public transit networks are often overcrowded and so, populations recur to private cars raising CO2 emissions and stress levels, undermining life quality (Schrank et al., 2019). The promotion of ‘active travels’, which encompasses walking and the use of micro-vehicles such as bikes, e-bikes and e-scooters, is a promising way to reduce Greenhouse gas (GHG) emissions (Brand et al., 2021) as well as to greatly reduce congestion in busy corridors of big metropolitan areas (Fan & Harper, 2022; Hamilton & Wichman, 2018).
E-micromobility (EMM) is a practical solution for short-distance commuters, and it is growing at upsetting rates. Electric mobility and micromobility transformed the panorama in larger metropolises, given their accessibility, large availability, and the potential to be not only a time saver in short trips but also to be a sustainable alternative in some scenarios. Given the fact that 35% of all the private car trips in the U.S. are under 3.2 km (NACTO, 2019), shifting from a car to a micro-vehicle does not only have benefits in terms of reducing congestion, but it can also decrease the emissions of an average person by 3.2 kg CO2 per day (Brand et al., 2021). Moreover, it has been shown that the integration of public transportation and e-scooters can be a viable alternative to replace private cars as long as there is a good infrastructure in place (Oeschger et al., 2020). However, it has led to an increase in accidents involving e-scooters, with many of the injured ending up at the hospital’s emergency departments (Austin Public Health, 2019; Badeau et al., 2019; Bloom et al., 2020). More worrying is that traumatic brain injury (TBI) accounts for a considerable portion of e-scooter related injuries, reaching up to 40.2% of the cases as shown by a study conducted at two hospitals in southern California (Trivedi et al., 2019). Amongst bike riders, the head is the most frequently severely injured part of the body (Deck et al., 2019; Rizzi et al., 2013). Many studies have proven that wearing a helmet is extremely important in reducing the odds of having a serious head injury, with conclusions estimating a reduction of severe injuries to the head and brain from 63–88% (Thompson et al., 1999) and, for TBI alone, about 53% (Høye, 2018). Biomechanical studies have been stating the enormous difference a helmet makes in preventing head injuries during head impact (Cripton et al., 2014; Fahlstedt et al., 2016; McIntosh et al., 2013; McNally & Whitehead, 2013). For example, Cripton et al (Cripton et al., 2014) by pairing helmeted and unhelmet impacts verified that the helmets decreased the head peak acceleration from 824 to 181 g, therefore reducing the risk of skull fracture from near certainty to only 5%.
Nevertheless, despite the evident importance of helmet use, there are concerning numbers regarding the very low use of helmets in the cities. Amongst bike riders, according to several observational studies (Basch et al., 2015; Bonyun et al., 2012; Goodman et al., 2014; Grenier et al., 2013; Kraemer et al., 2012), the number of helmeted individuals is no higher than 25.4%, with the lowest being 11.1% in New York (Basch et al., 2015). Regarding e-scooter sharing systems helmet use averages a staggering 8.8% according to a review conducted by Serra et al (Serra et al., 2021). And since the number of users wearing a helmet is inversely proportional to the ever increasing one of users and injuries, this is a new public health problem (Rivara, 2019). Moreover, traditional helmets for bikers seem not to be adequate to this new mobility trend, where spontaneity is the main characteristic (Serra et al., 2021).
Another inadequacy of current helmets is in terms of ergonomics. Women are generally under-represented in research data and findings, which is translated into real word designs, like the bicycle helmets, which usually take a unisex approach to their sizing. Male and female head anthropometric measurements are significantly different, being normally smaller in the latter (Vasavada et al., 2008). Ignoring such differences can, besides affecting comfort, ultimately lead to safety hazards, as reported by Criado Perez (Criado Perez, 2020).
Another issue is related to sustainability. The use of mostly petrol-derived materials such as Polycarbonate (PC), acrylonitrile butadiene styrene (ABS), expanded polystyrene (EPS), amongst others, in combination with the regular manufacturing method for these protection devices, the in-mould injection, which bonds the foam and the hard shell together through heat and pressure, can impair the recycling of the entire helmet. Foams such as the EPS, the most used for the helmet’s liner, cannot offer the same level of protection after the first impact because it deforms permanently, substantially decreasing its energy absorption capability (Fernandes et al., 2015), therefore, giving no other choice but to be discarded and replaced by a new one. Therefore, a material that would be capable of resisting multiple impacts would greatly improve the helmet’s environmental performance, by slowing resource loops, i.e., extending the product’s life, and potentially enabling its integration into a circular economy, as well as its overall impact performance.
The aim of the current paper is to showcase the development of an eco-friendly solution for a helmet designed for urban micromobility considering all aspects of sustainability from early stages of the design process as well as the necessary experimental campaign to find the best combinations of materials to be used in order to ensure the feasibility and, most importantly, the safety of the proposed solution.